Preparation Of Expandable Polypropylene Particle

This paper is a part of the summaries of study work for "Bead foaming technology of uncross-linked polypropylene (PP)", a project of the "Scientific Research Project of Guangdong Province". Part 1 is a study that prepares the expanded polypropylene particle (EdPP), taking supercritical CO₂ as blowing agent through fast pressure drop method; Part 2 is to optimize preparation technology of EdPP with adding nano-nucleating agent; Part 3 is to optimize preparation technology of EdPP with adopting original bubble nucleus; Part 4 is about the preparation of the expandable polypropylene particle (EbPP), which is made using self-made carrier type blowing agent through fast heating method.Polypropylene foaming material has been getting important application in many fields such as packing and intra-decorate of automobile and heat insulation materials and so on, Because of its excellent thermal stability, well enduring environmental stress crack, good enduring chemical corrosion, good degradation performance, high tensile strength and anti-impact properties. The structural characteristic of polypropylene makes its foaming course hard to be controlled and this has affected the process of its large-scale industrialization. This paper first studies the preparation technology of EdPP, then optimizes preparation technology of EdPP by modifying means ulteriorly, eventually, gains EbPP using carrier type blowing agent self-made.1. The preparation technology of EdPP. (1) Along with foaming temperature increases step by step, the density of foaming material first reduces and then increases, there is a minimal value at 130℃with a density of 0.07g/cm³; but the cell density of foaming material first increases and then reduces, the maximum density is 1.01×10⁹cells/cm³ occurred at 130℃as well. (2) Along with the increase of saturating pressure, the foaming material density decreases according to the index law approximately, while the cell density increases according to the index law approximately. (3) In the solidifying stage, the suitable and effective cooling is necessary for resin matrix, the ice-water-cooling way is strongly recommend.2. Optimizing the preparation technology of EdPP with the nano-nucleating agent. (1) Though the nano-nucleating agent which is scattered with "dissolving method" can improve the foaming effect of polypropylene resin pellets efficiently, its scattering effect is still not very ideal and there are some baffling problems to be sovled urgently, for example, the recrystallization of polypropylene resin is not very complete and the nano-silicon deoxidize is partly remained in the naphthalene tetra-hydrogen and so on. (2) The foamed material density decreases with the increase of PHR of the nano-nucleating agent, when the nano-nucleating agent is 3PHR, its value is 0.06g/cm³; however, the cell density of the foamed material increases, its value is 1.29×10⁹cells/cm³ at the same PHR of the nano-nucleating agent.3. Optimizing the preparation technology of EdPP with the original bubble nucleus. (1) The fluid wax could be separated from the polypropylene resin with gasoline solvent and its effect is comparatively ideal. (2) The density of foaming material first reduces and then increases with the increase of PHR of the fluid wax, there is a minimal value at 2PHR of the fluid wax with a density of 0.05g/cm³; but the cell density of foaming material first increases and then reduces, the maximum density is 1.36×10⁹ cells/cm³ occurred at 2PHR as well. (3) Even if the foaming temperature and the saturating pressure are both low and there is not any cooling means, the polypropylene particle that contains original bubble nucleus can also foam successfully only with the suitable pressure drop speed, so, it should be regarded as EbPP.4. The preparation technology of EbPP. (1) In the three kinds of the chosen carrier type blowing agent, the10Xmolecular sieve blowing agent meets the requirement of polypropylene particle foaming technology best, its maximal out-gassing quantity is 47.60ml/g with the maximal utilization rate as high as 95.71%; the out-gassing quantity is 18.4 ml/g after 300 seconds de-sorption at 130℃with the utilization rate of 30.7%. (2) When the10X molecular sieve blowing agent is 6PHR, the best foaming effect can be got which the density of foaming material is 0.11g/cm³ with the cell density of 2.15×10⁶cells/cm³. (3) Stored after one week, EbPP still can be foamed, the foaming material density is 0.25g/cm³ with the cell density of 1.48×10⁶cells/cm³, and all foaming pellets are relatively soft; however, stored after one month, the carrier type blowing agent becomes invalid and makes EbPP cannot be foamed any more.