增容剂改善茶粉/聚乳酸生物质复合材料性能

为降低聚乳酸的生产成本、拓宽其应用范围和高值化利用茶产业剩余物资源,以茶粉(tea dust,TD)为填料,聚乳酸(polylactic acid,PLA)为基体,经密炼、注塑工艺制备了环境友好型TD/PLA复合材料。以过氧化二异丙苯(dicumyl peroxide,DCP)为引发剂,通过熔融反应制备了甲基丙烯酸缩水甘油酯接枝聚乳酸(glycidyl methacrylate grafting PLA,GMA-g-PLA),用傅里叶红外光谱(Fourier transform infrared spectrum,FTIR)和核磁共振氢谱(H nuclear magnetic resonance,1H-NMR)对其进行了表征,并以GMA-g-PLA为增容剂,考察了其添加对TD/PLA复合材料力学性能、界面形态、热性能及吸水性能的影响。结果表明,FTIR和1H-NMR分析证实了GMA成功地接枝到了PLA上。GMA-g-PLA的添加明显改善了TD与PLA的界面相容性,提高了TD/PLA复合材料的力学性能和热稳定性,降低了吸水率。在GMA-g-PLA添加质量分数为10%时,复合材料的力学性能最佳,与未增容TD/PLA复合材料相比,其拉伸强度、弯曲强度及缺口冲击强度分别提高43.8%、42.1%和24.1%,拉伸模量和弯曲模量提高26.5%和10.4%,断裂伸长率提高26.1%。该研究结果可为进一步探索茶塑复合材料界面改性规律及制备聚乳酸基复合材料,提供试验数据和参考。

Compatibilizer improving properties of tea dust/polylactic acid biomass composites

Abstract: With the increasing scarcity of oil resources and the aggravation of white pollution, environmentally friendly biodegradable materials have become a topic of great interest in research and development. Among the biodegradable polymers, polylactic acid (PLA) is one of the most studied and promising aliphatic polyesters derived from starch by microbial fermentation, which offers excellent properties such as high strength, good transparency and biodegradability. However, PLA also has disadvantages of poor toughness and high cost. PLA is often reinforced with natural fibers like wood flour, bamboo flour, sisal, coir and hemp to reduce the production cost. Among the various natural fibers, tea fiber is cheap and widely available especially in China. The worldwide consumption of tea is about 4.5 million tons annually, and it always ends up with lots of waste tea leaves, stalks and dusts during the process of tea production and consumption. The tea residue to use as organic filler in polymer composites shows a great prospect because of its lignocelluloses behaviors and low cost. To our knowledge, there have been few researches about the biodegradable composites by using waste tea residue as organic filler so far. However, the moisture absorption tendency and poor interfacial bonding properties of the fibers are the main drawbacks of PLA/natural fiber biomass composites. Many researches focused on surface modification of natural fibers through different methods such as mercerization, silane treatment and isocyanate treatment to improve the compatibility between natural fiber and PLA matrix. Melting grafting copolymerization is a novel modification technology for plastics, the use of PLA grafted with glycidyl methacrylate (GMA) is a relatively efficient strategy to improve both the interface adhesion and toughness of natural fiber/PLA biomass composites. In order to decrease the cost of PLA, and expand its applicability, and also to make full use of the waste tea residue, tea dust (TD) was blended with PLA to prepare environmental friendly TD/PLA composites by injection molding. PLA grafted with glycidyl methacrylate (GMA-g-PLA) was synthesized by melt grafting PLA with GMA using dicumyl peroxide as initiator, the graft copolymer was confirmed by FTIR (Fourier transform infrared spectrum) and 1H-NMR (H nuclear magnetic resonance), and the influences of GMA-g-PLA addition on the mechanical, thermal and moisture resistance properties of TD/PLA composite were investigated. GMA grafting onto PLA was confirmed by FTIR and11H-NMR spectroscopic technology. The phase morphology, thermal stability, moisture resistance and mechanical properties of TD/PLA composites compatibilized with GMA-g-PLA were improved compared with those of the composites without adding compatibilizer, as characterized by scanning electron microscopy, thermogravimetric analysis, water adsorption test and using a universal materials tester, respectively. The GMA was successfully grafted onto PLA, which was confirmed by the FTIR and 1H-NMR technology, and the grafted GMA content was 4.88% calculated by 1H-NMR analysis. The addition of GMA-g-PLA in the biocomposites obviously improved the mechanical, thermal and water adsorption properties of TD/PLA composites, which is attributed to the greater compatibility between TD and PLA matrix. The TD/PLA biomass composite with 10% (mass fraction) GMA-g-PLA showed the optimum mechanical properties, with an improvement of 43.8% in tensile strength, 42.1% in flexural strength, 24.1% in notched impact strength, 26.5% in tensile modulus, 10.4% in flexural modulus and 26.1% in elongation at break, respectively.