Oil Chemical Co., Ltd. Beijing Institute of Chemical Engineering, material science, research direction for polymer modification. Tel: (010) Polypropylene (pp) has high tensile strength, rigidity and strong chemical corrosion resistance and high service temperature, so it is followed by polystyrene, polyurethane and polyethylene foam materials. New foam materials with more application value and market potential. However, pp is a linear crystalline polymer, and the molecular chain is rarely branched, so the viscosity of the pp resin decreases as the temperature increases. When the temperature exceeds the melting point, the melt strength drops sharply, which is likely to cause bubble wall cracking, gas escaping, cell collapse, and bubble merging during the foaming process. It is prepared by grafting PP with cobalt source, the gel content is 20%, MFR is about 0 089g/10min. HMSPP is foamed separately or blended with PP matrix resin. The foaming performance of the system is Different.
It can be seen that when the SPP is used alone, the foam wall of the product is thicker and the density is larger; and the HMSPP and PP resin are thinner than the 7:93 product, forming a closed-cell structure, the appearance is regular, and the density is about (mass ratio) mixing. (4 = resin), the foaming performance of the system is good, 012g / on3. This work compared the MFR of different systems. As can be seen from Table 1, the MFR of HMSPP is extremely low. This is because the internal long chain branch is more, the molecular chain migration takes a long time, and the deformation is slower.
This limits its expansion and deformation in a short period of time during the foaming process, making it difficult to form larger cells.
Table 1 MFR ens resin number of high melt strength series resin HMSPP content mass part PP content / mass part MFR / 1 = melt strength curve of resin and 4 resin From the visible, the melt strength of HMSPP is higher, basically maintained at Q Around 9N. This strong anti-fracture performance, on the one hand, ensures the strength of the bubble wall, and stabilizes the gas and solidifies the bubble; on the other hand, this extremely strong resistance to deformation limits the expansion of the bubble. Excessive melt strength causes the second action to be highlighted, resulting in a smaller bubble diameter, a thicker cell wall, and a lower product expansion ratio. Blending PP with HM SPP and adjusting the melt strength of the system in Q6~Q7N can obtain a foam material with uniform appearance and uniform internal structure. The density of the product is higher than 4=resin. This indicates that at the lower or higher shear rate, the long-chain structure of HMSPP requires the pine 2 resin number PP content mass part LDPE content mass part 51005610010710015 3 relationship between the nucleating agent content and the product density in foaming In the process, it is necessary to add a nucleating agent to provide an interface for forming bubbles, which is easier to form a bubble nucleus and to make the cells uniform. 5 Lu Yujie, Qiao Jin, Lu Lixin. Progress in research and development of high melt strength polypropylene. Synthetic resin and plastic, 2 (1) Q17 (4): 3Q326 Gao Jianming, Zhang Xiaohong, Liu Yuqun and so on. Preparation of high melt strength polypropylene. Beijing: Chemical Industry Publishing 8 Yin Zhenduo, Li Yanyun. Development of new propylene nucleating agents for functional additives. Journal of Beijing Institute of Petrochemical Technology. 2QQ412(4)2Q25(Edit: Song Yuchun) The melt strength of PP and its blending system PP is good at tensile rate of 200~400mm/s, and it is maintained at Q55~Q60N (for example). Therefore, in the foaming process, when the foaming agent is thermally decomposed to generate a large amount of gas, the necessary melt strength can be well maintained to ensure the strength of the foam wall, whether in the initial stage of the reaction or in the subsequent stage of intense reaction. The gas is wrapped, so that the more uniform knotted product appears white. Copolymerization 2 was used for a long time, and the molecular chains were too late to be entangled. Therefore, it shows a high rigidity, which also limits its deformation. This is also why it is difficult to foam.
(Finish)
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