Classification by Polymerization Type
This is the most basic and essential classification method, stemming from differences in polymerization processes and molecular chain structures, which directly determine the material’s fundamental performance framework.
Polypropylene is primarily classified into three categories, homopolymer polypropylene, random copolymer polypropylene, and impact copolymer polypropylene.
Homopolymer Polypropylene PPH
Made from the polymerization of pure propylene monomers, it has a highly regular molecular chain structure and the highest crystallinity, reaching 60-70%.
>> Performance Characteristics
High rigidity and hardness. It exhibits the highest tensile strength and flexural modulus of the three types.
Excellent heat resistance. Its heat deflection temperature (HDT) is high, typically exceeding 100°C, making it suitable for applications requiring high-temperature resistance.
Good chemical stability. It exhibits excellent resistance to most acid, alkali, and salt solutions.
Disadvantages. Poor low-temperature impact resistance and average creep resistance. Products can easily crack at low temperatures or under impact.
>> Main Applications
Microwaveable lunch boxes, household appliance components (such as washing machine drums and electric iron casings), water pipes, woven bags, transparent water cups, disposable syringe barrels, industrial yarn, and sheet materials.
Random Copolymer Polypropylene (PPR)
A small amount of ethylene monomer is randomly inserted into the propylene polymer chain. The introduction of ethylene monomer disrupts the regularity of the molecular chain.
>> Performance Characteristics
High transparency and gloss. Due to its reduced crystallinity, its transparency is far superior to homopolymer PP and comparable to PS and PET.
High toughness. It has better impact resistance and ductility than homopolymer PP, especially at low temperatures.
Good chemical resistance. It maintains the inherent chemical stability of PP.
Disadvantages. Its rigidity, hardness, and heat resistance are somewhat lower than those of homopolymer PP.
>> Main Applications
Transparent packaging (such as premium food containers, storage boxes, and medical device packaging), transparent bottle caps, disposable syringe plungers, tubing (especially hot and cold water pipes, PPR pipes), and films, among other applications requiring transparency and toughness.
Block Copolymer Polypropylene (PPB)
Usually produced using a multi-stage polymerization process, an ethylene propylene rubber phase is in situ generated and dispersed within a PP homopolymer matrix. The rubber phase acts as a toughening agent within the PP matrix.
>> Performance Characteristics
Extremely high impact strength. This is its core advantage, particularly low-temperature impact resistance, which far exceeds that of homopolymer and random copolymer PP.
High toughness. Maintains excellent toughness even at low temperatures, preventing brittle fracture.
Disadvantages. Rigidity, hardness, and heat resistance are significantly reduced due to the addition of the rubber phase.
>> Main Applications
Automotive (bumpers, side skirts, interior panels, battery pack casings), large industrial parts (logistics pallets, transfer boxes, forklift pallets), home appliances (washing machine drain pans, vacuum cleaner housings), strollers, luggage, and other components subject to high impact loads.
Classification by Modification Method
Base polymers typically require physical or chemical modification to meet the stringent performance requirements of specific applications.
Filler-Reinforced
Improve rigidity, heat resistance, and dimensional stability, while reducing shrinkage and cost.
Common Fillers:
Talc. The most commonly used reinforcing filler. Significantly improves rigidity, heat resistance, and surface hardness.
Calcium Carbonate CaCO3. Mainly used to reduce cost and improve rigidity to a certain extent, but its reinforcing effect is not as good as talc.
Glass Fiber. It is an excellent reinforcement. Significantly improves strength, rigidity, heat resistance, and creep resistance, but can result in anisotropic shrinkage and poor surface appearance.
Toughened and Modified Type
Specifically designed to improve impact toughness.
Common toughening agents: POE (polyolefin elastomer), EPDM (ethylene propylene diene monomer), etc.
Applications: Commonly used in homopolymer PP to create ultra-high-impact grades, or to improve the toughness of other plastics.
Functionalized Modified Type
Flame-Retardant Polypropylene (FRPP). Flame retardants such as bromine, phosphorus, nitrogen, or inorganic hydroxides are added to achieve UL94 V-0, V-1, or V-2 flame retardancy ratings. Used in electronic and electrical components (such as sockets, circuit breaker housings, and charger housings).
Antistatic/Conductive Polypropylene. Carbon black, metal fibers, or permanent antistatic agents are added. Used in carrier tapes, trays, and explosion-proof enclosures for packaging precision electronic components.
Weather-Resistant Polypropylene. High-efficiency UV inhibitors and antioxidants are added to prevent aging, chalking, and performance degradation caused by sunlight. Used in automotive exteriors, outdoor furniture, and other applications.
Transparent Nucleated Polypropylene. By adding nucleating agents such as sorbitol, the spherulite size is reduced, significantly improving the transparency and gloss of homopolymer PP.
Classification by Processing Application
PP resins are designed into grades with different properties depending on the downstream product processing, with melt flow rate (MFR) being the most critical indicator.
Injection Molding Grade Polypropylene
High MFR (20-100+ g/10min) is used for thin-walled products and complex structural parts.
Medium MFR (5-20 g/10min) is used for general-purpose products.
Low MFR (1-5 g/10min) is used for high-impact, thick-walled products.
Extrusion Grade Polypropylene
A low MFR (0.1-2.0 g/10min) is typically required to ensure melt strength and prevent sag.
>> Applications:
Extruded sheet/plate. Used for thermoforming into trays, billboards, etc.
Extruded fiber. Ultra-high MFR (>30) is used for woven bags, carpet backing, and nonwoven fabrics.
Extruded pipe. Low MFR, used for water supply and drainage pipes.
Blow molding-grade polypropylene
Requires a medium-to-low MFR (0.5-2.0 g/10min) and extremely high melt strength to ensure parison quality and prevent sagging.
>> Applications: Bottle hollow containers, automotive air ducts, etc.
Thermoforming-grade polypropylene
Usually used as extruded sheet, the raw material has high melt strength requirements.
>> Applications: Transparent fast food boxes, milk tea cups, etc.
Fiber-grade polypropylene
Fiber-grade polypropylene typically has a very high MFR, ranging from 25-45 g/10min. This means it has excellent flowability in the molten state and can be easily drawn into extremely fine fibers.
Spunbond meltblown-grade polypropylene
With an ultra-high MFR (>1000 g/10min), it is specifically used in the production of nonwoven fabrics and is a core material for masks, protective clothing, and diapers.