Investigation of mechanical property, flame retardancy and thermal degradation of LLDPE–wood-fibre composites

doi:10.1016/S0141-3910(03)00268-4

Polymer Degradation and Stability

Volume 83, Issue 2, February 2004, Pages 241-246

https://doi.org/10.1016/S0141-3910(03)00268-4 Get rights and content

Abstract

The mechanical properties, flame retardancy and thermal degradation of linear low density polyethylene (LLDPE)–wood-fibre composites have been investigated. LLDPE–wood-fibre composites were prepared on a two-roll machine. Maleated polyethylene (MPE) was used to improve the mechanical properties of LLDPE–wood-fibre composites. Ammonium polyphosphate (APP) and the mixtures of APP, melamine phosphate (MP) or pentaerythritol (PER) were used as flame retardants. The experimental results demonstrated that MPE enhanced tensile strength and Izod impact of LLDPE–wood-fibre composites, which is in agreement with literature. APP influenced Izod impact of LLDPE–wood-fibre composites, while it scarcely affected tensile strength. It was found that PER could clearly decrease both tensile strength and Izod impact of LLDPE–wood-fibre composites. This is attributed to PER being involved in esterification reactions between wood-fibre and MPE. According to LOI obtained from this work, APP is an effective flame retardant for LLDPE–wood-fibre composites. It was also found that wood-fibre obviously influenced the thermal degradation behaviour of LLDPE. Wood-fibre made the rapid thermal degradation of LLDPE take place earlier, while APP thermally stabilized LLDPE in LLDPE–wood-fibre composite based upon the temperature (T_max) at maximum peak of the thermal degradation. APP decreased initial temperature (T_initial) of thermal degradation, and promoted char formation of the composite. It is suggested that APP can catalyze esterification, dehydration and char formation of wood fibre.

Introduction

Wood–plastics composites (WPC) are known as a new generation of materials for housewares, automotive and construction, etc [1]. They combines the favourable performance and low cost attributes of both wood and plastics. In recent years, they have been developed rapidly, especially in North America. The interface compatibility between wood–fibre and polymers in WPC is a key problem, on which a lot of literature and patents focus [2], [3], [4], [5]. Maleic anhydride grafted polymers, such as maleated polyethylene and maleated polypropylene, are widely used as good compatilizers to improve the mechanical properties. Silicones, fatty acids and elastomers can also be used as compatibizers in wood–plastic composites. However, flame retardancy of WPC is another important topic because of easy flammability of both woodflour (fibre) and plastics, and demands of fire protection in their use.

Ammonium polyphosphate (APP), melamine phosphate and other phosphorus–nitrogen flame retardants are effective flame retardants for wood, and intumescent flame retardants and bromine-containing flame retardants (decabromodiphenyl oxide) are effective flame retardants for polyolefins. This paper reports research on flame retardancy, thermal degradation and mechanical properties of LLDPE–wood-fibre composite treated with flame retardants.

Section snippets

Materials

Linear low density polyethylene (LLDPE) resin (LLDPE-7042) used in this work was produced by Daqing Petroleum Company. Wood-fibre, 150 μm, was offered by Xinglong Wood-fibre Company. Polyethylene grafted with 1% maleic anhydride (MPE) was manufactured by Shanghai Rizisheng Hightech Cooperation. Ammonium polyphosphate (Hostaflam APP 422) by Hoechst AG Company, pentaerythritol (PER) by Beijing Chemical Company, melamine phosphate (MP) by ourselves, and molecular sieve (type A) by Beijing Reagent

Mechanical properties

Table 2 gives mechanical properties of LLDPE–wood-fibre composites, whose components are based on Table 1. Maleated polyethylene (MPE) was used as a compatilizer between wood fibre and LLDPE in the composites. It can effectively enhance tensile strength and Izod impact of LLDPE–wood-fibre composites in comparison of sample 1 and 2 or 3. This result is attributed to esterification reactions between hydroxyl on the wood-fibre surface and anhydride on the polyethylene chain shown in Scheme 1 (1),

Conclusions

The following conclusions can be drawn:

1.
MPE enhances the mechanical properties of LLDPE–wood-fibre composites, such as tensile strength and Izod impact.
2.
APP, as a flame retardant, showed an influence on Izod impact of LLDPE–wood-fibre composites, while it scarcely affected tensile strength.
3.
PER can clearly decrease both tensile strength and Izod impact of LLDPE–wood-fibre composites. This is attributed to involvement of PER in the esterification reactions between wood fibre and MPE.
4.
It was

Acknowledgments

This work is financially supported by the Natural Science Foundation of China (NSFC). Grant No. 30170752.

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Investigation of mechanical property, flame retardancy and thermal degradation of LLDPE–wood-fibre composites

Abstract

Introduction

Section snippets

Materials

Mechanical properties

Conclusions

Acknowledgments

Polym Degrad Stab

Polym Degrad Stab

Polym Degrad Stab

Polym Degrad Stab

Bioresour. Technol.

Modern plastics

Macromol. Mater. Eng.