【作者】 黄润州；

【导师】 张洋； 吴清林；

【作者基本信息】 南京林业大学 ， 木材科学与技术， 2012， 博士

【摘要】 本研究以新型的芯-表结构的木塑复合材料和传统的木(竹)塑复合材料为研究对象,以HDPE为基体,有机填料与无机填料混合使用探讨了(1)芯-表结构木塑复合材料的表层性能对复合材料整体性能的影响,以机械力学性能为基础,分析了其热膨胀性能并建立了芯-表结构木塑复合材料的有限元模型；(2)以机械性能为基础,研究了传统木(竹)塑复合材料的热膨胀性能。本研究得到的结论归纳如下：(1)当单一填料(滑石粉(Talc)或玻璃纤维(GF))作为增强材料增强芯-表结构木塑复合材料表层时,GF对其表层材料的拉伸模量的提高效果更明显,将已有的模型预测值与测量值进行了比较,PPA可以预测HDPE/GF复合材料的拉伸强度和模量及HDPE/GF复合材料的拉伸模量；Nicolais和Nicodemo建立的模型可用于预测HDPE/Talc复合材料的拉伸强度；HDPE/GF表层材料的弯曲强度和模量更大,其冲击强度随着纤维加入量的增加而提高；DMA测试结果与弯曲性能测试结果相似,与纯HDPE相比,HDPE/GF表层材料的α松弛峰通常出现在较高的温度区域,而HDPE/Talc表层材料出现α松弛峰的温度区域与纯HDPE相近；HDPE/GF表层材料的Tan8值随着GF加入逐渐降,HDPE/Talctanδ值未发生明显变化。当混合填料(Talc和GF)按l0wt%和30wt%增强材料增强芯-表结构木塑复合材料表层时,无论混合填料的比例(Talc:GF)是1：1,1：2或者是1：3,复合材料的力学性能都有提高。混合填料中GF的含量越高,其复合材料的力学性能越好,当填料加入量为30wt%时,表现的尤为明显。DMA分析与弯曲性能的测试结果相一致。E′随着填料含量的增加而升高,E＂『在50℃--62℃左右出现α松弛内耗峰。总的来说,Tan8值随着填料含量的增加而降低。无论填料是单一还是混合加入,随着温度的升高(降低),其复合材料的尺寸变化不断变大(变小)。填料的加入降低了其复合材料的热膨胀,纯HDPE(AD60)试样具有较明显的残留变形；当GF在HDPE/GF复合材料中含量较高(30%和40%).时,其复合材料的残留变形较小；HDPE/Talc复合材料的残留变形与纯HDPE相似；HDPE/GF复合材料与同样木粉含量的WPC相比,具有较小的LTEC;混合填料中GF/Talc比例以1：1增强表层时,表层的LTEC值最小。(2)对于纤维状的GF增强表层的芯-表结构木塑复合材料而言,当表层的弯曲模量小于芯层的弯曲模量时,随着表层厚度的增加,芯-表结构木塑复合材料的弯曲模量逐渐下降；当表层的弯曲模量高于芯层的弯曲模量时,则复合材料弯曲模量随表层厚度的变化趋势恰恰相反,复合材料弯曲模量随表层厚度的增加而增加。由芯-表结构木塑复合材料(GF增强表层)表层及芯层随温度变化的应变分布的有限元分析可知,模型中左端点随着温度的升高而限制膨胀(-0.007027),材料的热变形从左至右呈现线性增长,右侧有较大的热变形；芯-表结构木塑复合材料的LTEC随表层厚度的变化趋势较为复杂,它是表层和芯层性能共同作用的结果。LTEC随表层的厚度呈现线性变化。当表层的LTEC值大于芯层LTEC时,表层厚度的增加可以导致芯-表结构木塑复合材料LTEC的增加；当表层的LTEC值小于芯层LTEC时,芯-表结构木塑复合材料LTEC随表层厚度的增加而减少；总的来说,芯-表结构木塑复合材料(GF增强表层)的热膨胀系数的测量值和有限元模型模拟值是契合的,芯-表结构木塑复合材料复合材料(Talc增强表层)的弯曲性能随着表层滑石粉加入量的增加而增加,即随着表层弯曲性能的增加而增加；降低复合材料表层材料的热膨胀系数的同时可以一起降低芯-表结构复合材料的热膨胀系数；当表层厚度降低为芯层的一半时,由于Talc是片状结构,故表层材料的滑石粉的含量从0依次增加到10wt%时,芯-表结构木塑复合材料热膨胀系数显著降低,而当表层滑石粉从10wt%依次增加到49wt%时,其热膨胀系数降低的不显著。(3)纯R-PP&PE的热膨胀残留变形较大,而添加了单一或混合填料的复合材料的热膨胀残留变形明显较小；当PCC加入量从3wt%增加到30wt%时,随着PCC含量的升高复合材料的LTEC显著降低。较纯的R-PP&PE基体,PCC加入量为0时,当40wt%GBP(TGBP)或者RBF(TRBF)加入塑料基体后,其复合材料的LTEC在3个温度区间内均下降；PCC加入后,复合材料的LTEC随着PCC含量的增加而减小；当PCC的加入量相同时,经硅烷处理过的有机填料具有更好的降低热膨胀的效果；TRBF较TGBP也具有更好降低复合材料热膨胀的效果。(4)随着WPC的木粉含量从0增加到35%,其弯曲强度和弯曲模量不断增强,其线性热膨胀系数呈下降的趋势,且对长度方向上的热膨胀的限制较宽度方向上更大；在加入木粉未加入偶然联剂的情况下,木塑复合材料的冲击强度呈现下降趋势,加入偶联剂后的木塑复合材料的热膨胀系数较未加入任何类型的偶联剂的木塑复合材料热膨胀系数均有显著降低,其拉伸模量和冲击强度均有所提高,木粉与偶联剂的加入均对WPC的热膨胀有限制作用,但主要的影响因素应该是木粉的加入量及塑料基体的种类；当单一的PA或者SEBS加入后,HDPE/PA(SEBS)复合材料的LTEC呈下降趋势,但幅度不大,SEBS-G-MA加入后,复合材料继续呈现下降趋势,当竹粉加入后,复合材料的LTEC显著下降,当竹粉,PA,SEBS-G-MA和MAPE(PEAC4)共同作用时候,复合材料的热膨胀系数最低,影响复合材料LTEC最主要的因素是竹粉的加入量。更多还原

【Abstract】 Mechanical/thermal expansion coefficients of co-extruded wood plastic composite(core-shell) or WPC were investigated in this paper. The filler involved talc,glass fiber, PrecipitatedCaCO3, pine fiber, bamboo flour. The effect of individual and combined filler on mechanical and thermal performance of the filled HDPE composites was studied to develop a suitable shell system for co-extruded wood plastic composites (core-shell) and mechanical/thermal expansion behavior of WPC. The model provides a way to optimize raw material composition for minimize thermal expansion behavior of co-extruded WPC(core-shell).The following conclusions can be drawn from the study.(1) The use of silane-modified short GFs had a much larger effect in improving mechanical properties and in reducing LCTE values of filled composites compared with the use of un-modified talc particles due to enhanced bonding to the matrix, larger aspect ratio and fiber alignment for GFs. Mechanical properties and LCTE values of composites with combined talc and GF fillers varied with talc and GF ratio at a given total filler loading level. The use of a larger portion of GFs in the mix can lead to better composite performance, while the use of talc can help lower the composite costs and increase its recyclability. The use of30wt%combined filler seems necessary to control LCTE values of filled HDPE in the data value range generally reported for commercial wood plastic composites. Tensile modulus for talc-filled composite can be predicted with role of mixture, while a PPA-based model can be used to predict the modulus and strength of SGF-filled composites.(2)Coextruded wood plastic composite(core-shell) with glass-fiber (GF) filled shells were manufactured and their mechanical/thermal expansion coefficients were evaluated. The use of GF-filled shell enhanced overall composite modulus and strength, and at the same time, lowered composite linear coefficient of thermal expansion (LCTE). The imbalance of shell and core LCTE and moduli led to complex stress field within the composite system. Three-dimensional finite element model based on linear isotropic material for both shell and core was developed to predict LCTE of the material. The model predicted a trend which is in general agreement with the experimental data. The model provides a way to optimize raw material composition for minimize thermal expansion of WPC. For coextruded wood plastic composite(core-shell)with talc filled shell system, flexural properties of composite increased with the increase of talc content. LTEC of the co-extruded wood plastic composite decreased with decrease of the LTEC for the shell. (3) Thermal expansion of the composites decreased with increased PCC and bamboo filler loading levels. The composite system with RBFs had smaller LCTE values than those from systems with GBPs. The use of silane treatment on bamboo fiber/particle surface helped with their bonding to the plastic matrix, leading to further reduction of LCTE values for both GBP and RBF systems. The observed behavior of reduced LCTE is attributed to a small filler LCTE value, reduced over-plastic volume, and enhanced interfacial bonding with treated materials. Thus, hybrid bamboo and PCC fillers are suitable materials for controlling the thermal expansion of the composite materials caused by temperature changes.(4) The flexural and thermal expansion properties of composites was investigated. The flexural strength and modulus of composites was higher than that of pure PE, which were increased with increasing fiber content. As the filler loading increased, the thermal expansion of composites slightly decreased, The modifier content showed better influences on the longitudinal LTEC than that of tangential; Without addition of modifiers, tensile strength of composites was lower than virgin HDPE. Tensile modulus is not sensitive to content of coupling agent.LTEC change of various composites was primarily caused by the matrix and filler content; Low impact strength is the major drawback of WPC in many end-use applications. The impact strength’change of composites is caused by coupling agents. The different matrix and ratio of modifier content showed different influences on the various Linear thermal expansion coefficients of composites in three temperature zone, the reduction of the LTEC appear in HDPE/Pine composites was not dependent on coupling agent. Therefore, LTEC change of various composites was primarily caused by the matrix and filler. When the PA, SEBS of bamboo flour filled to the matrix, the LTEC was reduced.SEBS-G-MA as couple agent can reduced the LTEC of the BF/PA/HDPE composite, but LTEC of composites was primarily caused by the bamboo flour更多还原