| Summary: | 碩士 === 國立嘉義大學 === 食品科學系研究所 === 106 === In the first part of this study, hot pressed (150°C and 20-25 kgw/cm2) composite boards were made of SCB and CA at concentration of 0, 5, 10, 15, and 20 wt% SCB (denoted as SCB-CA 0, SCB-CA 5, SCB-CA 10, SCB-CA 15 and SCB-CA 20, respectively). Physiochemical properties of boards were analyzed. The results showed that the boards prepared under these conditions were molded without any delamination. Different amounts of citric acid didn't cause significant differences in dimension of the boards. As for general appearance and color attributes, the boards gradually changed from yellow-brown to dark-brown with the increase of citric acid content. While the mechanical properties increased as the CA amount increased, the maximal values were detected in SCB-CA 15 board. Since these maximal mechanical properties were higher than those of polystyrene boards, it is indicated that CA exhibited good adhesive property in board making process. The SCB-CA 15 and the SCB-CA 20 exhibited better water resistance, indicating that the addition of citric acid rendered the boards with good dimensional stability. FTIR analysis confirmed that citric acid cross-linked with SCB fibers under hot-pressing conditions. The carboxyl groups in the CA reacted with hydroxyl groups in the fibers to form hydrophobic ester bonds. The cross-linking reaction increased mechanical properties and improved dimensional stability. Citric acid can be considered as a good natural adhesive for SCB composite boards. Based on the results of part one, 15 wt% and 20 wt% were regarded as the preferred amount of citric acid for composite boards. In the second part, the effects of surface modification technology on physicochemical properties of SCB composite boards were investigated.
In the second part of this study, Pleurotus ostreatus was inoculated on SCB for solid-state fermentation to produce laccase. Laccase mediator system (LMS) composed of laccase and syringaldehyde was used to modify the surface of SCB fibers and the phenolic hydroxyl content of the SCB surface was analyzed. The results showed that the SCB fibers treated with LMS for 1 h exhibited the lowest free radical scavenging activity by 21.32±0.90%. More rough fiber surface of SCB after enzyme treatment was observed in the surface microstructure, which might facilitate the penetration of CA adhesive. FTIR analysis showed that grafting reaction occurred on the modified surface of SCB and more ester bonds were formed in the boards. Compared to the first part, the enzyme-modified boards had better color appearance, mechanical properties and dimensional stability than SCB composite boards without surface modification.
In conclusion, the combination of using citric acid as natural adhesive and surface modification with laccase and syringaldehyde could successfully manufacture novel green composite materials.
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