The effect of wood composition and compatibilisers on polyethylene/wood fibre composites

[摘要] ENGLISH ABSTRACT: The effects of the macromolecular composition and content of different wood specieson the properties of wood-polymer composites (WPCs) achieved when usingpoly(vinyl alcohol-co-ethylene) (EVOH) as a compatibiliser and linear low densitypolyethylene (LLDPE) as a matrix, were investigated. Four wood different species (A.cyclops (acacia), E. grandis (eucalyptus), P. radiata (pine) and Q. alba (oak)) withdifferent macromolecular composition and contents and average particle lengths wereused. WPCs filled with these species and WPCs filled with the same species butwithout extractives were prepared using 10% wood content and different amounts (0,2, 5, 7 and 10%) of EVOH. An EVOH content of 7% was found to be optimum.Unextracted woods produced WPCs with higher mechanical properties and betterresistance to ultraviolet (UV) degradation, while the extracted woods produced WPCswith lower water absorption (WA) rates and better thermal stability. Use ofunextracted A. cyclops resulted in composites with superior mechanical and thermalproperties compared with the other unextracted species, most probably due to itshigher cellulose and lignin contents and a favourable average wood particle length(0.225 mm). A. cyclops composites also had higher WA and thickness swelling (TS)rates most likely due to the greater number of free hydroxyl groups present in thesecomposites because of higher cellulose content. Composites containing wood specieswith a high lignin and extractive content, such as A. cyclops and Q. alba, exhibitedhigher resistance to UV degradation.Poly(vinyl alcohol-co-ethylenes) (EVOHs) with different ethylene content (27, 32, 38and 44%) and A. cyclops with different particle sizes (180, 250 and 450 ìm) wereused to prepare WPCs with 10% A. cyclops content. The effect of the contact areabetween the A. cyclops particles and LLDPE achieved when using EVOHs ascompatibilisers on the properties of WPCs was also investigated. The greatestimprovements in the mechanical and thermal properties of composites made with A.cyclops with particle size 180 ìm were obtained when EVOH with 44% ethylenecontent was used. The greatest improvements in the composites made with A. cyclopswith particle size 250 ìm were achieved when EVOH with 38% ethylene content wasused. Composites made with A. cyclops with particle size 450 ìm exhibited betterproperties when EVOH with 27% ethylene content was used. All the composites that had better mechanical and thermal properties, also exhibited better compatibility andinterface adhesion.Two successful approaches were used to impart more attractive ecological andeconomical advantages to WPCs. In the first approach, (0, 2, 5 and 7%) degradedLLDPE was used as a compatibiliser in WPCs at levels of 10, 30 and 50% woodcontent. The resulting mechanical properties, such as tensile strength and hardness,thermal and morphological properties of the compatibilised composites were slightlyhigher than those of noncompatibilised composites and virgin LLDPE. Elongation atbreak and impact properties of the compatibilised composites were lower than invirgin LLDPE, but higher than in noncompatibilised composites.In the second approach, polyethylene (PE) and various functionalised polyethylenes(PEs) were synthesised by copolymerising ethylene and 10-undecen-1-ol using asoluble metallocene/methylaluminoxane catalyst at room temperature. Theincorporation of functional groups increased with increasing comonomer content.WPCs with 10 and 30% wood content were prepared. The composites prepared withfunctionalised PEs had better mechanical, thermal and morphogical properties thanthe composites prepared with PE. Composites made with functionalised PE withhigher hydroxyl groups content exhibited better properties than composites made withfunctionalised PE with lower hydroxyl groups content. Composites with 10% woodcontent exhibited better properties and performance than composites with 30% woodcontent.

[发布机构] Stellenbosch University