Screening flame retardants using milligram-scale flame calorimetry Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-24 Fernando Raffan-Montoya, Stanislav I. Stoliarov, Sergei Levchik, Eyal Eden
A variety of flame retardants and synergistic additives have been developed over the years in order to address the inherent flammability of polymeric materials. Environmental and economic concerns have recently driven industry to replace some of these flame retardants and synergists. Screening for potential replacements can be costly due to a variety of reasons. While some methods have been developed to screen flame retardants in a cost-effective manner, there is currently a need for a method that can also produce high quality data that provide insight into the physics behind the observed behavior during screening. This work proposes the use of Milligram-scale Flame Calorimetry (MFC) as a method to screen flame retardants in a highly quantitative, cost-effective manner. A methodology based on MFC measurements is presented and subsequently implemented using poly (butylene terephthalate) (PBT) as the base polymer and poly (pentabromobenzyl acrylate) (FR-1025) as the base flame retardant. This combination was chosen due to its well-understood behavior and compatibility. Using this polymer and flame retardant as a base, the flame retardant activity of antimony trioxide (ATO), aluminum hypophosphite (AL-HYPO) and a combination of melamine polyphosphate (MPP) and a proprietary formula (SOL-DP) as additives was explored with the proposed methodology. The fact that these measurements were performed with dry-blending of relatively small amounts per composition, as well as the milligram-scale nature of the measurements should represent a significant reduction in testing times and cost with respect to other available screening methods. The results show the outstanding performance of ATO, as measured by reduction in the heat of combustion. ATO performance is shown to be highly synergistic. For AL-HYPO, and MPP + SOL-DP, the performance is lower with respect to ATO. AL-HYPO does not exhibit synergistic behavior, although certain loadings can lead to lower heats of combustion. The complex interactions between FR-1025, MPP and SOL-DP show that some binary interactions are antagonistic while others are synergistic. Insight into the mode of action (gas-phase versus condensed-phase) was also revealed by the methodology with ATO exhibiting gas-phase-dominated activity, Al-HYPO showing a mixture of gas-phase and condensed-phase activity with no single mode standing out, while MPP + SOL-DP being predominantly condensed-phase active. Given a desired performance (for example, a range of desired heat of combustion values), the methodology allows for identification of optimum formulations that lead to said performance.
High performance polyurethane dispersion synthesized from plant oil renewable resources: A challenge in the green materials Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-23 T. Gurunathan, Ravi Arukula
Effect of stoichiometry on the thermal stability and flame retardation of polyisocyanurate foams modified with epoxy resin Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-22 Keping Chen, Chunrong Tian, Shuen Liang, Xiuli Zhao, Xiaolin Wang
Epoxy resin modified polyisocyanurate (EP-PIR) foams were successfully prepared by the reaction of polymethylene polyphenylene isocyanate (PAPI) and diglycidyl ether of bisphenol-A (DGEBA). Thermogravimetric analysis coupled with infrared spectrometry (TGA-IR) was performed to investigate the thermostability and the gaseous pyrolysis products of EP-PIR foams. The results indicated that the excellent thermostability of EP-PIR foams was due to the abundant highly thermostable isocyanurate ring and oxazolidone ring. The flame retardation of EP-PIR foams was also investigated. UL94 results revealed that the foams with [PAPI]/[DGEBA] ratio above 2.5 could reach V-0 classification. With increasing the stoichiometry of [PAPI]/[DGEBA], the limiting oxygen index values increased linearly from 24.5 to 30.0 vol %. Scanning electron microscopy images of burned foams illustrated the flame-retardant mechanism was due to the excellent charring ability. Cone calorimeter tests showed that the peaks of heat release rate were always as low as 266.5 kW/m2. Moreover, highly thermostable isocyanurate ring played an important role in the suppression of smoke emission.
Influence of atmospheric pressure dielectric barrier discharge on wettability and drying of poly(ether-ether-ketone) foils Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-22 Radka Štefaníková, Tereza Kretková, Anna Kuzminova, Jan Hanuš, Mykhailo Vaidulych, Ondřej Kylián, Hynek Biederman
Wettability and water droplet drying dynamics on poly(ether-ether-ketone) (PEEK) foils treated by atmospheric pressure air dielectric barrier discharge (DBD) has been investigated. It has been found that plasma treatment causes significant increase of PEEK wettability that is predominantly connected with alterations of its chemical composition (oxidation) induced by DBD plasma. The hydrophilization of PEEK surface was not temporally stable and substantial increase of water contact angle up to 67° was observed with increasing storage time, which is consistent with loosening of polar groups as confirmed by means of XPS. Characteristic restoration time of the contact angle was 6.7 days. Furthermore, a large alteration of the dynamics of water droplets drying on PEEK after the plasma treatment was also observed: whereas for untreated PEEK three drying phases were clearly distinguishable, the phase of constant contact angle disappeared in the case of PEEK exposed to the atmospheric pressure air plasma. In spite of substantial decrease of PEEK wettability with storage time the constant angle phase didn't appear within 51 days after the plasma treatment. As a result of this plasma treated and aged PEEK exhibits much higher water contact hysteresis as compared to untreated PEEK. This effect may be explained by the formation of randomly distributed nanostructures on PEEK surface exposed to DBD plasma that increase the spatial heterogeneity of the PEEK surface and enhances droplet pinning during its drying.
Study on the oxidative stabilization of polyacrylonitrile fibers by microwave heating Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-21 Jianhua Liu, Shijie Xiao, Zhigang Shen, Lei Xu, Libo Zhang, Jinhui Peng
A microwave heating method was used for oxidative stabilization of polyacrylonitrile (PAN) fibers. The bulk density, chemical structure (FTIR), crystalline structure (WAXD), and skin-core structure were studied. The results show that the intermolecular cyclization happened above 220 °C. From X-ray diffractograms of heat treated fibers, the pre-graphitic structure of stabilized fibers was developed to turbostratic structure. A gradual densification of the fibers occurring was observed after stabilization at a maximum temperature of 240 °C. Microwave heating effectively shortened the thermal stabilization process and the thermal stabilization time by 35 min compared with the conventional thermal stabilization process. The skin-core structure of the stabilized fibers was prohibited by microwave heating.
Miscibility and degradation of polymer blends based on biodegradable poly(butylene adipate-co-terephthalate) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-21 Ainara Sangroniz, Alba Gonzalez, Loli Martin, Lourdes Irusta, Marian Iriarte, Agustin Etxeberria
Thermal properties and thermal stabilization of lignosulfonate-acrylonitrile-itaconic acid terpolymer for preparation of carbon fiber Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-19 Dapeng Liu, Qin Ouyang, Xuefeng Jiang, Hongbo Ma, Yousi Chen, Liu He
Lignin, the most abundant aromatic biopolymer on the earth, is considered as a sustainable carbon fiber precursor. However, lignin-based carbon fibers face great challenges in the fiber spinning and thermal stabilization due to the complex structure of lignin. In this work, lignosulfonate-acrylonitrile-itaconic acid (LS-AN-IA) terpolymer with excellent spinnability was prepared as a novel precursor for carbon fibers, and the thermal properties and thermal stabilization of this precursor were studied. The introduced itaconic acid (IA) comonomer was found to play an important role in improving the thermal properties and promoting the thermal stabilization. The hindering effect of LS on the cyclization reaction of nitrile groups was overcome by the IA comonomer through changing free-radical reaction mechanism to an ionic one. The thermal stabilization of the LS-AN-IA terpolymer precursor fibers could be carried out at a lower temperature and required a shorter time, which helped to reduce the energy and time consumption. Carbon fibers with tensile strength and tensile modulus of 1.74 GPa and 210 GPa, respectively, were obtained from the LS-AN-IA terpolymer.
Microscopic structural changes during photodegradation of low-density polyethylene detected by Raman spectroscopy Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-19 Yusuke Hiejima, Takumitsu Kida, Kento Takeda, Toshio Igarashi, Koh-hei Nitta
The effect of crystalline phase (anatase, brookite and rutile) and size on the photocatalytic activity of calcined polymorphic titanium dioxide (TiO2) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-17 Norman S. Allen, Noredine Mahdjoub, Vladimir Vishnyakov, Peter J. Kelly, Roelof J. Kriek
The effect of thermal treatment on the morphology (crystalline phase and size) and photocatalytic activity of freshly prepared TiO2 nano-powder is communicated. TiO2 nano-powders, prepared by hydrolyzing titanium tetraisopropoxide at room temperature, were all dried at 382 K and subsequently calcined at different temperatures, for 1 h, up to 1172 K. Raman analysis of each thermally treated sample exhibited different titania phase structures. Up to 772 K a mixture of brookite and anatase phases was observed, while a mixture of all three phases, i.e. anatase, brookite and rutile, was observed at 872 K, with a rutile only phase at 1097 K and above. The photocatalytic activity of all samples was assessed by means of the photocatalytic degradation of methyl orange dye (MeO). All anatase-brookite compositions exhibited high photocatalytic activity with the rate of degradation decreasing with increasing calcination temperature, which coincides with (i) a slight increase of the anatase phase, (ii) a slight decrease of the brookite phase, and (iii) a gradual increase of the crystallite size of all phases. The greatest photocatalytic activity was observed for the sample calcined at 382 K, which contained the highest amount of brookite (in the presence of anatase as the dominant phase), while the lowest rate was observed for the pure rutile sample.
Thermal, thermo-oxidative and thermomechanical degradation of PLA: A comparative study based on rheological, chemical and thermal properties Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-16 A.A. Cuadri, J.E. Martín-Alfonso
This research studies the effect of thermal, thermo-oxidative and thermomechanical degradation conditions on the melt rheological, chemical and thermal properties of PLA at temperatures around its normal processing temperature. Thermal and thermo-oxidative degradations were conducted on a rheometer by using nitrogen or air as gas, respectively, and the thermomechanical degradation was performed on a mixer equipped with two counter-rotating rollers. Dynamic oscillatory rheology, TGA, DSC and FTIR were performed on PLA samples subjected to different degradation conditions: temperature (180, 200 or 220 °C), time (15, 30 or 60 min), atmosphere (air or atmosphere) and the application of mechanical stress or not. Thus, rheological results indicate the synergic effect that temperature, mechanical stress and time exerts on the extent of chain scission phenomena, which was also corroborated by FTIR results; however, the individual contribution of mechanical stress diminishes gradually with the degradation time, being more pronounced for higher degradation temperature. In addition, degree of crystallinity (χc) turned out not to be a suitable parameter for comparing degraded samples, since all of them became amorphous after degradation. Instead, glass transition (Tg) and cold crystallization (Tcc) temperatures as well as the cold crystallization enthalpy (ΔHcc) reveal that the chain scission phenomena makes degraded samples easier to crystallize. Finally, TGA results point out a worsening of the PLA thermal stability, with lower values of the characteristic temperatures (T5% and Tmax) for degraded samples.
Effect of sodium hypochlorite exposure on polysulfone recycled UF membranes and their surface characterization Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-16 Serena Molina, Junkal Landaburu-Aguirre, Laura Rodríguez-Sáez, Raquel García-Pacheco, José G. de la Campa, Eloy García-Calvo
The present work aims to investigate the effect of chlorine on the surface of the polysulfone (PSF) layer uncovered in the transformed ultrafiltration (UF) membranes (recycled from end-of-life reverse osmosis (RO) membranes). With this purpose, 6 end-of-life RO membranes used previously during their useful life to treat brackish water or seawater were transformed using two higher exposure doses of free chlorine (50,000 and 300,000 ppm h). On one hand, the end-of-life membranes were first characterized in terms of the type of fouling identified by TGA, ICP and bacteria detection. On the other hand, to determine the stability of the PSF layer, the transformed PSF UF membranes were then characterized by means of its permeability and molecular weight cut-off (MWCO). In addition, membrane surface characterization was performed by ATR-FTIR, SEM and AFM. The results show that all the end-of-life RO membranes with organic and inorganic fouling were effectively transformed to PSF UF membranes at the ppm∙h values studied. However, one of the analysed sea water membrane model (HSWC3) showed more resistance to be transformed and the pores of the uncovered PSF layer only appeared at 300,000 ppm h. This membrane showed different surface appearance, with bigger pores after 300,000 ppm h exposure dose that might have affected the PSF UF membrane performance. This study indicates that a complete characterization of transformed PSF UF membrane surface is crucial for a deep understanding of the recycling process of end-of-life membranes.
Hydrolytic degradation kinetics of bisphenol E cyanate ester resin and composite Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-16 James A. Throckmorton, Greg Feldman, Giuseppe R. Palmese, Andrew J. Guenthner, Kevin R. Lamison, Neil D. Redeker, Patrick N. Ruth
Preparation of a novel polysiloxane and its synergistic effect with ammonium polyphosphate on the flame retardancy of polypropylene Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-14 Zhilei Zhao, Qing Jin, Naien Zhang, Xiaorong Guo, Hong Yan
A novel polysiloxane (APID) containing phosphorus, nitrogen and benzene rings was synthesized as a flame retardant, which is hydrophobic and thermally stable in air (residual weight being 46.1 wt.% at 800 °C). APID is synergistic with ammonium polyphosphate (APP) in the formation of strong cross-linked intumescent char layer, resulting in improved flame retardancy, smoke suppression and dripping resistance of polypropylene (PP). With 23 wt.% of APP and APID (3:2), the flame retarded PP achieved V-0 rating at UL-94 test and its peak heat release rate was reduced by 75.7% in the cone calorimeter test. Moreover, APID improved the compatibility of APP with PP matrix to minimize the negative effect of APP on the mechanical properties of PP. The detailed flame retardant mechanism was discussed in the text.
Ceramifiable EVA/APP/SGF composites for improved ceramifiable properties Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-13 Dong Zhao, Yucai Shen, Tingwei Wang
Ceramifiable ethylene-vinyl acetate (EVA) copolymer composites were prepared through incorporating silicate glass frits (SGF) and ammonium polyphosphate (APP) into the EVA. The ceramic residues were obtained by firing all samples at different temperatures. The effect of APP on the self-supporting property and shape stability of the composites were studied, and the effect of APP on the flexural strength and water absorption of the ceramic residues were investigated. The results show that the addition of APP improved the self-supporting property and the flexural strength of the composites due to the increased crystal phase. The shape stability and the porous structure of the residues increased due to water and NH3 released from the thermal decomposition of APP. XRD and SEM analysis demonstrated that APP promotes the precipitation of sodium phosphate and cristobalite. Furthermore, the growth process of the crystal was investigated by crystallization kinetic.
Polycaprolactone-collagen hydrolysate thermoplastic blends: Processability and biodegradability/compostability Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-10 Maurizia Seggiani, Roberto Altieri, Monica Puccini, Eleonora Stefanelli, Alessandro Esposito, Francesco Castellani, Vitale Stanzione, Sandra Vitolo
Thermoplastic blends of polycaprolactone (PCL) and hydrolyzed collagen (HC) derived from the tannery industry were investigated to assess the feasibility of producing by conventional melting-based procedures biodegradable items for applications in agriculture and plant nurseries. The used HC was obtained by alkaline hydrolysis of the shavings of the tanning process. PCL/HC blends, with 10, 20 and 30 wt.% of HC, were processed by extrusion and compression molding, and characterized in terms of thermal, rheological, morphological and mechanical properties. In view of their possible applications in agriculture, phytotoxicity assays were carried out by using cress (Lepidium sativum L.) germination test and growth analyses of lettuce plants (Lactuca sativa L., cv Canasta), used as reference. Small pots were produced by fusion deposition modeling (FDM) and their compostability was evaluated by the standard disintegration test UNI EN ISO 14045. The ultimate aerobic biodegradability of the blends was assessed by the standard UNI EN ISO 14855-1. PCL/HC blends were successfully processed by extrusion providing cohesive and flexible filaments suitable for the FMD 3D-printing. A decrease in the melt viscosity was observed with the addition of HC due to its plasticizing effect. The addition of HC led to a clear decrease of the tensile modulus and, with 30 wt.% HC, a break elongation higher than 600% as pure PCL. Despite the release in water of soluble salts, responsible of a moderate phytotoxicity assessed by L. sativum germination test, PCL/HC blends were not phytotoxic to the lettuce growth. Moreover, PCL/HC blends showed very high biodegradation rates in compost, even higher than cellulose. Composting trial performed under real conditions also confirmed the biodegradability of these blends, showing complete disintegration of the produced 3D printed pots in just 30 days.
Filler and additive effects on partial discharge degradation of PET films used in PV devices Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-09 Rong Tang, John J. Liggat, Wah H. Siew
A series of poly(ethylene terephthalate) (PET) films with different additives were subjected to identical electrical stresses to investigate their partial discharge (PD) degradation behaviour. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to study the surface chemistry changes of the degraded samples. The filled samples showed markedly better PD resistance and lifetime compared to the unfilled PET. A filler ‘pile-up’ effect has been directly observed for the filled samples and is proposed as the mechanism underlying the enhanced stability. PD-induced breakdown results also revealed that TiO2 filled PET has a superior PD lifetime to BaSO4 filled PET, which could be attributed to both the higher permittivity of the TiO2 fillers and the voids that are created around the BaSO4 particles during the film orientation process. Further improvements to PD resistance and PD lifetime, through the reduction of surface oxidation, are observed for a BaSO4-filled sample additionally containing the UV stabilizer Tinuvin 1577.
Comparison of PCL degradation in different aquatic environments: Effects of bacteria and inorganic salts Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-09 Bo Lu, Ge-Xia Wang, Dan Huang, Zhong-Lai Ren, Xiao-Wei Wang, Ping-Li Wang, Zhi-Chao Zhen, Wei Zhang, Jun-Hui Ji
Six different water bodies of different salinities and bacteria were set up to study the effects of microorganisms and salts on the degradation process of biodegradable polycaprolactone (PCL) spline. The experimental data for a 52-week period consistently indicate that both microorganisms and salts have an impact on the degradation process. PCL shows slow bulk hydrolysis in aseptic water and relatively rapid interfacial enzymatic degradation in bacteria-containing water however. The degradation rate of PCL in lab-prepared high-salinity seawater was noticeably higher than that in distilled water and low-salinity seawater, indicating a salt-driven acceleration of PCL hydrolysis. Because of the combined effects of factors such as the presence of bacteria, salinity, and external forces in the sea, PCL degrades fastest in natural seawater, losing 29.8% of its original weight in 52 weeks.
Effects of γ-ray treatment on paper Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-08 Floriana Coppola, Flavia Fiorillo, Alberto Modelli, Matteo Montanari, Mariangela Vandini
The effects of γ-irradiation and thermal drying treatments at an industrial level, and accelerated ageing on the properties of pure cellulose paper are investigated with a multi-disciplinary approach. Viscometry is used for measuring the degree of polymerisation, visible reflectance spectroscopy for colour changes, tensile strength and tearing resistance tests for mechanical properties, Fourier transform IR spectroscopy and scanning electron microscopy for possible chemical or physical modifications of the surface. The results indicate that γ-rays (5 and 10 kGy) cause a sizeable reduction of the degree of polymerisation, but only small colour changes, while larger effects on the colour are caused by the synergetic effect of ageing. In spite of the large degree of polymerisation decrease, γ-irradiation is found to only slightly affect the mechanical properties, as well as thermal and ageing treatments. No clear evidence for changes in the FTIR spectral features due to the treatments employed is found.
Peculiar effect of stereocomplexes on the photochemical ageing of PLA/PMMA blends Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-08 Géraldine Rapp, Cédric Samuel, Jérémy Odent, Jean-Marie Raquez, Philippe Dubois, Pierre-Olivier Bussière, Jean-Luc Gardette, Sandrine Therias
Degradation behavior and kinetics of sisal fiber in pore solutions of sustainable cementitious composite containing metakaolin Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-05 Jianqiang Wei
Thermal decomposition studies on polyurethane elastomers reinforced with polyhedral silsesquioxanes by evolved gas analysis Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-05 Joanna Pagacz, Edyta Hebda, Bartłomiej Janowski, Dariusz Sternik, Małgorzata Jancia, Krzysztof Pielichowski
In this work, we report on the thermal stability of nanohybrid polyurethane (PU)/polyhedral oligomeric silsesquioxanes (POSS) elastomers analyzed by evolved gas analysis (EGA). Functionalized POSS were chemically introduced into PU structure as pendant groups (1,2-propanediolizobutyl POSS (PDI-POSS), disilanollsobutyl POSS (DSI-POSS)) or as chemical crosslinks (octa(3-hydroxy-3-methylbutyldimethylsiloxy) POSS (OCTA-POSS)). EGA results of the thermal degradation of the PU/POSS hybrid elastomers have demonstrated that the hybrid systems are slightly more thermally stable when compared to the unmodified PU matrix, as evidenced by reduced amounts of volatile degradation products. It was found that the thermal decomposition of polyurethane materials reinforced with POSS starts from about 300 °C via urethane bonds breakage. In lower temperature region the modified polyurethanes decompose to some low molecular weight compounds and intermediates with hydroxyl and amine groups. At temperatures above 350 °C evolution of hydrocarbons, aldehydes, alcohols, amines, cyclic species and low molecular weight compounds - carbon monoxide, carbon dioxide, water and ammonia was recorded. Furthermore, the inclusion of POSS in the PU network directly influences the degradation pathways of both the soft and hard block components of the elastomers – it has been observed that the POSS/PU hybrid systems show reduced levels of CO2 and changed levels of characteristic ion fragments, e.g. m/z 42 related to hydrocarbons and THF.
Bis-uracil based high efficient heat stabilizers used in super transparent soft poly (vinyl chloride) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-02 Bozhen Wu, Yating Wang, Si Chen, Muyan Wang, Meng Ma, Yanqin Shi, Xu Wang
Two novel kinds of bis-uracil derivative based organic stabilizer with different length of alkyl chains to provide outstanding compatibility with poly (vinyl chloride) (PVC) were designed and synthesized in this paper, which exhibited high efficient thermal stability and could get super transparency PVC composites. After confirming the structures of 6,6′-diamino-1,1′,3,3′- tetramethyl-5,5´-(octylidene)bis[pyrimidine-2,4(1H,3H)-dione] (OSU) and 6,6′-diamino-1,1′,3,3′-tetramethyl -5,5´-(hendecylidene)bis[pyrimidine-2,4(1H,3H)-dione] (USU) by Fourier infrared spectrum (FT-IR) and Mass spectra, 2 phr of each was introduced into PVC respectively to verify that bis-uracil derivatives could absorb HCl released by PVC to enhance the thermal stability, confirmed through discoloration and Congo red tests, but the initial whiteness was not satisfied. In addition, epoxy soybean oil (ESBO) and phosphite ester showed excellent synergistic effects with OSU and USU that could effectively further improve the initial whiteness, thermal stability and transparency of PVC samples, proved by discoloration tests, UV vis spectrophotometer and transmittance/haze tests. We believe that such complex stabilizers without any metallic elements may widen the applications of the resultant soft transparent PVC in artificial leather, wire and cable, packing materials and so on.
Polyethylene loss of ductility during oxidation: Effect of initial molar mass distribution Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-31 Armando F. Reano, Alain Guinault, Emmanuel Richaud, Bruno Fayolle
This paper reports a study of thermal oxidation induced embrittlement in several polyethylene grades differing mainly by the broadness of the molar mass distribution (ranging for lower than 3 to more than 30). Thermal oxidation was monitored at macromolecular scale (Gel Permeation Chromatography, Differential Scanning Calorimetry) and macroscopic scale (tensile tests). As expected, the samples undergo predominant chain scission and plastic deformation is suppressed below a critical molar mass value (M’C). Even though this latter was previously reported to be independent of the initial weight average molar mass, it is shown here that it depends on initial polydispersity index. Samples were also shown to undergo chemicrystallization, i.e. that segments released by chain scissions migrate into the crystalline phase with a yield increasing with initial polydispersity index. Finally, the main novelty of this work is to evidence that the previously proposed end-of-life criteria at macromolecular level linked to loss of ductility (critical molar mass, crystallization yield) depend on the initial polydispersity index.
Flame-retarding epoxy resin with an efficient P/N/S-containing flame retardant: Preparation, thermal stability, and flame retardance Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-31 Pan Wang, Long Xia, Rongkun Jian, Yuanfang Ai, Xuelin Zheng, Guilin Chen, Junsheng Wang
To further study the effect of the phosphorus, sulfur, and nitrogen-containing flame retardant on epoxy resin, a DOPO-based phenol derivative 4-[(benzothiazolyl 2-amino)(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl) methyl] phenol namely D-P-A, was successfully synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), p-hydroxybenzaldehyde (PHBA), and 2-aminobenzothiazole (ABZ), and used to flame retard epoxy resin (EP). As expected, D-P-A imparted flame retardance to epoxy resin. For example, with 7.5 wt% loading of D-P-A, epoxy thermoset passed a UL-94 V-0 rating, and got a LOI value of 29.6%. Besides, D-P-A played an effective role in inhibiting heat release of EP, that EP/7.5% D-P-A showed a peak of heat release rate (PHRR) of 713 kW/m2 much lower than 1137 kW/m2 of EP. However, it decomposed in advance owing to the lower thermal stability of D-P-A. Finally, through Scanning electron microscopy (SEM), Raman spectra and X-ray photoelectron spectroscopy (XPS) and pyrolysis-gas chromatograph/mass spectrometer (Py-GC/MS), it disclosed that D-P-A exerted its flame-retardant activity both in the vapor and condensed phase.
Femtosecond laser-induced modification of PLLA/hydroxypatite composite Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-31 K. Szustakiewicz, B. Stępak, A.J. Antończak, M. Maj, M. Gazińska, B. Kryszak, J. Pigłowski
In the article, we present the surface modification method of poly(l-lactide)/hydroxyapatite hybrid material using ultrashort pulse/femtosecond laser for tissue engineering application. Using femtosecond laser ablation we obtained 3D grooved structures at the composite surface with precisely controlled dimensions having 50–100 μm in width and a depth of 20 μm with porous bottom. Differential scanning calorimetry and XRD showed no significant influence of laser process on the supramolecular structure of the polymer in composite after modification. ATR analysis revealed partial surface “amorphisation” due to extremely high temperature gradient provided by laser pulses and relatively long crystallization time of PLLA. GPC revealed decrease in molecular weight of PLLA in the composite after laser modification. In addition biological tests were conducted. Human osteoblasts ATCC CRL-11372 were cultured on the laser-modified surface. Cytotoxicity and real time cell growth experiments showed no toxic effects of laser treated material on cells. This implies that femtosecond laser surface treatment is a promising method which potentially can be used in tissue engineering for scaffold modification and facilitating integration of bioresorbable implant and bone.
Ultra-low phosphorus loading to achieve the superior flame retardancy of epoxy resin Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-31 Junling Wang, Chao Ma, Peilong Wang, Shuilai Qiu, Wei Cai, Yuan Hu
A novel phosphorus-containing compound (DOPO-THPO) is synthesized via the Atherton-Todd-reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and trihydroxymethylphosphine oxide (THPO), and then employed as flame retardant for diglycidyl ether of bisphenol A/4-4 diaminodiphenylmethane epoxy resin (DGEBA/DDM). Based on the ultra-low phosphorus loading, the highly efficient flame retarded epoxy resin (EP) systems are successfully established in this work. Remarkable improvements in the limited oxygen index (LOI) values and UL-94 rating of flame retarded EP systems are observed. In detail, when the phosphorus content is only 0.33 wt%, the EP composite receives V-0 rating in the UL-94 vertical burning test with LOI value of 30%. Heat release of EP composites is obviously inhibited with the formation of intumescent char residue. Furthermore, TG-IR result of DOPO-THPO shows the generation of phosphorus containing products, which may provide a gaseous phase flame retardant function on EP. This work may open the new door for the construction of highly efficient flame retardant EP system based on the ultra-low phosphorus loading.
Influence of Zeolitic imidazolate framework-8 on the thermal stabilization of poly(vinyl chloride) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-31 Mei Wang, Xianghai Song, Jianchun Jiang, Jianling Xia, Mei Li
Enhanced polymer degradation of polyethylene and polypropylene by novel thermophilic consortia of Brevibacillus sps. and Aneurinibacillus sp. screened from waste management landfills and sewage treatment plants Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-31 Sinosh Skariyachan, Amulya A. Patil, Apoorva Shankar, Meghna Manjunath, Nikhil Bachappanavar, S. Kiran
The current study prioritizes the polymer degradation potential of novel thermophilic consortia of Brevibacillus sps. and Aneurinibacillus sp. screened from sewage treatment plants and waste management landfills for low and high density polyethylene (LDPE, HDPE) and polypropylene (PP) films and pellets. The screening of 36 plastic-degrading isolates was carried out and degradation abilities were studied for 140 days. The eight isolates that showed highest percentage degradation were combined in various possible combinations to study the degradation efficiency. Among them, the combination of IS1, IS3, ISA and ISC demonstrated highest percentage weight reduction for three forms of plastic which was selected for further degradation study at varying temperature conditions. The biodegradation end products post 140 days were studied by Fourier infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), nuclear magnetic resonance (NMR) and gas chromatography-mass spectroscopy (GC-MS). The isolates were characterized by 16S rDNA gene sequencing and secondary structures of 16S rDNA were predicted. The highest percentage weight reduction for LDPE, HDPE and PP strips treated with the consortia of four isolates was determined to be 58.21 ± 2, 46.6 ± 3 and 56.3 ± 2% respectively and LDPE, HDPE and PP pellets that were treated with consortia was determined to be 45.7 ± 3, 37.2 ± 3 and 44.2 ± 3% respectively (p ≤ 0.05) at 50 °C in comparison with other combinations and varying temperatures. FTIR analysis of the plastic film post 140 days showed that the presence of new adsorption bands. SEM and AFM analysis revealed that biofilm formation and structural variations on the treated plastic strips and EDS analysis suggested significant reduction in percentage weight of carbon content. NMR analysis suggested the appearance of methyl and aldehyde moieties and GC-MS analysis revealed fatty acid end-products. IS1, IS3, ISA and ISC were found to be four novel strains and were designated as Aneurinibacillus aneurinilyticus btDSCE01, Brevibacillus agri btDSCE02, Brevibacillus sp. btDSCE03 and Brevibacillus brevis btDSCE04 respectively. The study suggested that these novel thermophilic consortia can be scaled up as potential inoculums for the enhanced biodegradation of polyethylene and polypropylene derivatives in plastic wastes.
The effects of POSS particles on the flame retardancy of intumescent polypropylene composites and the structure-property relationship Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-02-01 Gizem Turgut, Mehmet Dogan, Umit Tayfun, Guralp Ozkoc
Chemical recycling of poly(lactic acid) by water-ethanol solutions Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-17 Fabiola Iñiguez-Franco, Rafael Auras, Kirk Dolan, Susan Selke, Daniel Holmes, Maria Rubino, Herlinda Soto-Valdez
A propane burner test for passive fire protection (PFP) formulations containing added halloysite, carbon nanotubes and graphene Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-17 A.G. Gibson, W.N.B. Wan-Jusoh, G. Kotsikos
Passive fire protection materials (PFP) have been characterised quantitatively using a constant heat flux propane burner test, with the PFP attached to a steel substrate. The burner test was able to produce a large, constant heat flux, to simulate a severe fire condition. The heat transferred through the PFP was calculated from the temperature rise of the steel. A simplified model is discussed, to account for different combinations of substrate thickness, PFP thickness, heat flux and exposure time. It was found that, despite the complex processes of resin decomposition and intumescence, heat transmission could be modelled, to a reasonable approximation, by treating the PFP as a material with single point values of apparent thermal diffusivity and conductivity. This leads to an equation that can be used to characterise PFPs and indeed to specify their required thickness. The burner test was employed to interpret the effects of adding small quantities of three nano-materials: halloysite nanotubes (HNT), multi-walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GNP), to a standard PFP formulation. It was found that HNT addition resulted in a significant performance improvement, whereas the other nano-materials did not produce an improvement.
Effect of carbon black distribution on the properties of polyethylene pipes part 1: Degradation of post yield mechanical properties and fracture surface analyses Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-11 Suleyman Deveci, Nisha Antony, Birkan Eryigit
In this study, we investigated the effect of carbon black distribution on the degradation of mechanical properties of high-density polyethylene in the form of plastic pipes used in water distribution networks. Polyethylene pipes with similar carbon black concentrations but different carbon black distributions were produced with industrial scale compounding and extrusion equipment. Tensile specimens were directly prepared from extruded pipe samples and elongated to fracture at different strain rates. Carbon black distributions of bulk samples and fracture surfaces were investigated using stereo and scanning electron microscopy (SEM). It was found that the carbon black distributions, fracture surfaces and fracture modes were significantly different in these pipes. Although the yield properties were similar, the post-yield properties of samples were significantly different, dramatically decreasing with the increasing inhomogeneity of carbon black distribution. Pipes with a certain level of heterogeneity in the carbon black distribution showed ductile and brittle fractures in the same fracture plane, whereas homogenous black and natural polyethylene (without carbon black) showed ductile fractures only.
Coupled aging effects in nanofiber-reinforced siloxane foams Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-11 Andrea Labouriau, Tom Robison, Drew Geller, Carl Cady, Adam Pacheco, Jamie Stull, Joseph H. Dumont
This study investigates the combined effects of ionizing radiation and thermal treatments on the aging of siloxane foams containing small amounts of carbon nanofibers. Our siloxane foams were exposed to accelerated aging conditions for more than two years, resulting in very low dose rates. In addition, foams were aged under compressive load to evaluate the strength of the porous microstructure. Samples were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), Mössbauer, mass spectroscopy, electron paramagnetic resonance spectroscopy (EPR), solvent swelling, imaging techniques, uniaxial compressive load testing and tear testing. No significant changes in thermal stability or chemistry of the accelerated aged foam were observed, although gas evolution was detected. Changes in crystallization levels at low temperatures, microstructure, and mechanical properties were observed for foams with and without carbon nanofibers. In particular, foams aged under compressive load showed irreversible deformation of the porous microstructure. This study demonstrates that aging effects were enhanced when thermal and radiolysis were coupled together and that the addition of carbon nanofibers did not improve aging effects.
Crystallization kinetics of polylactide: Reactive plasticization and reprocessing effects Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-09 Berit Brüster, Antonio Montesinos, Pauline Reumaux, Ricardo A. Pérez-Camargo, Agurtzane Mugica, Manuela Zubitur, Alejandro J. Müller, Philippe Dubois, Frédéric Addiego
This work focused on the determination of crystallization kinetics of neat polylactide (PLA) and a plasticized grade of PLA obtained by reactive extrusion (pPLA), as a function of thermomechanical recycling. In particular, the materials were submitted to repeated extrusion and injection procedures to simulate recycling. Prior reprocessing, spherulitic growth rate determined by polarized light optical microscopy indicated that pPLA crystallized into much smaller spherulites as compared to PLA. This finding was explained by a lower nucleation energy barrier promoted by the plasticization of pPLA. Isothermal overall crystallization kinetics were determined by differential scanning calorimetry measurements. It was found that pPLA crystallized much faster than neat PLA due to the plasticization effect. With increasing the number of processing cycles up to 5, PLA crystallization rate gradually increased, while at the same time that of pPLA remained constant. This result was explained by more important degradation mechanisms in PLA as compared to pPLA that enhanced chain mobility, as shown by molecular weight measurements. Moreover, pPLA had a very high initial chain mobility that is maintained regardless of the number of processing cycles. However, the final crystallinity degree was lower in reprocessed pPLAs, as grafting and cross-linking reactions produced during reactive extrusion interrupt crystallizable linear crystallizable sequences and reduced the amount of crystals formed.
The anaerobic biodegradation of poly(lactic) acid textiles in photosynthetic microbial fuel cells: Self-sustained bioelectricity generation Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-09 Xiang Qi, Yi Bo, Yiwei Ren, Xingzu Wang
Poly(lactic) acid (PLA) is a promising material due to the complete biodegradability and environmental-friendly characteristics, but it is difficult to decompose by traditional anaerobic composting. Photosynthetic microbial fuel cells (MFC) are envisaged as a potential bioenergy harvesting techniques in recent years. In this work, the anaerobic biodegradation of PLA textiles for bioelectricity generation was explored in a dual chamber MFC devices using the hybrid anoxygenic photosynthetic bacteria (APB). The result showed that the surface of PLA textiles appeared the widespread damage by SEM micrographs observation, and the corresponding weight loss was 26.67%. The analysis of FT-IR suggested that the breakage process was a biochemical action due to the function of depolymerase. Meanwhile, a stable current density generation of 4.4 ± 0.2 mA/cm2 (500 Ω external resistor) at PLA textiles concentration of 1 g/L was obtained under the shortage of other carbon sources. However, the microbial community structure was obvious difference before and after the test. Moreover, the exploration will provide more potential information for self-sustained bioelectricity generation of MFC.
Transparent and soluble polyimide films from 1,4:3,6-dianhydro-D-mannitol based dianhydride and diamines containing aromatic and semiaromatic units: Preparation, characterization, thermal and mechanical properties Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-09 Zhiming Mi, Zhixiao Liu, Jianan Yao, Chunbo Wang, Changjiang Zhou, Daming Wang, Xiaogang Zhao, Hongwei Zhou, Yumin Zhang, Chunhai Chen
To develop colorless and soluble polyimide films, a novel dianhydride containing 1,4:3,6-dianhydro-D-mannitol unit, 2,5-bis(3,4-dicarboxyphenoxy)-1,4:3,6-dianhydromannitol dianhydride (IMDA) was synthesized. And two series of polyimides were prepared via a two-step thermal imidization, PI−(1−4) were obtained from IMDA and four kinds of aromatic diamines while PI−(5−7) from IMDA and three kinds of semiaromatic diamines. All the polyimides were readily soluble in common polar solvents and could afford flexible, tough and colorless films with transparency up to 89% at 450 nm. Especially, polyimides simultaneously containing 1,4:3,6-dianhydrohexitol units in diamine and dianhydride exhibited comparable optical and soluble performance with the alicyclic fluorinated ones. Meanwhile, it was certified that 1,4:3,6-dianhydrohexitol fragment in dianhydride was more determinant in solubility and transmittance of polyimides than that in diamine. An overall investigation of these polyimides on thermal, mechnical, morphological, soluble, optical and dielectric properties was presented, and their structure-property relationships were discussed in detail.
Effect of ZnO particle sizes on thermal aging behavior of natural rubber vulcanizates Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-08 Yong Hwan Lee, Misuk Cho, Jae-Do Nam, Youngkwan Lee
The effects of ZnO particle size on crosslinking and thermal aging behavior of natural rubber (NR) were investigated. NR vulcanizates filled with nano ZnO allowed higher crosslink density, lower polysulfide crosslink, and stronger mechanical properties than those filled with micro ZnO. After thermal aging, NR filled with nano ZnO exhibited much more stable chemical and mechanical properties. The high crosslink density as well as the formation of more stable mono- and di-sulfidic crosslinks was attributed to the good dispersion and high surface area of the nano ZnO.
Key role of magnesium hydroxide surface treatment in the flame retardancy of glass fiber reinforced polyamide 6 Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-08 M. Casetta, G. Michaux, B. Ohl, S. Duquesne, S. Bourbigot
In this paper, the fire retardant properties of two magnesium dihydroxide (MDH) were compared into glass fiber reinforced polyamide 6 (PA6 GF). The difference between the additives lies in the presence of a vinylsilane treatment at the surface of one of the two MDH (H5A grade) whereas the other is a non-treated MDH (H5 grade). The investigations showed that better fire properties were obtained with PA6 GF/H5A formulation compared to the PA6 GF/H5 one. More precisely, a higher UL-94 rating, a higher glow wire ignition temperature (GWIT) and a higher time to ignition (TTi) at the mass loss calorimeter (MLC) were obtained. To understand the differences between H5 and H5A in terms of fire performances, the mechanisms of degradation of the two fire retarded (FR) formulations was investigated, analyzing both the gas phase and the condensed phase. A significant part of the study was also devoted to the characterization of the ceramic protective layer formed thanks to the use of MDH. The analysis of the gas phase revealed that the degradation products of the two FR formulations were similar. Moreover, as shown by the condensed phase analysis, no chemical reaction occurs between PA6 and H5 or H5A, proving that the MDH surface treatment was not involved in chemical reactions during the processing of the formulation or its degradation. On the contrary, the main differences between the two formulations concern the properties of protective layer formed during the degradation. It was shown that the silane treatment and the MgO formed during MDH dehydration lead to the formation of a cohesive structure between the glass fibers when the material degrades, resulting in a highly insulating and resistant protective layer.
Highly efficient flame-retardant glass-fiber-reinforced polyamide 6T system based on a novel DOPO-based derivative: Flame retardancy, thermal decomposition, and pyrolysis behavior Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-08 Weijiang Huang, Wentao He, Lijuan Long, Wei Yan, Min He, Shuhao Qin, Jie Yu
A novel bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative (PN-DOPO) was used to fabricate a flame-retardant glass fiber-reinforced polyamide 6T (GFPA6T). The effects of PN-DOPO on the flame retardancy, thermal decomposition, and pyrolysis behavior of GFPA6T was systematically investigated, compared to neat GFPA6T and its composite flames retarded by aluminium diethylphosphinate (OP1230). The flame retardancy, thermal stabilities, and burning behaviors of the composites were evaluated by vertical burning test (UL-94), limiting oxygen index (LOI), thermogravimetric analysis (TGA), and cone calorimeter test. Moreover, the flame-retardant mechanism was analyzed by pyrolysis-gas chromatograph/mass spectrometer (Py-GC/MS), Fourier transform infrared coupled with the thermogravimetric analyzer (TG-FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Results reveal that the modified GFPA6T, with the addition of 15 wt% PN-DOPO, achieves a V-0 rating and LOI value of 28.9%, whereas introducing OP1230 at levels up to 17.5 wt% can achieve a V-0 rating and LOI value of 40.1%. The superior flame retardancy for GFPA6T/PN-DOPO system can be attributed to two factors as follows: the release of pyrolytic gases containing phosphorus-based aromatic structures and nonflammable gases at the early stage, thereby playing an important role in the gas phase, and the formation of char layer consisting of phosphorus-containing char layer and polyaromatic structures in the condensed phase. In comparison, diethyl-phosphorus oxides and their derivatives are detected in the gas phase for GFPA6T/OP1230 samples, and the residues consist of aluminum phosphorus oxides, polyphosphates, and a slight amount of charred polymer.
Control of the secondary crystallisation process in poly(hydroxybutyrate-co-hydroxyvalerate) through the incorporation of poly(ethylene glycol) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-05 Catherine A. Kelly, Annabel V.L. Fitzgerald, Mike J. Jenkins
Poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-co-HV) is a sustainable and biodegradable polymer, but as a potential packaging material, it suffers from a narrow processing window and embrittlement over time due to secondary crystallisation. This study aims to extend previous research by exploring the effect of the addition of poly(ethylene glycol) (PEG), in a range of molecular weights and compositions, on the rate of embrittlement. On blending, it was apparent that there was a reduction in both the melting point (of up to 7 °C) and the melt viscosity. Furthermore, there was a reduction in both the modulus and tensile strength indicating that PEG acts as an effective plasticiser in PHB-co-HV. In terms of the secondary crystallisation process, the addition of PEG could not prevent the process from occurring, only hinder it. PEG 600 in relatively high concentrations was found to be the most effective in this regard with a 53% reduction in the change in Young's modulus compared to pure PHB-co-HV. This observation, together with the melting point reduction which extends the processing window for PHB-co-HV, makes PEG a worthwhile additive to an otherwise fundamentally brittle polymer.
Exterior and under glass natural weathering of hemp fibers reinforced polypropylene biocomposites: Impact on mechanical, chemical, microstructural and visual aspect properties Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-04 Célia Badji, Joana Beigbeder, Hélène Garay, Anne Bergeret, Jean-Charles Bénézet, Valérie Desauziers
This work aims to investigate exterior and under glass weathering representing decking and car interior end uses of hemp fibers reinforced polypropylene (PP) biocomposites. For this reason, mechanical flexural tests were firstly performed. Then, the evolution of the PP matrix microstructure was determined through Differential Scanning Calorimetry (DSC). The chemical composition was studied by infrared spectroscopy to understand the photo- and thermo-chemical mechanisms. CIELab system-based colorimetric measurements were carried out to determine the evolution of the chromaticity and lightness. Through a new approach, gloss was obtained by determining the type of reflection of materials as either specular or diffuse, and the surface aspect was characterized by rugosimetry. The influence of the rate of hemp fibers (from 0 to 30 wt%) was studied. Results showed that biocomposites were generally more sensitive than neat PP whatever the weathering conditions. However, each type of weathering assessment allowed understanding the contribution of each degradation factor. Indeed, rainfall or UV-A rays induced an increase in the vinyl concentration and the formation of cracks on the surface whereas the carbonyl functional groups rate was not influenced by the type of weathering. The high temperatures under windshield glass favored a chemicrystallization and biocomposites yellowing at the first period of exposition whereas outdoor exposure induced red color loss.
Correlation between artificial and natural weathering of hemp fibers reinforced polypropylene biocomposites Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2018-01-04 Célia Badji, Joana Beigbeder, Hélène Garay, Anne Bergeret, Jean-Charles Bénézet, Valérie Desauziers
The degradation behaviors of hemp fibers reinforced PP biocomposites under outdoor and artificial weathering were compared to establish a correlation. For this purpose, several measurements were performed throughout the expositions. Mechanical performance was tested by three-point bending test. Microstructure and chemical composition changes were also assessed. Otherwise, visual aspect and topography were determined. The artificial weathering effectively accelerated the degradation mechanisms. Oxidation pathways and surface aspect alteration of both polymer and biocomposites occurred faster. However, whereas biocomposites were mainly subjected to outdoor conditions due to high sensitivity of hemp fibers, neat PP was globally mostly affected by laboratory chamber conditions. Its oxidation rate largely outstripped reinforced materials ones. Principal Component Analysis was used for verifying the differences of variables correlations profiles between artificial and exterior ageing dataset in order to compare the degradation mechanisms. Through the statistical analysis, some attempts were made to find equivalence between artificial and outdoor weathering times thanks to properties degradation rate similarities.
Identification of antioxidants in polymeric insulating materials by terahertz absorption spectroscopy Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-18 Takuya Kozai, Takuya Kaneko, Naoshi Hirai, Yoshimichi Ohki
For the purpose of using organic polymeric materials for electrical insulation, various additives such as antioxidants are added to prevent degradation or oxidative decomposition of the polymers. Therefore, it is desirable that we can identify antioxidants added in polymers by instrument analyses. In this research, terahertz absorption spectroscopy was conducted for nine kinds of antioxidants. The spectroscopy was also conducted for sheets of low-density polyethylene, to which each antioxidant had been added with different contents. As a result, it has become clear that each antioxidant has its own specific spectrum. In addition, for most antioxidants, the absorption intensity is proportional to the content of antioxidant added in LDPE. However, several absorption peaks change their spectral shapes when the antioxidant is in LDPE.
Weathering resistance of PMMA/SiO2/ZrO2 hybrid coatings for sandstone conservation Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-16 Laura Bergamonti, Federica Bondioli, Ilaria Alfieri, Silvia Alinovi, Andrea Lorenzi, Giovanni Predieri, Pier Paolo Lottici
Accelerated weathering of polymethylmethacrylate (PMMA) and of hybrid PMMA/SiO2/ZrO2 films was monitored by spectroscopic, thermal and colorimetric measurements. The hybrid polymers were obtained by sol-gel process adding tetraethylorthosilicate (TEOS) and zirconyl chloride (ZrOCl2*8H2O) to a solution of PMMA. Photo ageing tests on polymeric films under artificial sunlight irradiation in a climatic chamber suggest that the addition of the inorganic fillers slows down the chemical degradation of PMMA. The polymers were deposited on two different sandstones from Tuscany (Italy): Pietra Dorata and Pietra Serena. Capillary water absorption, contact angle and color measurements show that the hybrid-PMMA coatings retain the water repellency of the sandstone and do not introduce noticeable changes of the aesthetic appearance. Accelerated weathering of the treated sandstone confirms that the SiO2/ZrO2 inorganic filler delays the chromatic changes of the polymer. The hybrid coating may then be proposed for application in the field of outdoor conservation of sandstones, used as building material in ancient and modern architectures.
Plasma induced degradation and surface electronic structure modification of Poly(3-hexylthiophene) films Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-14 Marinos Tountas, Dimitra G. Georgiadou, Angelos Zeniou, Kostas Seintis, Anastasia Soultati, Ermioni Polydorou, Spyros Gardelis, Antonios M. Douvas, Thanassis Speliotis, Dimitris Tsikritzis, Stella Kennou, Mihalis Fakis, Evangelos Gogolides, Dimitris Tsoukalas, Panagiotis Argitis, Maria Vasilopoulou
Plasma treatment is an environmentally friendly solution for modifying or nanostructuring the surface of several materials including photoactive polymers. The detailed characterization of the effect of plasma treatment on chemical and optoelectronic properties of photoactive polymers is, therefore, of specific interest. Herein, the effect of the exposure of poly(3-hexylthiophene) (P3HT) thin films to plasma created in three different gases (oxygen, argon and hydrogen) was studied. A range of spectroscopic techniques, such as x-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy in conjunction with UV–vis absorption, Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopies, are employed to quantify the extent of chemical modification occurring in each particular case. It is shown that oxygen plasma treatment leads to the disruption of the π-conjugation via the direct oxidation of the sulfur atom of the thiophene ring while the aliphatic side chain remains nearly unaffected. An oxidation mechanism is proposed according to which the sulfur atom of the thiophene ring is oxidized into sulfoxides and sulfones, which subsequently degraded into sulfonic esters or sulfonic acids in a relatively small degree. For argon and hydrogen plasma treatments some oxidation products are detected only at the polymer surface. In all cases the polymer surface Fermi level is shifted closer to the highest occupied molecular orbital (HOMO) energy after plasma treatment indicating p-type doping arising from surface oxidation.
Biodegradation rate of biodegradable plastics at molecular level Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-13 Selene Chinaglia, Maurizio Tosin, Francesco Degli-Innocenti
Plastics are solid materials where biodegradation happens on the surface. Only the surface is affected by biodegradation while the inner part should not be readily available for biodegradation. Thus, at a laboratory level, the biodegradation rate is expected to be a function of the surface area of the tested sample. The higher the surface area, the higher the biodegradation rate, all other environmental conditions being equal. In order to further explore the role of particle size on biodegradability, plastic pellets of polybutylene sebacate were milled and sieved into different particle sizes, thus obtaining four samples, pellets included, with different specific surface areas (33, 89, 193, and 824 cm2g-1). The surface areas were assessed through direct measurement (pellets) or a theoretical estimation followed by an image analysis. The different samples were tested for biodegradation in soil for 138 days. The rates calculated with a linear regression in the first part of the biodegradation process were related to the respective total available surface area. The data are well described by a linear regression of the double reciprocal plot (the Lineweaver-Burk approach used in enzymatic kinetics) that enables the estimation of the theoretical maximum biodegradation rate (kmax = 97 mg Cpolymer day−1). The kmax can be considered as an estimation of the biodegradation rate at molecular level, when the available surface area is not limiting biodegradation. An additional hypothesis is that the same polymer tested in soils with different microbial loads would display different kmax. The Michaelis constant (Km), i.e. the surface area at which the reaction rate k is half the maximum rate, is 1122 cm2. It is remarkable to notice that if polybutylene sebacate could be tested in a nanopolymeric form, it could very likely satisfy the Organization for Economic Co-operation and Development (OECD) criteria of “ready biodegradability” for chemicals (e.g. 60% biodegradation in a 10-day window within a 28-day test). This is the first time that the biodegradation kinetics of a solid polymer have been estimated by using the Michaelis-Menten approach.
Application of ammonia pretreatment to enable enzymatic hydrolysis of hardwood biomass Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-12 Kiyoshi Sakuragi, Kiyohiko Igarashi, Masahiro Samejima
Ammonia pretreatment greatly improves enzymatic hydrolysis of grass biomass, but is reported to be ineffective for hardwood biomass. Here, we examined the effectiveness of ammonia pretreatment of biomass from six hardwood species with different contents of xylan and lignin. Ammonia pretreatment greatly improved enzymatic hydrolysis of polysaccharides in birch and willow, but was less effective for acacia, eucalyptus, and poplar. The effectiveness of ammonia pretreatment increased with xylan content but decreased with lignin content of the hardwood species. By adding a recombinant xylanase to the commercial enzyme digestion cocktail, the yield of enzymatic hydrolysis of ammonia-pretreated birch biomass was improved to a similar level to that obtained with grass biomass. Our results indicate that enzymatic hydrolysis of biomass from hardwood species having a relatively high xylan/lignin ratio can be achieved with a xylanase-enriched enzyme cocktail after ammonia pretreatment.
Methanolysis of microbial polyester poly(3-hydroxybutyrate) catalyzed by Brønsted-Lewis acidic ionic liquids as a new method towards sustainable development Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-11 Xiuyan Song, Fusheng Liu, Hui Wang, Chan Wang, Shitao Yu, Shiwei Liu
Chemical recycling of bio-based polymer poly(3-hydroxybutyrate) (PHB) by methanolysis was discussed in detail from the perspective of biological refining. The results of methanolysis transformed PHB into ester monomer successfully by using some ionic liquids. PHB was depolymerized into methyl 3-hydroxybutyrare (M3HB) at lower degradation temperatures in the presence of Brønsted-Lewis acidic ionic liquid 1-(3-sulfonic acid)-propyl-3-methylimidazole ferric chloride ([MIMPS]FeCl4 as catalyst. Obtained M3HB from this reaction can be used in many areas, which is consistent with the principles of sustainable development. Then, the influences of reaction parameters on PHB methanolysis were investigated and the optimum conditions were obtained. Under the optimum conditions, the conversion of PHB and yield of M3HB was 98.5% and 87.4%, respectively. This catalyst could be recycled up to 6 times with no apparent decrease in catalytic activity. At the same time, the methanolysis mechanism of PHB is proposed through the experiments. In addition, kinetic study indicated that this reaction was pseudo-first-order reaction with activation energy of 24.74 kJ/mol.
Effect of styrene butadiene rubber on the light pyrolysis of the natural rubber Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-06 Pan Song, Xiaoyu Wu, Shifeng Wang
The use of styrene butadiene rubber (SBR) in tire rubber presents a challenge for the recycling of tire rubber because of its complex degradation behavior compared with that of natural rubber (NR). The effect of the composition of SBR on the degradation of NR was observed by light pyrolysis at variable times at 300 °C. The morphology, sol-gel evolution of the NR/SBR blends and the degradation mechanism was investigated. In addition, the structural evolution of the sol and gel fractions were measured by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The results indicated that the mechanism of degradation between SBR and NR differed significantly at 300 °C. The broken molecular chains present in SBR recombined with themselves or those of NR to form a new crosslinked network. The results also showed that the ratio of NR/SBR in the sol and gel fractions remains almost constant and unrelated to the original ratio of the NR/SBR blends. Following an increase in SBR content, the sol fraction of different NR/SBR blends mainly consisted of the small molecular chains of NR, whereas the gel fraction mostly constituted re-crosslinked SBR molecular chains.
The effect of de- and re-polymerization during heat-treatment on the mechanical behavior of Scots pine sapwood under quasi-static load Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-06 Michael Altgen, Tuuli Uimonen, Lauri Rautkari
Loss in strength and ductility is a major drawback for the heat-treatment of solid wood. Previous studies focused mainly on the de-polymerization of cell wall constituents as a cause and the importance of the preferential removal of hemicelluloses. This study tested the hypothesis that the mechanical behavior of wood is additionally affected by re-polymerization reactions within the cell wall matrix during heat-treatment. This was achieved by comparing changes in chemical composition, FT-IR spectra, and mechanical properties of Scots pine sapwood that was heat-treated in either dry state in superheated steam or in wet state using pressurized hot water. Although preferential de-polymerization of hemicelluloses was evident for both heat-treatment techniques, the analysis of the chemical composition and FT-IR spectroscopy indicated additional re-polymerization reactions within the cell wall matrix of dry heat-treated wood. The consequent formation of covalent bonds and cross-links increased the resistance against compression loads and hindered inelastic deformation during bending. This resulted in an additional reduction in bending strength and strain energy density of dry compared to wet heat-treated wood. Re-polymerization reactions during heat-treatments of wood in dry state were suggested as the main cause for the brittle failure under bending loads, while the effect of hemicellulose-removal on brittleness was much smaller than stated previously.
Fire retardant sol-gel coated polyurethane foam: Mechanism of action Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05 S. Bellayer, M. Jimenez, B. Prieur, B. Dewailly, A. Ramgobin, J. Sarazin, B. Revel, G. Tricot, S. Bourbigot
This paper investigates the flame retardant (FR) mechanism of action of a flexible PU foam, flame retarded with a sol-gel coating made of a mixture of tetraethoxysilane (TEOS), methyl triethoxysilane (MTES), 3-amino propyl triethoxysilane (APTES) and diethyl phosphite (DEP) in an ethanol/water solution. To build a mechanism of action, the coating as well as the residues obtained after fire testing were analyzed using solid state nuclear magnetic resonance (NMR), rheology, thermogravimetric analyses coupled with infrared detection (TGA-FTIR), microcalorimetry of combustion (MCC), smoke box and Pyrolysis Gas chromatography coupled with mass spectrometry (Py-GCMS). The coating shows an intumescent behavior upon burning exhibiting significant expansion and bubbling. The expansion occurs in two steps: a first step around 190 °C, related to the release of ethanol, and a second one around 380 °C, related to the release of non-degraded DEP, ammonia and propylene during degradation of the PU matrix. The flame retardant effect occurs (i) in the condensed phase by intumescence, which yields a thermal insulating layer made of a SiO2 and Si-O-P network mixed with orthophosphate at the surface of the PU foam, but also (ii) in the gas phase by the release of non-degraded DEP, which acts as free radical scavenger. The coating allows the protection of the underlying PU foam during burning as well as the reduction of the amount of smoke released.
Multi detection in Size-Exclusion Chromatography of electron beam irradiated Ethylene Norbornene Copolymers Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05 Hala Barakat, Wowro Sonia Rosine Lago, Caroline Aymes-Chodur, Ange Privat Ahoussou, Najet Yagoubi
Ethylene Norbornene Copolymers (ENCs) belong to the Cyclic Olefin Copolymers (COC) family and are used in numerous industrial fields. The goal of this paper is to compare the behavior under electron beam radiation of three grades of ENCs. Several radiation doses have been tested: 25 kGy to simulate sterilization dose and higher doses (75 and 150 kGy) to emphasize the electron beam effect on polymer ageing. By using Triple Detection (Refractometer/Laser Scattering/Viscometer) Size-Exclusion Chromatography, we wanted to study more accurately the evolution of ENCs under radiation than the previous studies available. Thanks to Triple detection, molecular weights were calculated without being dependent of calibration standards, branching was evidenced as the major effect of electron beams on those materials over a dose of 25 kGy, and long chain branching and branching chains frequencies were also calculated. This study focuses on the effect of additive concentration and norbornene (NB) content and a trend has merged: for a same NB content, the higher the phenolic antioxidant concentration, the less crosslinked was the copolymer with the dose. By increasing NB content, radiation effects were minimized.
Intercalation of phosphotungstic acid into layered double hydroxides by reconstruction method and its application in intumescent flame retardant poly (lactic acid) composites Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05 Sheng Zhang, Yongxin Yan, Wenjia Wang, Xiaoyu Gu, Hongfei Li, Jianhua Li, Jun Sun
Phosphotungstic acid is a typical kind of superior catalysts, and it is hardly to intercalate into the layered double hydroxides (LDH) by ion-exchange process because of its low negative charge. In this work, a phosphotungstic acid intercalated MgAl-LDH (PWA-LDH) was prepared by reconstruction method, and it was then introduced into poly (lactic acid) (PLA) resin in association with intumescent flame retardant (IFR) by melt blending to prepare a flame-retardant biodegradable PLA composite. The effects of PWA-LDH on the flame retardancy of PLA composites were characterized by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter test. The results showed that the composite sample containing 18.0 wt% IFR and 2.0 wt% PWA-LDH achieved the maximal LOI value of 48.3%, passed the UL-94 V-0 rating, and significantly decreased the peak heat release rate from 306.3 kW/m2 of neat PLA to 40.1 kW/m2. Thermogravimetric analysis showed that both the thermal stability and the char formation were enhanced. The char morphology observation revealed that PWA-LDH was beneficial to form dense and compact char layers. It was demonstrated that there existed a synergistic effect between IFR and PWA-LDH in promoting the char formation and enhancing the fire resistance.
Long term stabilization of pe by the controlled release of a natural antioxidant from halloysite nanotubes Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05 József Hári, Márk Sárközi, Enikő Földes, Béla Pukánszky
A natural antioxidant, quercetin, was adsorbed on the surface of halloysite nanotubes in various amounts to prepare a controlled release device. The combined additive was added to polyethylene providing antioxidant levels of 250, 500, 750 and 1000 ppm. All polymer samples contained 1000 ppm Sandostab PEPQ phosphonite secondary antioxidant as well. The stabilizing efficiency of quercetin was determined in processing experiments and by accelerated ageing. Quercetin proved to be a very efficient stabilizer of polyethylene. The use of the halloysite nanotube support resulted in more homogeneous dispersion and facilitated the dissolution of the compound in the polymer. Because of the high energy of halloysite surface, the stabilizer adhered to it very strongly and did not dissolve in polyethylene below a critical concentration. The melt stabilization efficiency of quercetin did not decrease in the presence of the halloysite support. The efficiency of long term stabilization decreased somewhat, but halloysite nanotubes pretreated with the stabilizer possessed a controlled release function, ageing was slower in their presence than with separately dispersed components or in the absence of the halloysite.
Influence of oxidation on the dynamics in amorphous ethylene-propylene-diene-monomer copolymer: A molecular dynamics simulation Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05 Weiwang Wang, Yasuhiro Tanaka, Tatsuo Takada, Shinya Iwata, Hiroaki Uehara, Shengtao Li
This work is dedicated to the mechanism underlying the influence of the oxidation on the dynamic and static characteristics of ethylene-propylene-diene monomer (EPDM) copolymer. A molecular dynamics simulation was employed to provide an insight into the effects of oxidation on the micro and macroscopic properties, such as the density and self-diffusion, free volume, glass transition, and chain transition dynamics. The carbonyl product, the chain scission, and the crosslinking in the EPDM were considered. Self-coefficients and radial distribution function were analyzed to achieve the diffusion and the structure of the systems using a 10 ns produce run at an equilibrium (298 K). The temperature dependence of glass transition and the autocorrelation function for internal torsional rotation have been discussed for understanding the chain dynamics and flexibility after aging, such as the relaxation time and the activation energy. It turns out that the introduction of more carbonyl groups suppresses the internal rotation and the conformational transition of the chains, resulting in the decrease of diffusion and less flexibility due to the strong polar interaction. A system associated with short chains after chain scission possesses a low activation energy, indicating a more flexibility of the chains. Furthermore, the crosslinked structure contributes to the weak chain transition of EPDM (higher Tg) and the high modulus (harden). The different molecular dynamics could be derived from the interaction energy and the structures, such as polar and nonbonded interaction. Some aspects of the details of chain rotation are discussed in this paper.
Multi-scale and multi-technical analysis of the thermal degradation of Poly(Ether imide) Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05 Emilie Courvoisier, Yoann Bicaba, et Xavier Colin
The thermal degradation of PEI has been studied in wide ranges of temperature (between 180 and 250 °C) and oxygen partial pressure (between 0.21 and 50 bars). On one hand, the chemical ageing mechanisms have been analysed and elucidated by FTIR spectrophotometry and by differential calorimetry (DSC) on sufficiently thin PEI films (between 10 and 60 μm thickness) to be totally free of the effects of oxygen diffusion. As expected, and by analogy with other aromatic polymers of similar chemical structure, oxidation occurs preferentially on the methyl groups of the isopropylidene unit of the bisphenol A part, thus causing the disappearance of their characteristic IR absorption band at 2970 cm−1 and the growth of a new IR absorption band at 3350 cm−1, attributed to alcohols. In addition, oxidation leads successively to a relative predominance of chain scissions and crosslinking, resulting in a non-monotonic change of Tg. On the other hand, the consequences of oxidation on the elastic properties have been analysed and elucidated by micro-indentation on polished cross-sections of PEI plates of 3 mm thickness. The diffusion control of oxidation leads to the development of profiles of Young's modulus within the sample thickness, which correlate perfectly with the changes in chemical structure determined by FTIR spectrophotometry. However, the increase in Young's modulus in the superficial oxidized layer is not the direct consequence of oxidation but of a physical ageing.
Thermal and mechanical properties of graphene oxide nanocomposite hydrogel based on poly (acrylic acid) grafted onto amylose Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05 Mohammad Taghi Taghizadeh, Reza Abdollahi, Samira Savani
In the present study, a nanocomposite hydrogel was synthesized based on poly (acrylic acid) grafted onto amylose (PAA-g-amylose) which was containing different loadings of graphene oxide (GO) nanosheets. The structural properties of optimized sample were characterized by X-ray analysis (XRD) and Fourier transform infrared spectroscopy (FTIR). The thermal and mechanical behaviors of synthesized hydrogel were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing. XRD and scanning electron microscopy study demonstrates the formation of highly exfoliated GO layers and its homogenous dispersion throughout the polymer matrix with 3 and 5wt% GO. However, the intercalated structure is predominant with 5wt% GO. The homogenous and the strong interaction of the GO layers and the PAA-g-amylose hydrogel matrix induced the significant improvement in thermal and mechanical properties of the nanocomposite hydrogel. The tensile strength and elastic modulus of the nanocomposite hydrogel increased by 124% and 26%, respectively with 3wt% GO loading. The thermal stability improved by 67 °C and Tg shifted higher temperature by 53 °C at 5wt% GO loading, compared to the pristine hydrogel matrix.
The degradability and thermal properties of chiral polyamide-imides synthesized from several L-amino acids: Side group effects Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-05 Ping Li, Fuyan He, Zhizhou Yang, Wenke Yang, Jinshui Yao
Overview of DLO modeling and approaches to predict heterogeneous oxidative polymer degradation Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-02 Adam Quintana, Mathew C. Celina
PEG-based nanocomposite hydrogel: Thermo-responsive sol-gel transition and degradation behavior controlled by the LA/GA ratio of PLGA-PEG-PLGA Polym. Degrad. Stabil. (IF 3.386) Pub Date : 2017-12-02 Midori Kitagawa, Tomoki Maeda, Atsushi Hotta
The sol-gel transition behavior and the degradation behavior of the nanocomposites consisting of laponite clay nanoparticles and poly(D, L-lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(D,L-lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers (laponite/PLGA-PEG-PLGA nanocomposites) were studied changing the LA/GA ratios of the PLGA blocks in the PLGA-PEG-PLGA. The thermo-responsive sol-gel transition at the physiological temperature (25–37 °C) was observed using the PLGA-PEG-PLGA with a high PEG/PLGA ratio of ∼0.8 regardless of the LA/GA ratios (LA/GA: 1.1, 4.0, and 8.8). The decomposition rates of the laponite/PLGA-PEG-PLGA nanocomposites at 37 °C were regulated by adjusting the LA/GA ratios (LA/GA: 1.1, 4.0, and 8.8). Specifically, ∼45% of the weight loss was observed after 10 days of the decomposition for the laponite/PLGA-PEG-PLGA nanocomposites with the LA/GA ratio of 1.1, while ∼30% of the weight loss was observed after 10 days of the decomposition for the laponite/PLGA-PEG-PLGA nanocomposites with the LA/GA ratios of 4.0 and 8.8.
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