木粉对聚乳酸流变、结晶及发泡行为的影响

以超临界CO_2为发泡剂,设计高温保压、低温快速泄压发泡的工艺,制备微孔发泡木粉/聚乳酸复合材料。利用X射线衍射仪、差示扫描量热仪、旋转流变仪对复合体系结晶及流变性能进行分析。采用排水法及扫描电镜研究了木粉含量对发泡材料表观密度、发泡倍率,泡孔密度及泡孔形貌的影响。结果表明,木粉的加入提高了木粉/聚乳酸复合材料熔体的复数黏度和储能模量,降低了聚乳酸的结晶度,提高了泡孔密度,减小了泡孔尺寸。当木粉含量为20%时,木粉/聚乳酸发泡材料表观密度为0.19g/cm~3,发泡倍率达到7倍,泡孔密度为7.23×10~8 cm~(-3),平均泡孔直径为20μm。     

聚丙烯/β-环糊精复合材料发泡性能及力学性能的研究

以β-环糊精(BC)为成核剂,通过微孔注塑发泡工艺制备了发泡聚丙烯(PP)复合材料。采用差示扫描量热仪(DSC)、扫描电子显微镜(SEM)等技术,研究了不同含量BC (0.25%～7%,质量分数,下同)对发泡聚丙烯复合材料发泡性能及力学性能的影响。结果表明:随着BC的加入,PP的发泡性能得到明显改善。添加7%的BC可以得到理想的泡孔形貌,泡孔直径为27.17μm,密度达1.23×10~7cell/cm~3。BC的加入使PP的结晶温度、结晶速率、粘度均有明显改善,有利于PP在更高温度下结晶并防止泡孔坍塌和并泡。与发泡聚丙烯材料相比,发泡PP/BC复合材料的拉伸、弯曲、冲击强度分别提高了21.2%、7%、12%。     

聚丙烯/纳米二氧化钛复合材料的超临界流体微孔发泡

以聚丙烯(PP)/nano-TiO2复合材料为研究对象,采用快速降压超临界微孔发泡技术,制备了泡孔密度、泡孔直径分别为2.8×107cell/cm3~3.15×109cell/cm3,46.36μm~6.08μm的PP/nano-TiO2微孔复合材料。研究了复合材料中nano-TiO2的质量分数、饱和压力及发泡温度对PP/nano-TiO2复合材料发泡行为的影响,通过扫描电镜(SEM)对微孔形貌进行表征。结果表明,加入nano-TiO2可以改善PP的发泡性能,并得到泡孔分布均匀的闭孔发泡材料;随复合材料中nano-TiO2质量分数由1%提高到5%,泡孔密度增加,泡孔直径减小。对于nano-TiO2质量分数为3%的PP/nano-TiO2复合材料,随着饱和压力的增加,泡孔直径和泡孔密度都增加;随着发泡温度的升高,泡孔密度减小,泡孔直径变大。     

弹性体对微发泡聚丙烯复合材料发泡行为的影响

以化学发泡为主线,在聚丙烯(PP)基体中添加弹性体三元乙丙橡胶(EPDM)制备微发泡聚丙烯复合材料。利用旋转流变仪、差示扫描量热法和扫描电镜等手段,系统地研究EPDM对微发泡PP材料发泡行为的影响。结果表明,EPDM的加入提高了PP材料的熔体强度,对PP材料发泡质量有明显改善;同时使PP复合材料的降温结晶峰向高温移动,能有效抑制泡孔的变形及并泡等恶化现象。当EPDM的质量分数为20%时,泡孔形态较为理想,其泡孔直径和泡孔密度分别为14.43μm,2.49×10⁷cm^-3。与未加EPDM的微发泡PP复合材料比较,EPDM的加入能够拓宽发泡PP复合材料的发泡温度窗口,发泡温度范围为180~195℃。     

滑石粉对微孔发泡木粉/聚丙烯复合材料结晶行为及泡孔结构的影响

以滑石粉为成核剂,超临界CO_2为发泡剂,采用间歇釜式方法制备微孔发泡木粉/聚丙烯复合材料。采用DSC、XRD和SEM对微孔发泡木粉/聚丙烯复合材料的结晶行为与泡孔结构进行了测定与分析。结果表明:滑石粉的添加能够提高微孔发泡木粉/聚丙烯复合材料的结晶温度,诱导产生不完善的α晶型;能够提高聚合物基体的熔体黏度,减小泡孔尺寸,增加泡孔密度,促使泡孔尺寸分布更均匀,最终能够形成泡孔密度为1.0×10~9个/cm~3、平均泡孔半径为16.4μm、发泡倍率为18倍、表观密度约为0.055g/cm~3的微孔发泡木粉/聚丙烯复合材料。     

EP含量对PP/PP-g-MAH/EP微孔发泡复合材料发泡行为及力学性能的影响

采用化学发泡法制备了聚丙烯/聚丙烯接枝马来酸酐/环氧树脂(PP/PP-g-MAH/EP)微孔复合发泡材料,研究了EP粉体含量对其发泡行为及力学性能的影响。结果表明,EP粉体在发泡过程中起异相成核作用,且与PP-g-MAH反应形成的交联网络结构提高了复合材料的熔体强度,从而显著改善了泡孔结构。随着EP含量增加,微孔发泡材料的拉伸强度、弯曲强度和冲击强度都呈现先增大后减小的趋势。当EP含量为5%时,复合材料的泡孔尺寸最小,泡孔密度最大,泡孔分布最均匀,微孔发泡材料的冲击强度最大;当EP含量为1%时,拉伸强度、弯曲强度最大,发泡材料的综合力学性能最佳。     

橡胶粒子对微发泡聚丙烯复合材料发泡行为与力学性能的影响

利用型腔体积可控注塑发泡装置制备微发泡聚丙烯(PP)/粉末橡胶复合材料,通过橡胶粒子的分散性以及复合材料的结晶行为,研究不同橡胶粒子对聚丙烯复合材料发泡行为和力学性能的影响。结果表明:橡胶粒子的加入使微发泡聚丙烯材料的泡孔分布细密而均匀,微发泡聚丙烯/马来酸酐接枝聚丙烯/粉末丁腈胶(PP/PP-MAH/NBR)复合材料的发泡质量较理想,其泡孔密度和尺寸分别为7.64×106个/cm3,29.78μm;综合泡孔结构和力学性能,微发泡聚丙烯/聚丙烯接枝马来酸酐/粉末羧端基丁腈胶(PP/PP-MAH/CNBR)复合材料的力学性能最优,与纯PP比较其冲击强度提升了2.2倍,拉伸强度仅仅降低了26%,是理想的微发泡复合材料。     

PP/PP-g-MAH/MMT纳米复合材料微孔发泡的研究

通过熔融共混法制备聚丙烯/马来酸酐接枝聚丙烯/蒙脱土(PP/PP-g-MAH/MMT)纳米复合材料母粒。利用"二次开模"法注塑成型制得PP/PP-g-MAH/MMT纳米复合微孔发泡材料。研究了MMT和PP-g-MAH的用量对纳米复合微孔发泡材料发泡质量的影响。结果表明:5%的MMT和6%的PP-g-MAH有较好的协同效应,微孔发泡材料发泡倍率最大,泡孔平均直径最小,泡孔密度较大,泡孔尺寸分布范围较窄。     

三相存在下聚丙烯/纤维复合发泡材料的力学性能

采用密炼方式分别制备碳纤维(CF)、玻璃纤维(GF)、芳纶纤维(AF)增强聚丙烯(PP)母粒,通过注塑成型制备相应的聚丙烯/纤维复合发泡材料,研究了3种纤维对微发泡聚丙烯/纤维复合发泡材料力学性能的影响。结果表明,PP/CF复合发泡材料的综合性能提高的幅度最大,其中拉伸、压缩、弯曲强度分别提高了100.9%,80.4%,126.5%;PP/AF复合发泡材料的韧性最好,相对于纯PP提高了151.2%;并且,PP/CF复合发泡材料的泡孔参数最好,泡孔尺寸为28.97μm,泡孔密度为8.58×106cm~(-3),泡孔尺寸分布达到9.22μm。     

iPP/PET原位微纤复合材料的超临界二氧化碳发泡行为EI北大核心CSCD

利用微纳层叠共挤技术中独特的剪切拉伸复合流动场作用实现聚对苯二甲酸乙二醇酯(PET)在聚丙烯(i PP)中的原位微纤化,研究了PET的原位微纤化对i PP/PET复合材料发泡行为的影响。扫描电子显微镜结果显示,经过微纳层叠共挤装置挤出后,PET在i PP中形成直径为0.2~1μm的微纤。PET微纤化显著地改善了i PP的结晶性能、流变性能及发泡性能。差示扫描量热测试结果表明,PET微纤对i PP具有明显的异相成核作用,能提高i PP的结晶温度和熔点;拉伸流变行为分析发现,PET微纤的形成使得i PP产生明显的应变硬化现象;通过超临界二氧化碳发泡发现,i PP/PET原位微纤复合材料的泡孔比纯i PP更加稳定,尺寸更小,密度更大,且泡孔内存在三维微纤网络结构。     

微发泡聚丙烯/晶须复合材料的发泡行为与力学性能

将改性的MgSO4和CaCO3晶须加入聚丙烯中,在二次开模条件下制备微发泡聚丙烯(PP)/晶须复合材料,通过晶须在基体中的分散性、泡孔直径大小分布和泡孔密度,分析了不同晶须对材料的发泡行为与力学性能的影响.结果表明,晶须具有一定成核效应,CaCO3晶须的泡孔尺寸25.27μm左右,填充增强效果差;MgSO4晶须的泡孔尺...     

木粉/聚丙烯木塑复合泡沫材料吸能特性

采用模压法制备木粉/聚丙烯复合泡沫材料,并对不同木粉含量的泡沫材料进行静态压缩、循环压缩、压缩蠕变、动态热机械分析的测试,探讨了不同木粉含量的木粉/聚丙烯复合泡沫材料的能量吸收效果。结果表明: 随着木粉含量的增加,木粉/聚丙烯木塑复合泡沫材料的能量吸收量、能量吸收效率参数、松弛率、循环损耗量、动态力学性能等均呈先升后降的趋势,在木粉质量比为30%时泡沫材料吸能性能达到最佳。     

Effect of flame retardants on mechanical properties,flammability and foamability of PP/wood–fiber composites

The mechanical properties, flame retardancy, thermal degradation and foaming properties of wood–fiber/PP composites have been investigated. Ammonium polyphosphate (APP) and silica were used as flame retardants. The limiting oxygen index (LOI), thermal gravimetric analysis (TGA) and cone colorimeter (CONE) were employed for the study of fire retardance. At the same time, wood–fiber/PP composite foams were produced with the batch foaming technique using CO₂ as blowing agent. The effects of APP and silica content, pressure and temperature on the final cell structure were investigated. According to LOI, TGA and cone calorimeter results obtained from the experiments, APP and silica are effective flame retardants for wood–fiber/PP composites, and silica was shown to have a flame retardant synergistic effect with APP in wood–fiber/PP composite. The mechanical properties of the composites decreased with addition of flame retardants, except for the tensile strength of small amount of silica filled wood–fiber/PP composite. The results also revealed that the cellular morphologies of the foamed wood–fiber/PP composites are a strong function of the content of APP and silica as well as foaming conditions.     

Effect of nano-Calcium Carbonate on microcellular foaming of polypropylene

Using supercritical carbon dioxide as the physical foaming agent, a new batch process was carried out to prepare microcellular polypropylene (PP) and polypropylene/nano-Calcium Carbonate (PP/nano-CaCO₃) foams. Four concentrations of nano-CaCO₃, 3, 5, 7, and 10 wt% were used. The cell structure of foams and advantages of this new process were investigated and explained by thermal properties. Results showed that the foamed PP/5 wt% nano-CaCO₃ produced a microcellular foam with the minimum mean cell diameter (9.55 μm) and maximum cell density (1.50 × 10⁹ cells/cm³) among the four blends. Some unfoamed regions were observed in nanocomposite foams because nano-CaCO₃ could accelerate crystallization in cooling and cryostat stage. The new process took much less time (2.5 h) to foam and had much broader foaming temperature range (about 55 °C). But the foaming temperature range decreased after blending nano-CaCO₃ into PP matrix because nano-CaCO₃-induced isothermal and non-isothermal crystallization at higher temperature. In addition, the cell growth effect on variations of volume expansion ratio in PP/nano-CaCO₃ nanocomposites could be neglected comparing with the heterogeneous cell nucleation effect.     

Effects of extruder parameters and silica on physico-mechanical and foaming properties of PP/wood-fiber composites

In this study, the effects of screw configuration, screw speed and silica content on the physico-mechanical and foaming properties of PP/wood-fiber (WF) composites were investigated. PP/WF composites were produced by the intermeshing co-rotating twin screw extruder. Microcellular closed cell PP/WF composite foams were prepared using pressure-quench batch process method. Firstly, an attempt has been made to determine the optimum conditions of extrusion that involve screw configurations and screw speed. The mechanical properties and morphology results showed that PP/WF composite prepared under the configuration C at screw speed of 150 rpm have higher mechanical properties, and narrower cell size distribution caused by uniform dispersion of wood fiber. And then, under the optimal processing conditions, the effect of silica content on the physico-mechanical properties of PP/WF composite, the final cell morphology as well as the relative density of the foamed PP/WF/Silica composites is studied.     

微孔聚丙烯的分形特征

泡孔结构具有分形特征,可以用分形维数来描述其形态复杂性。文中应用MATLAB编写的数盒子算法,计算了应用超临界二氧化碳作为发泡剂间歇发泡制备的微孔聚丙烯的盒维数,并讨论了二值化阈值对分形维数的影响。结果表明,聚丙烯微孔结构具有典型的分形特征,分形维数与微孔聚丙烯的泡孔密度有关,在一定阈值下,分形维数随着泡孔密度的增加而增加。分形维数是发泡聚丙烯微孔结构的几何特性之一,体现了聚丙烯在特定条件下的发泡能力。