Plastic Knowledge should know

General-purpose plastics

Primarily includes polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), ABS (acrylonitrile butadiene styrene), polymethyl methacrylate (PMMA), and amino plastics. These account for over 90% of total plastic production, hence they are also known as commodity plastics.

Engineering Plastics

These possess superior mechanical properties, high-temperature resistance, and corrosion resistance, making them suitable as structural materials. They exhibit excellent overall performance, maintaining these characteristics over extended periods and across broad temperature ranges. They can withstand mechanical stress and endure prolonged exposure to demanding chemical and physical environments. Engineering plastics are further categorized into general-purpose engineering plastics and specialty engineering plastics.

General-purpose engineering plastics

primarily include: polyamide (PA), polycarbonate (PC), polyoxymethylene (POM), modified polyphenylene oxide (PPO), and thermoplastic polyesters (PBT/PET);

Specialty Engineering Plastics

These are engineering plastics with heat resistance exceeding 150°C. Primary varieties include polyimide (PI), polyphenylene sulfide (PPS), polysulfones (PSF or PSU), aromatic polyamides, polyarylate (PAR), polyphenylene ester, polyaryletherketone (PEEK), liquid crystal polymers (LCP), and fluoropolymers.

Crystallinity (Plastics)

Crystallization refers to the regular arrangement of molecules, forming a crystalline structure upon cooling. The crystalline structure of typical plastics consists of aggregates formed by numerous linear, elongated polymer chains. The degree to which molecules align in a regular pattern is termed crystallinity. Since only individual molecules exhibit orderly arrangement, crystalline resins are actually only partially crystalline. The proportion of crystalline regions constitutes the crystallinity.

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Figure: Overview of Plastic Crystallinity

Amorphous Plastics

These are plastics where molecular shapes and arrangements lack crystalline structure, exhibiting disordered states (e.g., ABS, PC, PVC, PS, PMMA, EVA, AS). Non-crystalline plastics display identical mechanical properties in all directions (isotropy).

Thermoplastics

These plastics can be repeatedly softened by heating and hardened by cooling within a specific temperature range (e.g., ABS, PP, POM, PC, PS, PVC, PA, PMMA, etc.). They are recyclable.

Thermosetting Plastics

These are plastics that become non-meltable when heated and lose plasticity upon subsequent heating, making them non-recyclable (e.g., phenolic resin, epoxy resin, amino resin, polyurethane, expanded polystyrene).

Transparent Plastics

Generally categorized into transparent, translucent, and opaque plastics. Plastics with light transmittance exceeding 88% are termed transparent (e.g., PMMA, PS, PC, Z-polyester, etc.). Common translucent plastics include: PP, PVC, PE, AS, PET, MBS, PSF, etc. Opaque plastics primarily consist of POM, PA, ABS, HIPS, PPO, etc.

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Image: Transparent PC Granules

Rigid Plastics, Semi-Rigid Plastics, and Flexible Plastics

Common rigid plastics include: ABS, POM, PS, PMMA, PC, PET, PBT, PPO, etc.

Semi-rigid plastics include: PP, PE, PA, PVC, etc.

Flexible plastics include: PVC (soft), K-resin (BS), TPE, TPR, EVA, TPU, etc.

Plastic hardness serves as a fundamental criterion for material differentiation!

Classification by Chemical Structure

A. Polyolefins (e.g., LDPE, MDPE, HDPE, LLDPE, UHMWPE, PP, etc.)

B. Polystyrenes (e.g., PS, AS, BS, ABS, MBS, HIPS, etc.)

C. Polyamides (e.g., PA6, PA66, PA610, PA10T, PA612, etc.)

D. Polyether-based (e.g., PEEK, POM, PPS, PPO, etc.)

E. Polyester-based (e.g., PBT, PET, etc.)

F. Acrylate-based (e.g., PMMA)