Preparation And Properties Of Organo-montmorillonite Modified Wood Flour/Poly(Lactic Acid) Composites

In this study, three kinds of modification processes, namely, the direct blending process, OMMT suspension impregnation process, and two-step in situ synthesis process were used to prepare OMMT modified WF/PLA composites. The effects of the modification processes on physical, mechanical, and thermal properties of the composites were investigated. A comparison among different modifiers by using the two-step in situ synthesis process of WF/PLA composites was made. To investigate the interaction mechanism between OMMT and WF, the WF components were separated and then modified with OMMT. The modified WF components were then added into PLA to make WF components/PLA composites. The main conclusions are summarized as follows:(1) In the direct blending process, the water uptake and thickness swelling rate of OMMT modified WF/PLA composites increased with increasing WF content. However, the flexural strength decreased. At WF content lower than 40wt%, OMMT improved the composites flexural properties. OMMT had synergetic effects with coupling agents to further improve the composites properties. Composite modified with silane at Iwt% OMMT showed the best properties. In compost test, composites containing silane with OMMT content higher than 1.5wt% can completely degrade in 4 month.(2) In the OMMT suspension impregnation process, a kind of stable micronized OMMT suspension was prepared. After treating with OMMT suspension, the hygroscopicity of the WF decreased.0.5% OMMT suspension modified WF/PLA composite showed reduction in water uptake, thickness swelling rate and improvement in flexural properties. However, excessive OMMT (concentration higher than 4%) weakened the interfacial bonding between WF and PLA, finally resulting in decreased properties.(3) In the two-step in situ synthesis process, OMMT can be synthesized inside WF, which reduced the hygroscopicity and polarity of WF. This modification process was more effective in bigger sized WF with better properties of its composites than small sized ones. OMMT had negative effect on thermal decomposition stability of the composites; however, it can improve their thermal deformation stability. Composite modified with 0.5% OMMT showed the best modification effects. The flexural strength of the composite was 75.39MPa, which made the WF as a reinforcing material rather than a filler.(4) OMMT can be synthesized with different kinds of modifiers inside WF. It was found that OMMT entered into and intercalated with WF cell wall. For the effects of different kinds of modifiers on the modification process, didecyl dimethyl ammonium chloride (DDAC) and sodium dodecyl sulfonate (SDS) were the best among all cationic and anionic modifiers, respectively. However, cationic modifiers were more suitable for making high-performance WF/PLA composites.(5) OMMT interacted with the end carboxyl and phenolic hydroxyl groups of amorphous WF constituents. It formed interacted structure in hemicelluloses (HF) and exfoliated structure in lignin (LF). However, OMMT was difficult to penetrate into cellulose (CF). It only gathered on CF surface. WF components had significant influence on the physical and mechanical properties of PLA composites. CF improved the mechanical properties, water uptake of the composites and resulted in poor dimensional stability. HF had negative effects on almost all properties of the composites. Lignin reduced the water uptake of the composites, thus improved dimensional stability, but has negative effect on mechanical properties.