羟基不饱和脂肪酸改性纳米碳酸钙对聚丙烯微观形态和流变性能的影响

EFFECT OF UNSATURATED HYDROXYL-FATTY ACID MODIFIED NANO-CaCO_3 ON THE MORPHOLOGY AND RHEOLOGY OF PP

采用羟基不饱和脂肪酸,通过固相法对硬脂酸改性的工业纳米碳酸钙CCR进行表面改性制备了R-CCR,红外光谱(FTIR)显示改性剂已结合在碳酸钙表面.通过熔融共混法制备了聚丙烯(PP)/乙丙橡胶(EPDM)/纳米碳酸钙二元和三元复合材料.并利用扫描电子显微镜(SEM)和透射电子显微镜(TEM)观察复合材料的微观形态,发现R-CCR的加入,使PP复合材料的拉伸断面出现明显的拉丝状结构和大面积的屈服变形,与PP/EPDM/CCR相比,PP/EPDM/R-CCR冲击断面的空穴明显增加并细化,R-CCR在PP基体中分散均匀,且界面模糊,与基体的相容性明显优于CCR.复合材料流变行为的研究表明R-CCR的加入,体系储存模量G′和损耗模量G″随频率的增加而增加,对损耗因子和复数粘度的影响不大;但PP/EPDM/R-CCR复合材料的表观粘度,明显低于PP/EPDM/CCR和纯PP,同时,剪切速率的增加可有效降低体系的表观粘度.力学性能表明,R-CCR对PP同时起到增韧和增强的效果.且R-CCR和EPDM对PP具有协同增韧的效果.在保持聚丙烯的模量和强度基本不变的前提下,大幅度的改善聚丙烯的韧性,同时加工性能保持不变.

A modified nano-calcium carbonate （R-CCR） was prepared by coating a layer of unsaturated hydroxyl-fatty acid on the surface of CCR powders using a solid state method, the latter were commercial nano-CaCO3 modified with stearic acid. FTIR studies indicate that the modifier is combined on the surface of CaCO3. PP/EPDM/nano- CaCO3 ternary composites are prepared by a melt-mixing method. SEM and TEM are utilized to examine the morphology of the composites. The tensile fractured surface of PP/EPDM/R-CCR shows a fibroid morphology andlarge-scale yield deformation. The impact fractured surface shows that the amount of cavities in PP/EPDM/R-CCR systems is increased and their size diminishes obviously. R-CCR particles were dispersed uniformly in PP matrix, and their compatibility was distinctly improved as compared with CCR as the amount of R-CCR was 15 phr. The tensile strength remains nearly constant （reduces from 27.6 MPa to 27.5 MPa） while the impact strength increases from 9.6 kJ/m^2 to 15.6 kJ/m^2 as CCR is replaced by R-CCR. Meanwhile the flexural strength and flexural modulus arealso increased correspondingly. Furthermore,the impact strength of PP/EPDM/R-CCR keeps on a high level （15.6 kJ/m^2） which is more than the sum of that of PP/EPDM and PP/R-CCR （6.63 kJ/m^2 and 6.04 kJ/m^2 respectively）. It indicates the R-CCR and EPDM has significant synergistic toughening effect on PP, keeping the strength, modulus of virgin PP as well. Both the storage modulus G′ and loss modulus G＂ of PP/EPDM and PP/EPDM/R-CCRcomposites increase with increasing frequency, but the values of G′ and G＂ of the tertiary composite are relatively in a higher level than that of the binary system. The loss factor and viscosity decrease with increasing frequency but there has little difference between tertiary and binary composites. The apparent viscosity η of the tertiary system containing R-CCR is lower than that of tertiary system containing CCR and virgin PP. The viscosity of compositesignificantly decreases with increasing shear rate. The measured mechanical properties of the composites indicate that replacing of CCR by R-CCR for binary composites could simultaneously enhance the toughness and strength of PP.