Enhancing the flame retardancy and UV resistance of polyamide 6 by introducing ternary supramolecular aggregates

doi:10.1016/j.chemosphere.2021.132100

Chemosphere

Volume 287, Part 2, January 2022, 132100

https://doi.org/10.1016/j.chemosphere.2021.132100 Get rights and content

Highlights

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PhA-MEL-MWCNTs was fabricated by grafting melamine and phytic acid on MWCNTs.
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PhA-MEL-MWCNTs improved flame retardancy and light aging resistance of PA6.
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The melt dripping of PA6 was eliminated by 7% PhA-MEL-MWCNTs.
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The mechanical loss of PA6 after UV aging was reduced by PhA-MEL-MWCNTs.
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The potential danger of PA6 in dairy usage was reduced.

Abstract

An integrated multi-functional additive was fabricated by successively grafting melamine (MEL) and phytic acid (PhA) on multiwalled carbon-nanotubes (MWNCTs), and was then applied in PA6 to improve the flame retardancy and light aging resistance of the composite. The limit oxygen index of PA6 composite containing 7 wt% PhA-MEL-MWCNTs was increased to 26.4 from 21.0. The smoke and CO release were significantly reduced by 48% and 88% respectively, and the severe melt dripping of PA6 in burning was eliminated. It is proved that PhA-MEL-MWCNTs can absorb ultraviolet (UV) radiation, and hence significantly reduces the mechanical property loss of the PA6 composite after UV aging. The tensile strength of the aged PA6/7 wt%PhA-MEL-MWCNTs composite sample only decreased by 18.1%, which was significantly lower than the loss rate of the control aged PA6 sample (62.5%). This protocol provides a new opportunity for fabricating long-life flame retardant polyamide composites.

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, NO_x) 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 (P double bond O) 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)

S. Araby et al.
Recent advances in carbon-based nanomaterials for flame retardant polymers and composites
Compos. B Eng.
(2021)
M.A. Batistella et al.
Interactions between kaolinite and phosphinate-based flame retardant in Polyamide 6
Appl. Clay Sci.
(2018)
P. Bracco et al.
Stabilisation of ultra-high molecular weight polyethylene with Vitamin E
Polym. Degrad. Stabil.
(2007)
J. Cheon 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)
A. Diouf-Lewis et al.
Toward greener polyolefins: antioxidant effect of phytic acid from cereal waste
Eur. Polym. J.
(2017)
W. He et al.
Flame retardant polymeric nanocomposites through the combination of nanomaterials and conventional flame retardants
Prog. Mater. Sci.
(2020)
A.R. Horrocks 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)
M. Jagannatham et al.
Tensile properties of carbon nanotubes reinforced aluminum matrix composites: a review
Carbon
(2020)
S. Jin et al.
Phytic acid-assisted fabrication for soybean meal/nanofiber composite adhesive via bioinspired chelation reinforcement strategy
J. Hazard Mater.
(2020)
B. Kirschweng et al.
Natural antioxidants as stabilizers for polymers
Polym. Degrad. Stabil.
(2017)

Y. Liu et al.

Preparation of ammonium polyphosphate and dye co-intercalated LDH/polypropylene composites with enhanced flame retardant and UV resistance properties

Chemosphere

(2021)

M. Lounis et al.

Fireproofing of domestic upholstered furniture: migration of flame retardants and potential risks

J. Hazard Mater.

(2019)

H. Peng et al.

N-P-Zn-containing 2D supermolecular networks grown on MoS2 nanosheets for mechanical and flame-retardant reinforcements of polyacrylonitrile fiber

Chem. Eng. J.

(2019)

C. Pramanik et al.

Molecular engineering of interphases in polymer/carbon nanotube composites to reach the limits of mechanical performance

Compos. Sci. Technol.

(2018)

T. Semba et al.

Polyamide 6 composites reinforced with nanofibrillated cellulose formed during compounding: effect of acetyl group degree of substitution

Compos. Appl. Sci. Manuf.

(2021)

S. Shang et al.

Modification of halloysite nanotubes with supramolecular self-assembly aggregates for reducing smoke release and fire hazard of polypropylene

Compos. B Eng.

(2019)

S. Shang et al.

Facile preparation of layered melamine-phytate flame retardant via supramolecular self-assembly technology

J. Colloid Interface Sci.

(2019)

Y. Shi et al.

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.

(2020)

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¹: Author Contributions: Y. Li and J. Wang contributed equally.

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Enhancing the flame retardancy and UV resistance of polyamide 6 by introducing ternary supramolecular aggregates

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Characterization of PhA-MEL-MWCNTs

Conclusions

Credit author statement

Declaration of competing interest

Acknowledgments

Compos. B Eng.

Appl. Clay Sci.

Polym. Degrad. Stabil.

Compos. B Eng.

Eur. Polym. J.

Prog. Mater. Sci.

Polym. Degrad. Stabil.

Carbon

J. Hazard Mater.

Polym. Degrad. Stabil.

Chemosphere

J. Hazard Mater.

Chem. Eng. J.

Compos. Sci. Technol.

Compos. Appl. Sci. Manuf.

Compos. B Eng.

J. Colloid Interface Sci.

Compos. Appl. Sci. Manuf.