Preparation of high expansion ratio polypropylene foam
Key height-adjusting strength PP polypropylene polypropylene high foaming ratio due to polypropylene (PP) has high tensile strength, yield strength, rigidity and strong chemical chemistry and high temperature (130X: Above), it has become a new type of foam material with more application value and market potential after polystyrene, polyester and polyethylene foam materials. However, PP is a linear crystalline polymer, and the molecular chain is less 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 escape, cell collapse, bubble merger, etc., volume strength (r resin) and HMSPP/PP blend system (2" resin The melt strength (as shown) found that the melt strength of HMSPP is relatively high, basically maintained at about 0.9, while the melt strength of the blend system (2 resin) is between 0.60.7 N, which is usually a relatively fine melt. The strength can ensure the strength of the bubble wall and stabilize the gas and strengthen the bubble: but at the same time, this strong resistance to deformation limits the expansion of the bubble. HMSPP has too high melt strength, so that the second effect As a result, the diameter of the bubble becomes small, the wall of the bubble is extremely thick, and the expansion ratio of the product is lowered. While the melt strength of the blend system (2 resin) is suitable, a foam having a uniform appearance and a uniform internal structure is obtained.
2.1.3 Storage modulus and loss modulus are visible and visible. The storage modulus and loss modulus of 1 resin are higher than 2s resin. This indicates that the long-chain branched structure of HMSPP requires a longer relaxation time at any lower or higher shear rate, and the molecular chain is too late to be entangled. Therefore, it shows that HMSPP has high rigidity, which also limits its deformation, which is one of the reasons why it is difficult to form a product with thin bubble walls and uniform cells. By comparing the melt flow rate, melt strength, storage modulus and loss modulus of the two systems, it can be seen that HMSPP has a high resistance to deformation, which hinders the deformation of the matrix during gas expansion. Therefore, foaming becomes difficult, and a product having small cells and a thick cell wall is obtained. By blending HMSPP with PP, the melt strength and modulus of the system can be significantly reduced, so that a suitable foaming system is obtained. When HMSPP and PP are blended at a ratio of 7:93, the foaming performance of the system is good. A product having a density of about 0.12 g/cm 3 , a uniform cell, and a regular appearance was obtained.
2.2 The relationship between the additive and the density of the foamed product 2.2.1 The relationship between the chemical foaming agent content and the density of the foamed product. Adding different amounts of foaming agent (as shown) in the 2 matrix resin, it can be found that When the content of foaming agent is increased, the density of the product is first decreased and then increased. The product with the lowest density is obtained at 23 parts by mass of the foaming agent, and the reason for the uniform distribution of the cell structure is that the foaming agent is excessively distributed. , will cause agglomeration, which will cause uneven pores; second, the generated gas will plasticize the matrix: Third, the foaming agent will release a lot of heat during the decomposition process, too much foaming agent Will cause too much exotherm, resulting in a decrease in the strength of the PP resin matrix, causing the cell to collapse and the cell wall to rupture; in addition, too much foaming agent will cause a huge squeeze on the cell wall when the cell is expanded adjacent to the cell. It may also cause the bubble wall to rupture, and as a result, the density of the product gradually increases. Therefore, the amount of the blowing agent is preferably from 2 to 3 parts by mass.
2.2.2 Relationship between nucleating agent content and density of foamed products In the foaming process, it is often necessary to add a nucleating agent to form more bubble nuclei. Typical nucleating agents are particles (such as metal particles, metal oxides and hydroxides thereof) uniformly distributed in the body. The addition of a nucleating agent can provide a bubble-forming interface, which is more likely to form a bubble nucleus and homogenize the cell P81. In the case of a 2-base resin, as the nucleating agent content increases, the density of the product first decreases sharply. Gradually rising again. This indicates that adding a small amount of nucleating agent to the system will increase the cell density and increase the expansion ratio. However, with the further increase of the nucleating agent content, the density of the product will increase. The reason may be that the nucleating agent is too Many, and its size is extremely small, prone to agglomeration, resulting in the formation of large cells, and the phenomenon of cell merger, so the product density has increased. Therefore, the optimum amount of nucleating agent is 02-0.3 quality children.
Relationship between nucleating agent content and product density 3 Conclusion The melt strength of the control system is within a suitable range (about 0.60.7 N), and a system with good foaming performance can be obtained, and the density of the foamed product is obtained. Around 12g/cm3, and the cell distribution is uniform.
The content of the chemical foaming agent in the system is preferably controlled to 2 to 3 parts by mass. It can avoid the phenomenon that excessive foaming agent emits a large amount of heat during decomposition to cause cell collapse and gas escape.
(Finish)
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