木质纤维-聚烯烃/实木多元复合机理

Wood-plastic composite (WPC) fabricated with lignocellulosic fibers and thermoplastics, will undergo creep deformation when it is subjected to long-term external forces. This is due to the stress relaxation of macromolecular chains ascribed to their thermodynamic movement. Meanwhile, the presence of a large amount of lignocellulosic fibers restrains the movement of the macromolecular chains. WPC will exhibit brittle fracture when suffering from an external surge. The coexistence of creep and brittle fracture is the fatal defect of WPC, which restricts its popularization and application. This is an international problem needed to be attacked in both industry and academia. However, the fast-growing solid wood with good rigidity and toughness as the core material, the waterproof WPC as the protective shell layer, which can fabricate multi-phase composites using multi-phase co-extrusion technology. This innovative technology can greatly improve the creep and brittle fracture resistance of the resulting composites simultaneously. It is not yet mature due to lack of theoretical support. Herein, this project will exploit the co-extrusion technology to produce lignocellulosic fiber-polyolefin/solid wood multi-phase composites (WPC-W). A systematic study will be conducted focusing on the interfacial adhesion between WPC and wood, the melt rheology, the creep and brittle fracture mechanisms of WPC-W, and the relationship between cross-sectional structure of WPC-W and creep/brittle fracture behavior. The key point is to reveal the composite mechanisms of WPC-W, providing theoretical support for manufacturing technology of WPC-W.

以木质纤维与热塑性聚合物为主要原料制备的木塑复合材料，当长期受到重力等外力缓慢作用时，聚合物链热运动克服分子间作用力使材料产生应力松弛而表现为蠕变；同时，大量木质纤维的存在约束了聚合物链的运动，当受到外力冲击的瞬间作用时应力集中而使材料表现为脆断。蠕变与脆断并存是木塑性能的两个致命缺点，制约其在更广泛领域的推广应用，为产业界和学术界关注的国际难题。课题组提出以刚性好韧性强的速生实木为芯层、以防水防潮的木塑为表层，复合制备木塑/实木多元复合材料的新思路，初步获得抗蠕变和抗脆断性能均大幅提高的技术效果，但因缺乏理论支撑而尚未成熟。本项目采用共挤法制备木质纤维-聚烯烃/实木多元复合材料，以木塑/实木界面结合、熔体流变、多元复合材料的蠕变脆断机理及其与复合材料截面结构关系为重点，开展系统研究，揭示木质纤维-聚烯烃/实木多元复合材料的复合机理，为建立木塑/实木多元复合材料制造技术提供理论基础。

蠕变与脆断并存是木塑复合材料（木塑）性能的两个致命缺点，严重制约了木塑在高档门窗、交通工具、绿色建筑、海洋工程等高附加值领域的大规模推广应用，为产业界和学术界关注的国际难题。本项目采用共挤出成型方法制备了木质纤维-聚烯烃/木竹多元复合材料，通过对木塑/木竹界面结合、熔体流变、多元复合材料蠕变、脆断行为、复合材料截面结构性能关系的系统研究，揭示了木质纤维-聚烯烃/木竹多元复合材料的复合机理、抗蠕变和抗脆断机理。针对多功能壳层、高性能木塑和竹木复合材料结构材的不同特点，通过多元级配设计，扬长避短、优势互补，利用多功能壳层的保护阻隔和韧性、高性能木塑的高硬度和高抗压性，高强重比竹/木复合结构材的强韧和抗蠕变性，采用具有自主知识产权的共挤成型技术与装备，创制了轻质高强高韧抗蠕变的多功能木塑/竹-木多元复合结构材。基于木塑溶体流变学研究、挤出流场数值模拟和多尺度界面机理研究，设计发明了高界面结合强度的共挤出专用模具，解决了聚烯烃木塑层与木竹材界面结合差的技术难题，建立了轻质高强耐候木塑/竹-木多元复合共挤制造技术，突破了木塑复合材料易蠕变、易脆断的国际技术瓶颈。典型产品的密度0.73g/cm3、弯曲强度87.6MPa、弹性模量8.2GPa、冲击强度66.8kJ/m2、蠕变恢复率94%、抗滑值69.6、冷热循环试验长度尺寸变化率0.02%、UV加速老化试验静曲强度保留率高达96.8%。为推动木塑复合材料在对承重、耐候、抗蠕变等性能要求更高领域的应用，具有重要意义。