PS powder GPPS fine powder Polystyrene powder SMC BMC fiberglass high transparency low shrinkage additive LPA

Polystyrene powder has good processing performance for unsaturated polyester resin, suitable for various molding processes such as SMC compression, BMC injection, pultrusion, RTM, hand lay-up, and casting. However, during the product manufacturing process, issues like cracks in the resin phase, surface quality defects, and dimensional control problems may occur. The main reason for these issues is that during polymerization, the resin units tend to pack tightly and form nuclei, leading to phenomena of polymerization shrinkage and thermal shrinkage. The internal stress caused by shrinkage leads to the resin sinking inward from the surface, and this depression propagates from the surface to the center, releasing internal stress until equilibrium, directly causing the occurrence of defects. The role of low-profile additives (LPA) is to locally relax and release internal stress, compensating for polymerization shrinkage, thereby reducing the shrinkage rate. Non-polar low-profile additives, represented by polystyrene (PS), also include solid powders such as polyethylene (PE) and polypropylene (PP). These types of low-profile additives form a two-phase system with the resin before it cures, simply utilizing the thermal expansion of thermoplastic resins to inhibit curing shrinkage. Such low-profile additives have good inherent colorability but generally average low-shrink performance. The mechanism of action for low-profile additives is based on phase separation, where post-curing phase separation with the resin is a necessary condition for generating voids and resisting shrinkage. The specific action process is as follows: [2] ① The material heats up and begins to thermally expand; ② An increase in temperature causes the initiator to decompose, initiating curing; ③ From being compatible with the resin, they become incompatible, starting to form two phases; ④ The reactive low-profile additive and resin gather within the thermoplastic; ⑤ As the polymerization progresses, along with an increase in temperature and the degree of polymerization, the resin phase shrinks with rising temperature, while the volume occupied by the low-profile additive and unreacted monomers increases, compensating for the polymerization shrinkage; ⑥ The monomer in the low-profile additive phase begins to react, producing micro-voids due to the stress from polymerization; ⑦ Finally, cooling starts. Above the Tg of the resin phase, the thermal expansion coefficients of the low-profile additive phase and the resin phase are roughly equal. Below the Tg of the resin phase, the cold shrinkage of the resin phase is much less than that of the low-profile additive phase. This difference in cold shrinkage leads to the generation of micro-voids in the low-profile additive phase, similar to those generated around the low-profile additive phase due to stress, until the Tg of the low-profile additive is reached. Our company offers PS powder, LDPE powder, HDPE powder, SBS powder, PMMA powder, and other additives, suitable for SMC compression, BMC injection, pultrusion, RTM, hand lay-up, and casting.