【作者】 郭文静；

【导师】 鲍甫成； 王正；

【作者基本信息】 中国林业科学研究院 ， 木材科学与技术， 2008， 博士

【摘要】 以可再生的木质材料和来源于植物资源且可生物降解的聚乳酸为原料制备可生物降解木纤维/聚乳酸(WF/PLA)生物质复合材料是生物质复合材料领域中新的研究方向。WF/PLA复合材料的研究开发对于解决日益增长的环境污染危害和有限石油资源引起的能源危机具有重要意义。本论文主要研究WF/PLA复合材料的复合因子及其作用机理,为生物质复合材料的发展提供基本依据。本文就熔融挤出法、高速混合法、物理混合法三种典型复合方式、复合温度和木纤维水分对WF/PLA复合材料的物理力学性能、聚乳酸聚集态结构及热性能的影响进行了研究。在此基础上,系统研究了木纤维含量、不同改性聚乳酸及相容剂对WF/PLA复合材料结构与性能的影响机制,并对不同WF/PLA复合材料的降解特性进行了综合评价与分析。本论文的主要研究结果为:(1)复合方式对WF/PLA复合材料及其聚乳酸相的结构与性能影响显著在物理混合法、高速混合法、熔融挤出法三种复合方式中,木纤维与聚乳酸经历的热与剪切作用不同,复合方式对WF/PLA复合材料结构与性能有显著影响。不同复合方式引起聚乳酸分子降解是影响复合材料性能的关键。熔融挤出法中,原料受热时间长、剪切作用强,聚乳酸分子降解严重,重均分子量((M|-)w)和数均分子量((M|-)n)分别只有聚乳酸原料的13.5%和14.6%,聚乳酸熔点明显降低,复合材料弯曲强度最低,但密度最高、耐水性最好。物理混合法中,木纤维与聚乳酸只经简单混合,聚乳酸分子降解较少,(M|-)w和(M|-)n分别是聚乳酸原料的69.9%和67.3%,复合材料的弯曲强度最高,密度最低,但耐水性差。高速混合法中,木纤维与聚乳酸受热与剪切作用的强度与时间适中,复合材料综合性能最好,聚乳酸的(M|-)w和(M|-)n分别为聚乳酸原料的51.0%和51.9%,复合材料弯曲强度为45.12MPa,密度较低,耐水性较好,弯曲模量最高。(2)复合温度对WF/PLA复合材料结构与性能影响显著,而木纤维水分对复合材料结构与性能影响不显著在捏合熔融制备WF/PLA复合材料过程中,随着复合温度升高,聚乳酸相的(M|-)w明显下降。在复合温度180℃和190℃之间,Mn变化不显著,复合温度增加到200℃时,聚乳酸相的(M|-)n明显下降。复合温度为190℃时,聚乳酸相的熔融温度最低。(3)木纤维含量与WF/PLA复合材料的结构和性能具有明显的相关关系在WF/PLA复合材料中,随木纤维含量由30%增加到60%,复合材料的密度、弯曲模量增加,弯曲强度和耐水性下降;但是,当木纤维含量由70%增加到90%时,复合材料的密度、弯曲强度、弯曲模量及耐水性都呈下降趋势。木纤维与聚乳酸复合可以提高材料的弯曲模量。木纤维与聚乳酸复合后,聚乳酸分子降解严重。随着木纤维含量增加,聚乳酸的(M|-)w和(M|-)n明显下降,冷结晶温度、玻璃化转变温度、熔融温度和热分解温度也降低。(4)不同改性聚乳酸与相容剂制备的WF/PLA复合材料的结构与性能不同不同改性聚乳酸与木纤维复合,聚乳酸分子都发生分解,分子量明显下降。聚乳酸分子量越低,复合材料的力学强度越差,耐水性越差。添加相容剂的效果,聚决于相容剂对聚乳酸分子降解程度的影响。相容剂在WF/PLA复合材料制备中主要作用是保护聚乳酸分子在复合过程中不发生断链降解。马来酸化聚丙烯CA60可以提高WF/PLA复合材料力学强度,但聚乳酸分子降解严重,其复合材料耐水性极差;添加马来酸化聚丙烯M300或H1100P可以改善复合材料的耐水性,聚乳酸相的(M|-)w和(M|-)n较无相容剂的复合材料都明显增加。添加脂肪酸胺基相容剂AD281后,复合材料中聚乳酸的(M|-)w变化不大。丙烯酸改性聚四氟乙烯相容剂A3000可以很好地增加复合材料成分间相容性,使复合材料中聚乳酸相分子量增加。AD281和A3000对于提高复合材料耐水性有显著作用。(5)WF/PLA复合材料具有很好的降解特性不同配方的WF/PLA复合材料陈放24个月后,弯曲强度值保留率基本在75%以上,弯曲模量值都高于5000MPa,保留率在85%以上。WF/PLA复合材料具有一定的耐久性。WF/PLA复合材料适用于使用周期相对较短,而对材料废弃后降解有要求的应用领域。WF/PLA复合材料发生降解的重要标志就是聚乳酸分子的降解。经土埋6个月降解后,不同配方的WF/PLA复合材料,降解程度各不同。与纯聚乳酸相比,WF/PLA002、WF/PLA022和WF/PLA/AD281复合材料中聚乳酸的(M|-)n和(M|-)w降幅更大,复合材料中的改性剂或相容剂未发生改变。WF/PLA012、WF/PLA003、WF/PLA002/A3000经降解实验后,聚乳酸相分子量没有下降,而且改性剂或添加剂的分子量特征峰改变或消失。WF/PLA复合材料的力学强度、非晶区与结晶区特征都表明WF/PLA复合材料经土埋后发生了明显的降解。木纤维/聚乳酸复合材料中聚乳酸比纯聚乳酸塑料更容易降解,更具有环境友好性。总之,复合方式、复合温度、木纤维含量、聚乳酸特性对木纤维/聚乳酸复合材料材料的结构与性能都有显著影响。WF/PLA复合材料的物理力学性能、热性能与复合材料中聚乳酸的分子量有明显的相关关系。木纤维与聚乳酸复合后,促进了聚乳酸的降解,是真正的环境友好的生物质复合材料。更多还原

【Abstract】 Wood fiber/poly(lactic acid) (WF/PLA) bio-composite based on renewable wood material and biodegradable poly(lactic acid) made from corn starch is a fully biodegradable and environmental friendly bio-composite and it is one of the important research area of bio-composites. The WF/PLA bio-composites would be of great importance to the material world, not only as a solution to growing environmental threat but also as a solution to the uncertainty of petroleum supply. The compounding factors and mechanisms influencing the structures and properties of the WF/PLA bio-composites were analyzed in this thesis. It was hoped to provide the basal data for the development of WF/PLA bio-composites.The effects of three representative compounding mode, including extrusion, high-speed mixing and physical mixing, compounding temperatures and the moisture content of wood fiber on aggregated state structure, physical-mechanical and thermal properties of the WF/PLA composites were studied. Then the influencing mechanisms of wood fiber content, modified poly(lactic acid) and compatilizers on the structures and properties of the WF/PLA composites were analyzed systemically. The property endurance and the degradation of the WF/PLA composites were investigated and evaluated too.The main results are as follows:(1) The influences of compounding modes on the structures and properties of WF/PLA composites were significant.The wood fiber and poly(lactic acid) in the WF/PLA composites experienced different thermal and shear stress reactions during compounding. The influences of compounding modes on the structures and properties of WF/PLA composites were significant. The poly(lactic acid) degraded arose from different compounding modes was the key that affected the properties of WF/PLA composites.In extrusion mode, components experienced a long thermal history and stronger shearing stress. The poly(lactic acid) molecular in WF/PLA composites degraded seriously and the weight-average molecular weight ((M|-)w) and number-average molecular weight ((M|-)n) of the poly(lactic acid) in the WF/PLA bio-composites were just 13.5% and 14.6% of that of the raw material. The melt temperature decreased significantly and the flexural strength of the WF/PLA composites were the lowest. But the density and water resistance of the WF/PLA composite were the highest and the best each, because the poly(lactic acid) and wood fiber compounded thoroughly. In the physical mixing mode, wood fiber and poly(lactic acid) were just mixed physically and the poly(lactic acid) in WF/PLA composites degraded lesser. The (M|-)w and (M|-)n of poly(lactic acid) reserved 69.9% and 67.3% of that of raw poly(lactic acid). The flexural strength of the composites is highest, but the density was the lowest and water resistance was the poorest. In high-speed mixing, the thermal and shearing stress were moderate. WF/PLA composites made by high-speed mixing mode got preferable general properties. The (M|-)w and (M|-)n of poly(lactic acid) in WF/PLA composites were 51.0% and 51.9% of the raw poly(lactic acid). The flexural strength of the composite was 45.12MPa. Low density, better water resistance and highest flexural modulus were got for the WF/PLA composites by high-speed mixing mode.(2) The effects of compounding temperatures on the structures and properties of WF/PLA composites were significant, but the effects of wood fiber moisture contents were not significantDuring the preparing of WF/PLA composites by kneading, the (M|-)w of poly(lactic acid) in WF/PLA composites decreased significantly when the compounding temperature increaed from 180℃to 200℃. The (M|-)n changed a little between 180℃and 190℃, but it decreased significantly when the compounding temperature increased from 190℃to 200℃. At compounding temperature 190℃, the melt temperature of the poly(lactic acid) was the lowest.(3) The correlativity between wood fiber content and the structures and properties of WF/PLA composites was obviousWith the wood fiber content increased from 30% to 60%, the density and flexural modulus of the composites increased, but flexural strength and water resistance decreased. When the wood fiber content increased from 70% to 90%, the density, flexural strength, flexural modulus, and water resistance all decreased. The flexural modulus of the composites were increased by compounding wood fiber with poly(lactic acid).The molecular weight decreased seriously when wood fiber compounded with poly(lactic acid). With the wood fiber content increased, the (M|-)w and (M|-)n of poly(lactic acid) decreased obviously, and all the cold crystal temperature, glass transition temperature, melting temperature and decomposition temperature decreased.(4) The structures and properties of WF/PLA composites made of different modified poly(lactic acid) and compatilizers were different.The poly(lactic acid) degraded and the molecular decreased significantly when different modified poly(lactic acid) compounded with wood fiber. The smaller the poly(lactic acid)’s molecular was, the lower the mechanical strength and the poorer of water resistance of the composites were.The effects of adding compatilizers on the properties of the WF/PLA composites were determined by the degraded extent of poly(lactic acid) caused by the compatilizers. The important role of the compatilizers in WF/PLA composites were to protect the poly(lactic acid ) molecular not to degrade during compounded.Compatilizer maleic polypropylene CA60 increased the flexural strength of the composites, but led the poly(lactic acid) of the composites degraded seriously, and the water resistance of the composites was the poorest. The (M|-)w and (M|-)n of poly(lactic acid) in composites with compatilizer maleic polypropylene M300 or H1100P were not increased significantly compared with the composites without compatilizer. They could improve the water resistance of the WF/PLA composites obviously. The (M|-)w of WF/PLA composites with compatilizer fatty acid amide AD281 was similar to that of without compatilizer. Polyterrafluoroethylene coated with acrylate polymer A3000 could improve the compatibility of the components, and increase molecular weight of poly(lactic acid) in composites. The result of AD281 and A3000 to improve the water resistance of the composites were obvious.(5) The biodegradability of WF/PLA composites was excellentAfter placed in room for 24 months, the WF/PLA composites still preserved 75% flexural strength and 85% flexural modulus compared to original mechanical properties. The results indicated that the endurance of WF/PLA composites can meet the need of use. The biodegradable WF/PLA composites are much more suitable used in the case of short term and requirement of biodegradation properties for the products.For the WF/PLA composites with different formulations, molecular degradation of poly(lactic acid)was the important character of the composites degraded. After buried in soil for 6 months, the biodegradation of WF/PLA composites was different. (M|-)w and (M|-)n of the composites WF/PLA002, WF/PLA022, WF/PLA/AD281 were decreased much more after buried in soil for 6 months. At the same time, there weren’t changes for the modifier and compatilizer in the composites. For WF/PLA012, WF/PLA003 and WF/PLA002/A3000 composites, the molecular weight of poly(lactic acid) in composites did not decreased, and the molecular curves of modifiers or compatilizers changed or disappeared.The flexural strength and flexural modulus of the WF/PLA composites, crystal and non-crystal areas of poly(lactic acid) all indicated that the composites degraded obviously after buried in soil for 6 months. The poly(lactic acid) in WF/PLA composites were easily degraded than raw (lactic acid) itself.In conclusion, the effects of compounding mode, temperature, wood fiber content and different poly(lactic acid) on the structure and properties of the WF/PLA composites were significant. The correlativity between the thermal, physical-mechanical properties and the molecular weight of poly(lactic acid) of the composites is very obvious too. The degradation of poly(lactic acid) was promoted when it was compounded with wood fiber. But the property endurance and the degradation properties of WF/PLA composites were excellent. WF/PLA composites are the environmental friendly bio-composites.更多还原