Food Grade Rigid HIPS Plastic Sheet Roll For Thermoforming Food Trays

Polystyrene (Polystyrene, abbreviated PS) refers to a polymer synthesized from styrene monomer through radical addition polymerization reaction, the chemical formula is (C8H8)n. It is a colorless and transparent thermoplastic with a glass transition temperature higher than 100°C, so it is often used to make various disposable containers that need to withstand the temperature of boiling water, and disposable foam lunch boxes.
Impact-resistant polystyrene is an amorphous polymer formed by graft polymerization of styrene monomer and rubber, or a physical blend of polystyrene and rubber (usually polybutadiene rubber). The resulting polymer has toughness, usually white (there are also transparent grades), extrusion and molding is very easy. Its toughness is mainly determined by the ratio and usage of rubber components. The representative performance of impact resistance PS is: bending strength and tensile strength of 13.8-48.3MPa (different with the content of rubber and additives); elongation 10-60%; gloss 5-100%. The visual transparency ranges from excellent to poor, the shrinkage rate is about 0.006, and the thermal expansion coefficient is the same as that of transparent PS. Impact-resistant PS has no change in performance after γ-ray sterilization and irradiation, and has the same solvent resistance as transparent PS. The melt index of impact-resistant PS is 1-10g/min, and the Vicat softening point is 215°F. The commercial production of impact-resistant polystyrene with enhanced properties has broad market prospects. Some of the existing special grades include: ultra-high gloss grade, high transparency grade, abrasion resistance grade, environmental stress crack resistance (ESCR), high modulus grade, low gloss grade, and grades with low residual monomer styrene content .
The outstanding characteristics of impact-resistant polystyrene are easy processing, excellent dimensional stability, high impact strength and high rigidity. For HIPS only heat resistance. There are certain limits in oxygen permeability, ultraviolet light stability and oil resistance. Chemical and performance Impact-resistant polystyrene is made by dissolving polydiene rubber in styrene monomer before polymerization. Although the suspension polymerization method can be used to prepare HIPS, the bulk polymerization method is currently used in the industrial production of HIPS. In the bulk polymerization process, the styrene monomer/rubber/additive mixture passes through a series of reactors with a conversion rate of 70-90%. In the polymerization reaction, heating or adding an initiator is required to complete the reaction, and then heating in a vacuum to remove volatile residual monomers from the resin, and then pelletizing and selling.
The impact polystyrene performance test is divided into several levels according to its relative impact strength:
The impact strength of notched cantilever beams of medium impact resistance grade is generally 0.6-1./i;
The impact resistance of the high impact resistance grade is 1.5-2.5ftlb/in;
The impact strength of extremely high impact resistance is> 2./in
Some HIPS grades have an impact strength value of up to 6./in, but this resin is usually used in blended resins to improve the impact resistance of low-strength grade resins.
Other important performance testing matters needing attention of standard HIPS are as follows: bending strength 13.8-55.1MPa; tensile strength 13.8-41.4MPa; elongation at break 15-75%; density 1.035-1.04 g/ml; Vicat softening point 185- 220°F. 
The only industrially mixed HIPS alloy is its blend with polyphenylene ether. The heat resistance and toughness of this blend are outstanding, but the product price is much higher than that of HIPS alone.
The continuous development of polystyrene technology enables the production plant to produce grades with more outstanding performance than standard PS. Many properties of polystyrene cannot be achieved at the same time. If you want to improve the impact strength, you have to sacrifice gloss. Some new resins appearing at present have the glossiness of ABS and also have high toughness. Some grades, such as those that can withstand various oils and fats when packaging food, and chlorofluorocarbon (CFC) foaming agents when used in refrigerators, have also been developed. Flame-retardant grade (UL V-0 and UL 5-V), impact-resistant polystyrene has been produced and widely used in TV housings, business machines and electrical products. The processing operation of these resins is easier than many flame retardant engineering resins, and the price is lower.

PS generally has a head-to-tail structure, the main chain is a saturated carbon chain, and the side group is a conjugated benzene ring, which makes the molecular structure irregular, increases the rigidity of the molecule, and makes PS a non-crystalline linear polymer. Due to the presence of benzene ring, PS has a high Tg (80～105℃), so it is transparent and hard at room temperature. Due to the rigidity of the molecular chain, it is easy to cause stress cracking.
Polystyrene is colorless and transparent, can be freely colored, and its relative density is second only to PP and PE. It has excellent electrical properties, especially good high-frequency characteristics, second to F-4 and PPO. In addition, it is second only to methacrylic resin in terms of light stability, but its radiation resistance is the strongest among all plastics. The most important feature of polystyrene is that it has very good thermal stability and fluidity during melting, so it is easy to mold and process, especially injection molding is easy, and it is suitable for mass production. The molding shrinkage rate is small, and the dimensional stability of the molded product is also good.

Polystyrene has a glass transition temperature of 80 to 105°C, an amorphous density of 1.04 to 1.06 g/cm3, a crystal density of 1.11 to 1.12 g/cm3, a melting temperature of 240°C, and a resistivity of 1020 to 1022 ohm·cm. The thermal conductivity is 0.116W/(m·Kelvin) at 30℃. The usual polystyrene is an amorphous random polymer with excellent thermal insulation, insulation and transparency. The long-term use temperature is 0-70°C, but it is brittle and easy to crack at low temperature. In addition, there are isotactic and syndiotactic and atactic polystyrene. Identical polymers have high crystallinity, and syndiotactic polymers have partial crystallinity.