Enhancing the flame retardancy and UV resistance of polyamide 6 by introducing ternary supramolecular aggregates
Graphical abstract
Introduction
Polyamide 6 (PA6), which is a widely used engineering plastic (Xiao et al., 2021), can be fabricated to fiber, film, and thick products at varied shapes owning to its relative high strength and good melt flow (Semba et al., 2021). Even though the intrinsic strength of PA6 can satisfy most applications, it is susceptible to light, heat, oxygen in service, which gradually decreases the mechanical performances and reduces the service life of end-use products (Ren et al., 2019; Liu et al., 2021; Zhang et al., 2021). In addition, PA6 is flammable and produces a large amount of heat, smoke and also toxic gas (such as HCN, NOx) during combustion. Therefore, the fire safety and service life of PA6 products have attracted much attention in the application of automobile, railway traffic equipment, household electrical appliances and other communal facilities (Batistella et al., 2018; Xu et al., 2018).
In order to improve the fire retardancy of PA6, many kinds of flame retardants were introduced into PA6. Among them, intumescent flame retardants (IFRs) composed of an acid source, a gas source, and a carbon source, have been widely used in PA6 (Horrocks et al., 2012). Generally used IFRs would be decomposed under UV radiation or heating and accelerate the aging of PA substrate, which deteriorates its flame retardancy (Wang et al., 2018; Lounis et al., 2019). Therefore, it is necessary to construct suitable IFR formulations to guarantee comprehensive performance.
Phytic acid (PhA) contains 28 wt % phosphorus, which is an environmentally friendly acid source (Jin et al., 2020), can be used as antioxidants by combining with high thermal stable carriers by ionic bonds (Diouf-Lewis et al., 2017). However, PhA with a starting degradation temperature of 50 °C and a boiling point of 105 °C (Bracco et al., 2007), is not suitable to be melt blended with the polymer.
Melamine (MEL) is often used as a gas source in IFR formulations. It releases a large amount of nonflammable gas during combustion (Xu et al., 2019). In addition, MEL shows anti-aging property for the special triazine ring structure can absorb UV light (Li et al., 2020).
It was also found nanotubes shielded heat and O2 exchange during heating or combustion (He et al., 2020). Nanotubes cannot stop ignition and quench flame propagation (Araby et al., 2021), but reduce the smoke and toxic gases release through adsorption in combustion. The char supported by nanotubular particles acts better as a shield to protect the substrate (Zhang et al., 2018; Shi et al., 2020). However, the nanotubes are easy to agglomerate in the matrix, resulting in the deterioration of mechanical properties. It was found the evenly distributed nanotubes can effectively strengthen the matrix (Ren et al., 2021; Jagannatham et al., 2020; Zhao et al., 2018). Therefore, reasonable surface treatment for nanotubes is generally adopted to reduce their aggregation (Pramanik et al., 2018).
Supramolecular aggregate is usually fabricated from molecules containing different charges by noncovalent bonding (Peng et al., 2019; Shang et al., 2019a). In this work, a multifunctional supramolecular aggregate was prepared by grafting MEL on multiwalled carbon nanotubes (MWCNTs) by ionic interaction, followed by reacting with PhA by π-π stacking. The prepared PhA-MEL-MWNCTs were applied in PA6 to improve the flame retardancy, light resistance, and mechanical properties of the composite.
Section snippets
Materials
Polyamide 6 (PA6, MFI = 100 g/10min) was provided by Maoming Petrochemical Co., Ltd (Guangdong, China). Multi-walled carbon nanotubes (MWCNTs) with a diameter of 30–50 nm were received from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Mela-mine (MEL) was purchased from Macklin Biochemical Co., Ltd. (Shanghai, China). Phytic acid (70 wt % aqueous solution) solution was provided by Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). 98% H2SO4 and 68% HNO3 were obtained from
Characterization of PhA-MEL-MWCNTs
The FTIR spectra of MWCNTs, MEL, PhA, and PhA-MEL-MWCNTs were shown in Fig. 2 (a). One can see the special bands of MEL at 1647, 1546, and 1436 cm−1 (Sun et al., 2020), and the characteristic bands of PhA at 1048 cm−1 (PO) and 998 cm−1 (P–O) in the spectra of PhA-MEL-MWCNTs. It was indicated both PhA and MEL have been grafted on MWCNTs.
The thermal behavior of MWCNTs, MEL, and PhA-MEL-MWCNTs under N2 was traced by TGA. As shown in Fig. 2 (b), MWCNTs showed relatively low mass loss with about 91%
Conclusions
An integrated multi-functional additive PhA-MEL-MWCNTs was successfully prepared by grafting phytic acids and melamine on MWCNTs. It was demonstrated that PhA-MEL-MWCNTs significantly improved the flame retardancy and UV resistance of the PA6 composite. The introduction of 7% PhA-MEL-MWCN into PA6 increased the LOI value to 26.4 from 21.0, improved the UL-94 grade to V-0 without any dripping, and significantly reduced the heat and smoke release. After 150 h UV radiation, the tensile strength
Credit author statement
Yuchun Li: Conception of experimental ideas; Complete the experiments; Writing - Original Draft. Jinzhao Wang: Conceptualization, Methodology. Assisted complete the experiments: Boqiong Xue: Assisted complete the experiments. Shuheng Wang: Assisted analysis. Peng Qi: Assisted analysis. Jun Sun: Assisted analysis and Investigation. Hongfei Li: Formal analysis. Xiaoyu Gu: Assisted analysis of flame retardancy mechanism; Writing - Review & Editing. Sheng Zhang: Formal analysis, Project
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors would like to thank the National Natural Science Foundation of China (No. 51873005, 21875015and 22075010) for their financial support of this research.
References (36)
- et al.
Recent advances in carbon-based nanomaterials for flame retardant polymers and composites
Compos. B Eng.
(2021) - et al.
Interactions between kaolinite and phosphinate-based flame retardant in Polyamide 6
Appl. Clay Sci.
(2018) - et al.
Stabilisation of ultra-high molecular weight polyethylene with Vitamin E
Polym. Degrad. Stabil.
(2007) - et al.
Impact resistance and interlaminar shear strength enhancement of carbon fiber reinforced thermoplastic composites by introducing MWCNT-anchored carbon fiber
Compos. B Eng.
(2021) - et al.
Toward greener polyolefins: antioxidant effect of phytic acid from cereal waste
Eur. Polym. J.
(2017) - et al.
Flame retardant polymeric nanocomposites through the combination of nanomaterials and conventional flame retardants
Prog. Mater. Sci.
(2020) - et al.
Zinc stannate interactions with flame retardants in polyamides; Part 2: potential synergies with non-halogen-containing flame retardants in polyamide 6 (PA6)
Polym. Degrad. Stabil.
(2012) - et al.
Tensile properties of carbon nanotubes reinforced aluminum matrix composites: a review
Carbon
(2020) - et al.
Phytic acid-assisted fabrication for soybean meal/nanofiber composite adhesive via bioinspired chelation reinforcement strategy
J. Hazard Mater.
(2020) - et al.
Natural antioxidants as stabilizers for polymers
Polym. Degrad. Stabil.
(2017)
Preparation of ammonium polyphosphate and dye co-intercalated LDH/polypropylene composites with enhanced flame retardant and UV resistance properties
Chemosphere
Fireproofing of domestic upholstered furniture: migration of flame retardants and potential risks
J. Hazard Mater.
N-P-Zn-containing 2D supermolecular networks grown on MoS2 nanosheets for mechanical and flame-retardant reinforcements of polyacrylonitrile fiber
Chem. Eng. J.
Molecular engineering of interphases in polymer/carbon nanotube composites to reach the limits of mechanical performance
Compos. Sci. Technol.
Polyamide 6 composites reinforced with nanofibrillated cellulose formed during compounding: effect of acetyl group degree of substitution
Compos. Appl. Sci. Manuf.
Modification of halloysite nanotubes with supramolecular self-assembly aggregates for reducing smoke release and fire hazard of polypropylene
Compos. B Eng.
Facile preparation of layered melamine-phytate flame retardant via supramolecular self-assembly technology
J. Colloid Interface Sci.
Simultaneously improved electromagnetic interference shielding and flame retarding properties of poly (butylene succinate)/thermoplastic polyurethane blends by constructing segregated flame retardants and multi-walled carbon nanotubes double network
Compos. Appl. Sci. Manuf.
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Author Contributions: Y. Li and J. Wang contributed equally.