【作者】 周吓星；

【导师】 林巧佳； 陈礼辉；

【作者基本信息】 福建农林大学 ， 木材科学与技术， 2012， 博士

【摘要】 木塑发泡复合材料可以克服木塑复合材料密度大、成本高、韧性低等缺陷，而且具有比强度高、加工性能好、价格低廉等优点；在室内装潢、建筑装饰、包装运输、汽车制造业等领域存在广阔的发展前景。论文以竹粉为增强相，以聚丙烯（PP）和高熔体强度聚丙烯（HMSPP）共混塑料为基体、以自制改性AC为发泡剂，注塑法研发竹粉增强聚丙烯发泡复合材料。论文研究了PP/HMSPP不同配比对竹粉/PP发泡复合材料力学性能的影响，筛选出PP与HMSPP配比为80︰20的共混塑料基体。通过热重-差热分析，筛选出适合的发泡剂类型；并对AC发泡剂进行改性，比较了热平衡型及改性AC发泡剂对发泡复合材料力学性能、泡孔形态、加工性能和热稳定性的影响。采用1%改性AC发泡剂时，发泡复合材料的力学性能最佳，泡孔直径较小、泡孔形态分布较为均匀；加工性能和流变性能增强，发泡复合材料的表观黏度对剪切速率的依赖性变小，但粘温依赖性增大，粘流活化能为46.42KJ/mol，提高了8.9%；对发泡复合材料的热稳定性有一定不良影响。论文研究了MAPP、KH570、TL-4和DN301四种偶联剂对竹粉/PP发泡复合材料力学性能、吸水性能、表面润湿性、加工性能和流变性能以及热稳定性能的影响。经偶联剂改性后，发泡复合材料的吸水性能和表面润湿性均得到改善。当MAPP用量为9%时，发泡复合材料的综合性能最佳，比弯曲、比拉伸和比冲击强度分别提高了23.1%，9.9%和47.8%；熔体指数MI由未改性时的2.79g·10min^-1增大至3.61g·10min^-1；但热稳定性略微下降。其次是KH570，其最佳用量为2%；此时，发泡复合材料的强度分别提高了7.1%、5.8%和24.9%；MI降至2.55g·10min^-1；且热稳定性下降。再次是TL-4，其最佳用量为1%，发泡复合材料的比强度分别提高了11.7%、10.5%和16.9%；MI增至4.50g·10min^-1。最后是DN301，其最佳用量为2%，比强度分别提高了9.6%、6.8%和11.8%；MI增至3.97g·10min^-1；热稳定性略微增强。本文研究了偶联剂类型及用量对竹粉/PP发泡复合材料动态流变性能的影响。通过计算低频区lgG′-lgf曲线的斜率，衡量改性前后发泡复合材料的均相性；采用Cross方程拟合复合材料黏度和频率之间的关系，利用频率水平平移因子α（wt%），实现不同固体粒子填充材料之间线性粘弹性的转换；结合Han曲线、Cole-Cole图侧面反应了改性前后发泡复合材料内部结构、松弛过程的变化；通过幂律方程计算非牛顿指数，探讨了偶联剂对发泡复合材料流体行为的影响。竹粉/PP发泡复合材料的模量和复数黏度随着偶联剂用量的增加均呈现先降低后增大的趋势，且总体下降；且均相性提高。9%MAPP、2%KH570、1%TL-4和2%DN301改性发泡复合材料的低频区lgG′-lgf曲线的斜率由未改性时的0.709分别增至0.782、0.758、0.842和0.811。添加偶联剂不会改变竹粉/PP发泡复合材料的非牛顿假塑性流体特征，随着MAPP用量的增加，发泡复合材料的牛顿性增强；随着KH570用量的增加，发泡复合材料的假塑性增强；随着TL-4用量的增加，发泡复合材料的非牛顿指数先增大后减小；而DN301对发泡复合材料非牛顿指数的影响很小。采用环境扫描电镜观察改性前后竹粉/PP发泡复合材料的断面形态；用傅里叶红外光谱分析改性前后竹粉的基团变化；用X-射线光谱分析改性前后发泡复合材料表面的元素和基团变化，用X-射线衍射分析改性前后发泡复合材料晶体形态和结晶度变化，较为深入地研究了界面改性及其化学键结合机理。MAPP中的马来酸酐可与竹粉中的羟基发生酯化反应；从而改善竹粉和PP的界面结合力；硅醇与竹粉在加热过程中可形成-Si-O-C键；TL-4可与竹粉反应引入羧基等有机官能团；从而对竹粉表面起到“修饰”作用。偶联剂不会影响基体的晶态结构，均为α-晶形PP；但发泡复合材料的结晶度增大，未改性时发泡复合材料的结晶度为21.05%；经MAPP改性，结晶度增至31.52%。论文采用单因素实验，优化注塑工艺为：注塑温度175℃^-190℃、模具温度90℃；注塑压力4.5MPa-6.5MPa；注射速度40mm/s-70mm/s。同时，竹粉用量为50份时，发泡复合材料的综合性能最佳。采用9%MAPP、1%改性AC发泡剂、竹粉用量为50份时，发泡复合材料的平均泡孔直径为81.3μm，泡孔密度为2.66×107个/cm3；接近微孔发泡的要求；发泡复合材料的密度为0.845g·cm-3、弯曲模量为2813.31MPa、比弯曲强度、比拉伸强度和比冲击强度分别为47.59MPa、26.12MPa和7.22KJ·m-2；与未发泡复合材料相比，密度下降了16.1%、比强度提高了16.8%-40.2%，且耐热性能也略微提高。同时，建立了表征材料表面动态润湿性的数学模型，采用系数K评价了竹粉用量和偶联剂对发泡复合材料表面润湿性的影响，当竹粉用量为50份、添加9%MAPP时，蒸馏水和甘油中的初始接触角分别为88.5°和91.5°，接触角衰减速率K值分别为0.0071和0.0119，表面自由能为34.19mJ·m-2。论文采用旋转流变仪，研究了竹粉用量对竹粉/PP发泡复合材料流变性能的影响。发泡复合材料在低频区出现“似固体行为”；储能模量、损耗模量和复数黏度随着竹粉用量的增加逐渐增大；竹粉用量为10份和30份时，损耗角正切值tanδ略微增加，而随着竹粉用量的继续增加，tanδ不断降低。发泡复合材料的零剪切黏度随着竹粉用量增加不断增大，Cross特征松弛时间λ也逐渐增大，而Cross速率常数和非牛顿指数基本呈减少趋势。论文研究了滑石粉、聚烯烃弹性体POE和POE-g-MAH三种增韧填料对发泡复合材料力学性能、加工性能、流变性能和热稳定性能的影响。当竹粉用量为50份、MAPP为9%、改性AC为1%时，添加8%POE-g-MAH增韧的竹粉/PP发泡复合材料的综合性能最佳，其力学性能可满足代替PP塑料应用于汽车内饰件的要求。此时，发泡复合材料的密度为0.849g·cm-3，比弯曲强度为45.72MPa、弯曲模量为3019.91MPa、比拉伸强度为25.22MPa、比缺口冲击强度为10.07KJ m-2、维卡软化点温度为155.8℃；MI为3.69g·10min^-1，能较好地注塑成型；且对发泡复合材料热稳定性基本没有影响；但表观黏度对剪切速率较为敏感。论文比较了人工加速老化和自然气候老化对添加及未添加老化剂的竹粉/PP发泡复合材料材色、尺寸、质量、弯曲性能、拉伸性能、冲击强度以及蠕变性能的影响，分别采用四元件和六元件模型模拟发泡复合材料在25%、50%和75%应力水平下的短期蠕变行为。通过添加抗氧化剂B225和抗紫外线剂UV770，可以改善发泡复合材料的耐老化性能；但是，加速老化和自然老化2160h后，其产生的色差仍分别为47和2.8，冲击强度分别下降25.3%和9.2%，拉伸强度略微增强了1.3%和6.0%；加速老化导致弯曲性能下降13%，自然老化对弯曲性能影响不大；历时5400s蠕变试验后，产生蠕变应变增大了约1.2倍；剩余抗弯性能保留率分别为91.97%-97.70%和92.66%-98.87%。更多还原

【Abstract】 Foamed natural and wood fiber-plastic composite （WPC） with a fine cellular structurecan overcome some shortcomings such as high density and low toughness of non-foamedWPC and can achieve outstanding cost-to-performance ratio and has a favorablestrength-to-weight ratio compared to its non-foamed analogue. Due to these unique properties,foamed WPC has widely used in building materials, decoration, packaging, especially in theconstruction and automotive industries and etc. In this paper bamboo powder reinforcedpolypropylene （PP） foaming composites were developed with bamboo powder asreinforcement, PP and high melt strength polypropylene （HMSPP） blends as matrix, modifiedazodicarbonamide （AC） as foaming agent and the composites were prepared by injectionmoulding.In the first interest for this study, effects of different proportions of PP and HMSPP onthe physico-mechanical properties of foaming composites were investigated and theappropriate ratio of PP and HMSPP was fixed to80︰20. Thermo-decomposition behaviorsof three types of chemical foaming agents （CFA） such as endotherimic, exo-endothermic andexothermic CFA were carried out and the suitable type of CFA was selected. Then, effects ofexo-endothermic FA and modified AC （MAC） on the physico-mechanical properties, cellmorphology, processing performance and thermal stability of foamed composites werecomparative analyzed. The mechanical measurements and ESEM test results indicated thatthe foamed composite with1%MAC had better physico-mechanical properties and smallercell size and better cell distribution compared with endothermic FA. And the processing andrheological performance of foamed composite adding1%MAC improved; and thedependence of apparent viscosity and shear rate got smaller; but dependence of apparentviscosity and temperature got larger and the viscous activation energy of the foamedcomposite with1%MAC was46.41KJ mol^-1. This was an increase of8.9%compared withthat of the non-foamed analogue. In addition, the thermal stability of this foamed compositeslightly decreased.Second focus of this work was to study the effects of maleic anhydride modifiedpolypropylene （MAPP）, silane KH570; aluminum zirconium TL-4and titanate DN301coupling agents on the mechanical properties, water absorption, surface wettablity,processing performance and thermal stability of foamed composites. With addition of coupling agents, the mechanical properties, water resistance and surface wettability allenhanced. The optimal amounts of these coupling agents were9%MAPP,2%KH570,1%TL-4and2%DN301. And the foamed composite with9%MAPP showed best comprehensiveperformance； although its thermal stability had a slightly decrease but the specificbending,tensile and the notched impact strength increased by23.1%,9.9%and47.8%andthe melt index （MI） increased from2.79g·10min^-1to3.61g·10min^-1. Followed with1%TL-4,the corresponding specific strengths increased by23.1%,9.9%and47.8%respectively andthe MI increased to4.50g·10min^-1and the thermal stability kept fine. Next was2%KH570，its corresponding specific strengths improved by7.1%,5.8%and24.9%respectively; but MIdecreased to2.55g·10min^-1and the thermal stability reduced. Last was2%DN301，itscorresponding specific strengths only raised by9.6%,6.8%and11.8%respectively; but MIincreased to3.99g·10min^-1and the thermal stability had a little enhancement.Moreover, in this part the influences of the type and dosage of coupling agent onthe the rheological properties about the bamboo powder/PP foamed composites were alsocarried out. By calculating the lgG’-lgf curve slopes in the low frequency region of thefoamed composites, the homogeneous degrees of composites before and after modificationwere measured. The relationship between viscosity and frequency of the foamed compositecould be fiitted by using the Cross model and the linear viscoelastic conversion betweendifferent solid particle fillers could be achieved through translation factor α（wt%）. And thechanges of the internal structure and relaxation process of foamed composites before andafter treatment were reflected by Han curve and the Cole-Cole diagram. Furthermore, thenon-Newtonian index of foamed composites was calculated using power law equation. Thestorage, loss modulus and complex viscosity all increased first and then decreasedwith the addition of coupling agents and in overall declined; and the homogeneous of foamedcomposites after modification increased. The lgG’-lgf slopes of nontreated composites was0.709and with addition of9%MAPP,2%KH570,1%TL-4and2%DN301the slopesincreased to0.782,0.758,0.842and0.811respectively. The coupling agents did notchange the non-Newtonian pseudoplastic characteristics of bamboo powder/PP foamedcomposite, but the Newton behavior enhanced with the increase of MAPP amount and thepseudoplastic behavior enhanced with the increase of KH570dosage and thenon-Newtonian index firstly increased and then decreased with the TL-4dosageincreased; while DN301had little effect on the non-Newtonian index of the foamedcomposite. The interface modification and chemical bonding mechanism of the foamed compositewas studied. Microscopic structures of foamed composites before and after modification wereanalyzed using environmental scanning electron microscopy （ESEM）; and molecular groupsand molecular structure of the untreated and treated bamboo powder were analyzed usingfourier transform infrared spectroscopy （FTIR）; and the surface element and chemicalbonding of foamed composites were investigated by X-ray photoelectron spectroscopyanalysis （XPS） and the crystal morphology of matrix and crystallinity of composites werecompared using X-ray diffraction analysis （XRD）.The maleic anhydride in the MAPP can etherified with the hydroxyl of the bamboopowder and thus the interfacial bonding force of bamboo powder and PP enhanced. Thesilanol of KH570and bamboo powder can formed-Si-O-C bonds during heating and henceinterfacial strength between bamboo powder and PP improved. TL-4with the hydroxyl of thebamboo powder had the chemical reaction and produced carboxyl and other organicfunctional groups and thus played an effective role in modifying and coating the surface ofthe bamboo powder. XRD results indicated that coupling agents did not affect the crystallinestructure of the matrix and the matrix of composites was all the α-crystalline PP; but thecrystallinity index of composites increased. The crystallinity degree of foamed compositewithout modification was21.05%; and increase to31.52%when adding9%MAPP.The third aspect was to optimize the injection molding technology and the amount ofbamboo powder by using a single factor experiments. The optimal injection parameters werethat the injection temperature of175℃^-190℃, mold temperatureof90℃, injection pressureof4.5MPa-6.5MPa, injection speed of40mm/s-70mm/s. The best amount of bamboopowder was50phr, which was33wt%, for its best comprehensive performance and lowermaterial price. When the bamboo powder was50phr, adding9%MAPP and1%MAC, theaverage cell diameter of the foamed composite was81.3μm and the cell density was2.66×107cell/cm3which was close to requirement of microcellular foaming. And the densitywas0.845g·cm-3, the bending modulus of2813.31MPa, the specific flexural, tensile andnotched impact strength of47.59MPa,26.12MPa and7.22KJ·m-2respectively. Comparingto its non-foamed composite, the density decreased by16.1%and the specific strengthsenhanced by16.8%-40.2%and the heat resistance also slightly improved. At the same time,the surface wettability of foamed composites was characterized by dynamic mathematicalmodel and the influences of coupling agents and bamboo powder amounts on the surfacewettability of foamed composites were investigated by using the coefficient K. When theamount of bamboo powder was50phr and with addition of9%MAPP, the initial contact angle of foamed composite in distilled water and glycerol were88.5°and91.5°respectivelyand the declining rate of contact angle that was K value of0.0071and0.0119respectively;and the surface free energy was34.19mJ·m-2.In the third part also research the impact of the bamboo powder content on therheological behavior of bamboo powder/PP foamed composite using a rotational rheometer.The foamed composite in the low frequency exhibited “solid-like behavior” and the storagemodulus, loss modulus and complex viscosity increased significantly with the bamboopowder content increased. The loss tangent （tanδ） slightly increased when thebamboo powder amount was10phr and30phr and following gradually increased with theincrease of the bamboo powder content. Both the zero shear viscosity and theCross characteristic relaxation time （λ） of the foamed composites increased with theincrease of bamboo powder content；while the Cross rate constant and non-Newtonianindex basically showed a decreasing trend.The forth aspect was to research on the influences of three different toughening fillerssuch as talc, POE and POE-g-MAH on the physico-mechanical properties, processingperformance, rheological properties and thermal stability of foamed composites. Whenadding8%POE-g-MAH, the33wt%bamboo powder/PP foamed composite showed the bestperformance and could replace PP in the field of automotive interior parts. At this point, thedensity of toughened foaming composite was0.849g·cm-3and the specific bending strengthof45.72MPa, flexural modulus of3019.91MPa, the specific tensile strength of25.22MPaand the specific notched impact strength of10.07KJ m-2and the vicat softening pointtemperature of155.8℃; and the MI was3.69g·10min^-1and the apparent viscosity was moresensitive to the shear rate; and had no effect on the thermal stability of foamed composite.The last aspect was to analyze the effects of the artificial accelerated aging and exteriornatural weathering on the bamboo powder/PP foamed composites with and without agingagents in view of color, thickeness, weight, flexural properties, tensile properties, notchedimpact strength and creep performance. And the short-term creep behavior of foamedcomposites before and after aging at25%,50%and75%stress levers was simulated withfour-component model and six-component model. By adding anti-oxidant B225and anti-UVagent UV770, the aging resistance of the foamed composite improved. However, afteraccelerated aging and natural aging for2160h, the color change△E*still were47and2.8;and the impact strength decreased by25.3%and9.2%, and the tensile strength slightlyenhanced by1.3%and6.0%respectively. The bending properties decreased by around13% after accelerated aging for2160h, and natural aging had little effect on the flexuralproperties. And after5400s creep test, the creep strain increased by1.2times; and theresidual retention of flexural performance were91.97%-97.70%and92.66%-98.87%,respectively.更多还原