Effect of nano-montmorillonite on foaming properties of wood flour/polypropylene composites
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摘要: 采用高压釜间歇式发泡法，结合超临界CO2微孔发泡技术制备了发泡木粉-纳米蒙脱土(NMMT)/聚丙烯(PP)复合材料。通过对复合材料的结晶行为、流变性能、泡孔形貌及压缩性能进行分析，主要研究了NMMT对其微孔结构及力学性能的改善作用。结果表明：NMMT的引入使木粉/PP复合材料中PP基体的结晶速率加快，结晶度减小，有利于发泡均相体系的形成和泡孔生长；PP分子链的运动受到NMMT片层的抑制作用，导致木粉/PP复合材料的熔体弹性提高，泡孔合并与塌陷的现象减少，发泡材料的平均泡孔直径从30.4 μm降低至20.3 μm，并且泡孔尺寸的均匀性得到明显改善，压缩强度和模量分别提高了187%和223%。Abstract: The foamed wood flour-nano-montmorillonite (NMMT)/polypropylene (PP) composites were prepared by the batch foaming method using supercritical CO2 microcellular foaming technology. Effects of NMMT on the microcellular structure and mechanical properties of the composites were explored by investigating crystallization behavior, rheological properties, cell morphology and compression properties. The results show that NMMT accelerates the crystallization rate of the PP matrix in the wood flour/PP composites, and reduces the crystallinity rate. This is beneficial to the formation of foamed homogeneous system and cell growth. The PP molecular chain is inhibited by the NMMT interlayer, resulting in the melt elasticity increasement of the wood flour/PP composites. The phenomena of cell coalescence and collapse are reduced, the average cell diameter of the foamed composites is decreased from 30.4 μm to 20.3 μm, and the uniformity of cell size is obviously improved. The compressive strength and modulus are increased by 187% and 223%, respectively.
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图 1 间歇式微孔发泡实验装置图
Figure 1. Diagram of the experimental setup used for the batch microcellular foaming process
图 2 纳米蒙脱土(NMMT)与NMMT-马来酸酐接枝聚丙烯(MAPP)/聚丙烯(PP)复合材料的XRD图谱
Figure 2. XRD patterns of nano-montmorillonite (NMMT) and NMMT-maleic anhydride grafted polypropylene (MAPP)/polypropylene (PP) composites
图 3 PP、杨木粉(WF)/PP复合材料与WF-NMMT/PP复合材料的XRD图谱
Figure 3. XRD patterns of PP, wood flour (WF)/PP composites and WF-NMMT/PP composites
图 4 未发泡PP、WF/PP复合材料与NMMT-WF/PP复合材料的DSC结晶曲线
Figure 4. DSC crystallization curves of unfoamed PP, WF/PP composites and NMMT-WF/PP composites
图 5 未发泡PP、WF/PP复合材料与NMMT-WF/PP复合材料的DSC升温曲线
Figure 5. DSC heating curves of unfoamed PP, WF/PP composites and NMMT-WF/PP composites
图 6 未发泡PP、WF/PP复合材料与NMMT-WF/PP复合材料的相对结晶度随时间变化曲线
Figure 6. Relative crystallinity of unfoamed PP, WF/PP composites and NMMT-WF/PP composites versus crystallization time
图 7 PP、WF/PP复合材料与NMMT-WF/PP复合材料的储能模量
$G'$ (a)、损耗模量$G'' $ (b)、复数黏度$\eta ^*$ (c)、损耗角正切值${\rm{tan}}\delta $ (d) 随角频率$\omega $ 变化曲线Figure 7. Storage modulus
$G'$ (a), loss modulus$G'' $ (b), complex viscosity$\eta ^*$ (c) and loss tangent${\rm{tan}}\delta $ (d) curves with angular frequency of PP, WF/PP composites and NMMT-WF/PP composites
图 8 发泡WF/PP复合材料与发泡NMMT-WF/PP复合材料的表观密度和发泡倍率
Figure 8. Density and expansion ratio of foamed WF/PP composites WF/PP composites and NMMT-WF/PP composites
图 9 发泡WF/PP复合材料 (a) 与发泡NMMT-WF/PP复合材料 (b) 的SEM图像，WF/PP复合材料 (a′) 与发泡NMMT-WF/PP复合材料 (b′) 的直方图，发泡WF/PP复合材料 (a′′) 与发泡NMMT-WF/PP复合材料 (b′′) 的泡孔生长示意图
Figure 9. SEM images of fracture surface of foamed WF/PP composites (a) and foamed NMMT-WF/PP composites (b), frequency histogram of foamed WF/PP composites (a′) and foamed NMMT-WF/PP composites (b′), cell growth schematic diagram of foamed WF/PP composites (a′′) and foamed NMMT-WF/PP composites (b′′)
图 10 发泡WF/PP复合材料与发泡NMMT-WF/PP复合材料压缩应力-应变曲线
Figure 10. Compressive stress-strain curves of foamed WF/PP composites and foamed NMMT-WF/PP composites
表 1 未发泡PP、WF/PP复合材料与NMMT-WF/PP复合材料的熔融峰温度、熔融焓和结晶度
Table 1. Molten peak temperature, melting enthalpy and crystallinity of unfoamed PP, WF/PP composites and NMMT-WF/PP composites
Type Melting
peak/℃Melting enthalpy/
(J·g−1)Crystallinity/
%PP 160.4 71.6 34.2 WF/PP 163.8 68.6 41.0 NMMT-WF/PP 164.6 53.5 34.5 
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