Researches On The Melt-Performance Improvements And Foaming Behavior Of Polypropylene By Nano-Clay Compounding

Polypropylene (PP) has been becoming a hotspot in the field of foam plastics, due to its good thermal stability, high mechanical property, soft and pleasant surface, and excellent adaptability of microwave. However, the seriously congregating phenomenon, as well as most open cells, occurs in the foam structure of conventional polypropylene (CPP). In contrast, the more and better closed cells can be obtained in the foam structure of the high melt strength polypropylene (HMSPP). Therefore, it is need to modify the CPP properties, improve the melt strength, in order to exalt its competence in the application of foam plastics. As known, polymer/MMT nanocomposites have advanced melt viscosity and modulus. If polymer/MMT nanocomposites could be used to enhance the melt viscosity and modulus of CPP, and could help CPP to foam in the popular equipments, the economic and practical significance will be far-propound.In this article, based in the PP matrix and MMT filler, the structure and property of PP/MMT nanocomposites, as well as the chemical foaming behavior are studied. The main contents and conclusions are listed below:1. Effects of clays with different organic modification on on the clay layers dispersion, as well as the structures and properties of copolymerized polypropylene (cPP)-clay composites, were studied by first calculating the activation energy of different cPP relaxations. The main conclusions are as following: (1) The interspacing of the clay layers increased with the increasing of the spatial effect of the substituent surrounding with the N+ in the alkylammonium ion (CH3-(CH2)n-NH3+). However, the organoclay modified by 2C18 alkylammonium, which weakened their interaction with cPP molecules, and made its composites hardly differ from the cPP matrix. (2) Effects of different organic modifications on theα- andβ-relaxation of cPP molecules in cPP-clay composite, was related with the interactions of cPP molecules and clay layers. The organic modification and content of clay had little effect on theγ-relaxation of cPP.2. Effects of the clay content on the structure and melt rheological property of cPP-clay nanocomposites by rheological technology and WAXD were extensively studied.Research results showed that the structure stability of cPPCNs melts was directly relative to the dispersion of clay layers in cPP matrix, which was stable at 3-5wt% clay loadings, ascribed to the good dispersion of clay layers, and gave rise to a strong low frequency solid-like response (G'> G''). Such this solid-like response was strengthened with the clay loading increasing. The mobility of cPP molecular chains were restricted by clay layers, and this restriction effect attained maximum when the content of clay was 5wt%.3. The miscibility of cPP molecules and clay layers, the structure and property of PP-clay composites, was studied by first using MAH-g-POE as compatibilizer. The results showed that addition of MAH-g-POE could improve the dispersion of clay layers in PP matrix and the interaction between PP molecules and clay layers attained a maximum at presence of 10wt%. The pseudo-solidlike rheological response at the low frequencies was relative with not only the miscible role of MAH-g-POE, but also the self-elasticity of MAH-g-POE.4. As reference of an expandable high melt strength PP (HMSPP), a conventional PP(CPP) which owned similar physical parameter to HMSPP was selected, and by use of the synthetic role of nanoclay and compatibilizer, the melt rheological feature of CPP was improved to approach to that of HMSPP. Moreover, the foaming behavior of CPP-clay composites was investigated. The main results are as following: (1) The nanoclay compounding might improve the melt rheological character of CPP, approaching to that of HMSPP. The cPP-clay composites with MAH-g-EPDM and MAH-g-POE exhibited similar melt rheological characteristics as HMSPP, with a relatively high melt modulus at low frequency. (2) The 5wt% clay was enough to enhance the low-frequency modulus of the CPP-clay system. (3)By one-step compression molding, the CPP foam is still far from HMSPP foam in quality, and the HMSPP foam owned relatively uniform size of abscess and a high abscess amount every unit area, suggesting a better abscess structures. (4) By one-step compression molding, the foam quality of CPP/MAH-g-POE/DK1 with a fixed clay content of 5wt%was improved as the loading of MAH-g-POE increased from 5wt% to 15wt%,which should be attributed to the improvement of the uniformity of clay dispersion in CPP-clay composites, as well as the enhancement of the low frequency viscosity and modulus. (5) By one-step compression molding, CPP/MAH-g-POE/DK1(85/10/5) with 5wt% AC blister might acquire good foam with uniform abscess size, and shows similar foam structure to that of HMSPP/AC(100/10). (6) The system of CPP/MAH-g-POE/DK1(85/10/5) with 5wt% AC, by using suitable condition of extrusion foaming technique, could obtain a good foam plastics, the cell was small and dense, about 400μm.