![\"Transparent](\"https:\/\/bastone-petrochem.com\/wp-content\/uploads\/2026\/05\/what-is-general-purpose-polystyrene-gpps-1.png\")
<\/figure>\n\n\n\nWhat Are GPPS’s Key Properties?<\/h2>\n\n\n\n
Four numbers govern whether a GPPS grade fits a part. The rest of the spec sheet is useful for finite-element work but irrelevant at point-of-quote.<\/p>\n\n\n\n
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- MFI (ASTM D1238, 200\u00b0C \/ 5 kg)<\/strong>: standard grades land at 5-10 g\/10min, high-flow at 20-34 g\/10min. MFI sets the molding window and the cycle-time math.<\/li>\n
- Vicat softening (ASTM D1525, Method A50)<\/strong>: 95-105\u00b0C across the family. Anything that sees autoclave, dishwasher, or hot-fill is out of scope, full stop.<\/li>\n
- Notched Izod<\/strong>: 15-25 J\/m. Fine for static parts on a shelf, marginal for parts that get dropped, wrong for parts under repeated impact.<\/li>\n
- Refractive index 1.59 \/ light transmission >88%<\/strong>: the optical signature that puts GPPS in cosmetic packaging, transparent cutlery, and clear-pack lids.<\/li>\n<\/ul>\n\n\n\n
Secondary specs typically include tensile strength at yield 40-55 MPa (ASTM D638), tensile modulus 3.0-3.3 GPa, flexural modulus 3.2-3.5 GPa, elongation at break 1-3%, and HDT 90\u00b0C at 1.82 MPa. These numbers confirm lot-to-lot consistency more than they drive selection.<\/p>\n\n\n\n
How GPPS Differs from HIPS at the Polymer Level<\/h2>\n\n\n\n
HIPS is GPPS with 5-10% polybutadiene rubber grafted onto the polystyrene backbone during polymerization. The rubber doesn’t dissolve into a homogeneous mixture \u2014 it forms discrete particles dispersed in a continuous polystyrene matrix.<\/p>\n\n\n\n
The same chain-architecture-to-spec-sheet logic governs the homopolymer-vs-copolymer split in polypropylene<\/a>, where adding a second monomer reshapes impact behavior the same way.<\/p>\n\n\n\n
Two consequences follow from the two-phase morphology. The rubber particles are larger than the wavelength of visible light, so they scatter incoming light \u2014 HIPS turns translucent while GPPS hits >88% light transmission. The particles also deform under stress and arrest crack propagation, pushing notched Izod from GPPS’s 15-25 J\/m up to roughly 50-100 J\/m in HIPS.<\/p>\n\n\n\n
The trade is binary at the polymer level. There is no “somewhat tougher GPPS” or “somewhat clearer HIPS” \u2014 these are structurally different materials. A part that needs both clarity and impact strength moves to PETG or polycarbonate, not a hybrid polystyrene.<\/p>\n\n\n\n
![\"Polymer](\"https:\/\/bastone-petrochem.com\/wp-content\/uploads\/2026\/05\/what-is-general-purpose-polystyrene-gpps-2.png\")
<\/figure>\n\n\n\nWhat GPPS Grades a Buyer Will See on a Quote<\/h2>\n\n\n\n
Asian commodity polystyrene producers<\/a> typically use a numeric grade-naming convention that clusters by MFI band. Once you know the convention, you can read a grade code on a quote and infer the application slot without opening the full COA.<\/p>\n\n\n\n
- Vicat softening (ASTM D1525, Method A50)<\/strong>: 95-105\u00b0C across the family. Anything that sees autoclave, dishwasher, or hot-fill is out of scope, full stop.<\/li>\n
![\"Procurement](\"https:\/\/bastone-petrochem.com\/wp-content\/uploads\/2026\/05\/what-is-general-purpose-polystyrene-gpps-3.png\")
<\/figure>\n\n\n\n![\"Clear](\"https:\/\/bastone-petrochem.com\/wp-content\/uploads\/2026\/05\/what-is-general-purpose-polystyrene-gpps-4.png\")
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