Study On Preparation And Interface Modification Of Rice Straw Fiber/Poly(Lactic Acid) Composites

The biodegradable composites made from natural fibers and biodegradable plastics, which are entirely environmental friendly, are the new focus of study in the new century and have wide application prospects. In this thesis, biodegradable composites consisting of rice straw fiber (RSF) and poly(lactic acid) (PLA) were prepared to achieve improved mechanical and thermal properties by improving interfacial adhesion of composites. The main results were summarized as follows:1. Composites of different content of RSF and PLA were prepared, and a suitable weight ratio of RSF and PLA (RSF filler content was 10% based on composites mass) was chosen to assess the effects of interface compatilizer on interfacial adhesion of composites by HAAKE rheometer. The tensile test and thermogravimetric analysis (TGA) results showed that tensile strength and thermal stability of RSF/PLA composites significantly decreased with an increasing RSF content. Morphological studies by scanning electron microscopy (SEM) demonstrated that poor interfacial adhesion between RSF and PLA. This has been also confirmed by the water absorption test. Moreover, differential scanning calorimetry (DSC) data showed that a little RSF played a role as a nucleating agent and increased the crystallinity degree of the RSF/PLA composites.2. The effect of silane coupling agent species (KH-550, KH-560, KH-570) and content on the interfacial adhesion of the RSF/PLA composites were studied. The maximum tensile strength was obtained when the KH-550 content was 2 wt%(based on RSF mass) by tensile test. Tensile strength of RSF/PLA composites (KH-550,2 wt%) increased by 27.3% compared with the blank sample. It was found that three silane-treated RSF reinforced composites and offered better interfacial adhesion between RSF and PLA by SEM and water absorption test. TGA results confirmed that silane treatment can increase the degradation temperature of the composites. Moreover, DSC data showed that the addition of silane coupling agent can inhibit the PLA from nucleating on the RSF and reduce the crystallinity of RSF/PLA composites.3. The objective of this study was to evaluate the interfacial adhesion of the RSF/PLA composites as a proper interface compatilizer (Phthaloyl-chitosan-g-poly(lactic acid) PHCS-g-PLA) was added. The results of Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) indicated that PHCS-g-PLA was successfully synthesized. When PHCS-g-PLA added up to 7 wt%(based on composites mass), RSF/PLA composites showed maximum tensile strength which increased by 25% compared with the blank sample. The SEM and water absorption test results demonstrated that addition of PHCS-g-PLA can improve interfacial adhesion between RSF and PLA. TGA results showed that thermal stability of RSF/PLA composites was not improved with an increasing PHCS-g-PLA content. DSC data showed that the addition of PHCS-g-PLA reduced the crystallinity of RSF/PLA composites.4. The effect of RSF that was modified by suspension polymerization of butyl acrylate (BA) monomer on the interfacial adhesion of the RSF/PLA composites was studied. The modified rice straw fiber (MRSF) was characterized by FTIR and SEM, and the results indicated that poly(butyl acrylate) (PBA) was adsorbed and coated on RSF. The results of mechanical properties showed that the tensile strength of PLA/MRSF composites (W(%)=7.98) increased 25% compared with the blank sample. A morphological study of PLA/MRSF composites (W(%)=7.98) via SEM showed good interfacial adhesion between PLA and RSF and good dispersion of RSF in the polymer. The water absorption of the PLA/MRSF composites was lower than the blank sample. TGA results confirmed that thermal stability of PLA/RSF composites increased with PBA increasing. DSC data showed that PBA made crystallization of PLA more difficult and incomplete.In summary, three improving interfacial adhesion methods in this study showed their own features and can be chosen according to practical requirements. RSF filler content was 10%(based on composites mass) that proved above methods were feasible and the 30% and more RSF filler content will be added in the future. RSF/PLA composites may be used in agriculture, one-off instruments, new packaging materials and many other fields although these composites were still in stage of fundamental research at present.