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

Shebani, Anour N. (Stellenbosch : University of Stellenbosch, 2010-12)

Thesis

ENGLISH ABSTRACT: The effects of the macromolecular composition and content of different wood species on the properties of wood-polymer composites (WPCs) achieved when using poly(vinyl alcohol-co-ethylene) (EVOH) as a compatibiliser and linear low density polyethylene (LLDPE) as a matrix, were investigated. Four wood different species (A. cyclops (acacia), E. grandis (eucalyptus), P. radiata (pine) and Q. alba (oak)) with different macromolecular composition and contents and average particle lengths were used. WPCs filled with these species and WPCs filled with the same species but without 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 better resistance to ultraviolet (UV) degradation, while the extracted woods produced WPCs with lower water absorption (WA) rates and better thermal stability. Use of unextracted A. cyclops resulted in composites with superior mechanical and thermal properties compared with the other unextracted species, most probably due to its higher 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 these composites because of higher cellulose content. Composites containing wood species with a high lignin and extractive content, such as A. cyclops and Q. alba, exhibited higher resistance to UV degradation. Poly(vinyl alcohol-co-ethylenes) (EVOHs) with different ethylene content (27, 32, 38 and 44%) and A. cyclops with different particle sizes (180, 250 and 450 ìm) were used to prepare WPCs with 10% A. cyclops content. The effect of the contact area between the A. cyclops particles and LLDPE achieved when using EVOHs as compatibilisers on the properties of WPCs was also investigated. The greatest improvements in the mechanical and thermal properties of composites made with A. cyclops with particle size 180 ìm were obtained when EVOH with 44% ethylene content was used. The greatest improvements in the composites made with A. cyclops with particle size 250 ìm were achieved when EVOH with 38% ethylene content was used. Composites made with A. cyclops with particle size 450 ìm exhibited better properties when EVOH with 27% ethylene content was used. All the composites that had better mechanical and thermal properties, also exhibited better compatibility and interface adhesion. Two successful approaches were used to impart more attractive ecological and economical advantages to WPCs. In the first approach, (0, 2, 5 and 7%) degraded LLDPE was used as a compatibiliser in WPCs at levels of 10, 30 and 50% wood content. The resulting mechanical properties, such as tensile strength and hardness, thermal and morphological properties of the compatibilised composites were slightly higher than those of noncompatibilised composites and virgin LLDPE. Elongation at break and impact properties of the compatibilised composites were lower than in virgin 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 a soluble metallocene/methylaluminoxane catalyst at room temperature. The incorporation of functional groups increased with increasing comonomer content. WPCs with 10 and 30% wood content were prepared. The composites prepared with functionalised PEs had better mechanical, thermal and morphogical properties than the composites prepared with PE. Composites made with functionalised PE with higher hydroxyl groups content exhibited better properties than composites made with functionalised PE with lower hydroxyl groups content. Composites with 10% wood content exhibited better properties and performance than composites with 30% wood content.

AFRIKAANSE OPSOMMING: Die gevolg van die makromolekulere samestelling van verskillende houtspesies op die eienskappe van hout-polimeer saamgestelde materiale (HPS) wanneer poli(viniel alcohol-ko-etileen) (EVOH) as versoeningsmiddel gebruik word saam met linieere lae digtheid poli(etileen) (LLDPE) as matriks is ondersoek. Vier houtspesies (A. cyclops (acacia), E. grandis (eucalyptus), P. radiata (pine) and Q. alba (oak)) met verskillende makromolekulere samestelling and partikelgrootte-verspreiding is gebruik in die studie. HPS materiale is berei met hierdie vesels, beide voor en na ekstraksie van die houtpartikels met onderskeidelik warm water en oplosmiddels (alleen en in kombinasie). In hierdie HPS materiale is 10% hout gebruik en 0, 2, 5, 7 en 10% EVOH. 'n EVOH inhoud van 7% is as optimum bepaal. Houtpartikels voor ekstraksie het HPS materiale met beter meganiese eienskappe en beter weerstand teen UV bestraling, terwyle partikels wat ekstraksie ondergaan het HPS materiale met laer water-absorpsie en beter hitte-stabiliteit to gevolg gehad het. Die gebruik van ongeekstraheerde A. cyclops het samegestelde materiale met die beste meganiese en termiese eienskappe tot gevolg gehad in vergelyking met die ander houtspesies (voor ekstraksie), as gevolg van die hoer sellulose en lignien inhoud van die spesie, sowel as 'n voordelige partikelgrootte-verspreiding. A. Cyclops saamgestelde materiale he took hoer waterabsorpsie (WA) en dikte-swelling (DS) tempos gehad, weens die groter hoeveelheid vrye hidroksielgroepe teenwoording in die materiale, direk in verwantskap met die sellulose-inhoud. Saamgestelde materiale met 'n hoe hoevellheid lignien en ekstraheerbare materiale (A. cyclops and Q. alba) het beter weerstand teen UV-degradasie geopenbaar. Verskillende poli(viniel alkohol-ko-etileen) polimere (EVOHs) met wisselende etileen-inhoud (27, 32, 38 en 44%) en A. Cyclops met verskillende partikel-groottes (180, 250 en 250 µm) is gebruik om HPS materiale met 10% hout te vervaardig. Die gevolg van die kontak-area tussen die houtpartikels en die LLDPE wanneer EVOHs as versoeningsmiddel gebruik is, is ook ondersoek. Die beste verbetering in die meganiese en termiese eienskappe van die saamgestelde materiale met A. cyclops met partikel-grootte 180 µm is gekry met EVOH met 44% etileen-inhoud, terwyl die beste resultate met 250 µm partikels verkry is met 'n EVOH met 38% etileen, en met 27% etileen in die geval van die 450 µm partikels. Twee benaderinge om meer aantreklike ekologiese en ekonomiese eienskappe by die HPS materiale te bewerkstellig was suksesvol. In die eerste geval is gedegradeerde LLDPE as versoeningsmiddel gebruik. Die resulterende meganiese eienskappe van die HPS materiale met LLDPE as versoeningsmiddel was beter as die HPS mateirale daarsonder. Samegestelde materiale met 10, 30 en 50% hout is vervaardig. Die trekverlenging by die breekpunt sowel as die impaksterkte van die HPS materiale was laer as LLDPE alleen, maar beter as die nie-versoende HPS materiale. In die tweede benadering is polietileen (PE) en gefunksionaliseerde PE gesintetiseer deur etileen en 10-undekeen-1-ol te koplimeriseer met ‘n oplosbare metalloseen/metiel alumoksaan katalis. Die hoeveelheid funskionele (OH) groepe is verhoog deur toenemend ekomonommer-inhoud. HPS materiale met 10 en 30% hout is vervaardig. Die saamgestelde materiale met funksionele PE het beter maganiese eienskappe gehad as die met gewone PE. Hoe hoër die hidroksielgroep-inhoud, hoe beter die eienskappe van die HPS materiale, terwyl die materiale met 10% hout beter eienskappe openbaar het as materiale met 30% hout.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/5270
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