Polypropylene

What gives polypropylene its properties

PP is produced by polymerising propylene. Commercial grades are typically semi-crystalline: their molecular structure contains both ordered and less ordered regions. Polymer structure, comonomer content and additives influence the balance between rigidity, toughness, clarity and thermal behaviour.

Low density makes PP attractive where component weight and material use matter. Many grades offer useful resistance to aqueous chemicals and moisture, while suitable grades can withstand repeated flexing in a correctly designed living hinge. Chemical compatibility still depends on the actual substance, temperature, exposure time and mechanical stress.

PP also has limitations that should shape the design. Impact performance at low temperatures varies considerably between grades. Outdoor use requires appropriate stabilisation, and printing or bonding may require surface treatment. A melting temperature or a single heat-deflection result does not establish the safe continuous operating temperature of a finished part.

Homopolymer, random copolymer and impact copolymer

PP homopolymer. Main selection priorities: Stiffness, low weight and efficient processing; specialised grades address film, fibre or high crystallinity requirements. Typical applications: Rigid packaging, housewares, woven tapes, fibres and oriented film.

PP random copolymer. Main selection priorities: Clarity and a useful balance of flexibility and toughness; performance depends on comonomer content and clarification. Typical applications: Transparent containers, lids, selected film layers and medical components.

PP impact copolymer. Main selection priorities: Improved toughness through a dispersed rubber phase; balance impact resistance against stiffness and appearance. Typical applications: Transport packaging, durable mouldings and automotive components.

An impact copolymer is not a random copolymer with a different label. Their structures and property balances differ. Likewise, a high-crystallinity grade describes a particular property profile, while a metallocene grade describes the catalyst technology used to control polymer structure. These terms answer different questions and should not be treated as interchangeable product categories.

How polypropylene is processed

Injection moulding converts suitable PP grades into thin-wall packaging, closures, household articles and technical components. Flow behaviour affects mould filling, but the highest melt flow rate is not automatically the best choice. Part geometry, stiffness, impact requirements, shrinkage and dimensional stability also matter.

Film extrusion produces cast polypropylene film, while biaxial orientation produces BOPP film with a different combination of strength, stiffness and optical behaviour. Film grades must be matched to the line, stretching conditions where applicable, sealing requirements and downstream operations such as printing or metallisation.

Fibre, spunbond and meltblown processes require their own viscosity and processing profiles. A grade suitable for injection moulding cannot be assumed to be suitable for fine fibres. PP can also be extruded into sheet for thermoforming, with material selection governed by the forming process and the finished article.

Matching PP to the application

For rigid packaging, define the balance between wall thickness, stacking strength, impact performance and appearance. A clear container may favour a clarified random copolymer, whereas a tough transport container may call for an impact copolymer. Thin-wall packaging adds a demanding mould-filling requirement.

For automotive and durable products, assess impact performance at the intended service temperature alongside stiffness and dimensional requirements. Surface appearance, chemical exposure and the assembly method may be as important as the headline mechanical properties.

For healthcare components, resin selection includes documentation and qualification requirements as well as physical performance. Sterilisation compatibility must be established for the selected grade and the complete sterilisation process; it cannot be inferred from the PP name alone.

Velogy polypropylene supplied by Genesis Polymers Europe

KeyForm PP covers a broad range of established applications. Examples include KeyForm P1340 for rigid mouldings, KeyForm P1640 for high-flow injection moulding, and KeyForm P0702 for BOPP film applications including metallisation.

AdvyForm PP addresses more demanding performance targets. AdvyForm P1330 provides a high-crystallinity homopolymer option, while AdvyForm M1640 is a metallocene PP option for applications such as transparent thin-wall mouldings. AdvyForm R1002 and R1052 extend the range of options for cast film; the choice also depends on the required additive package.

CertyForm PP focuses on healthcare applications. Examples include CertyForm R1320 for two-piece syringes and CertyForm R1330 for three-piece syringes. The finished device and its manufacturing process still require application-specific qualification.

Explore the KeyForm, AdvyForm and CertyForm brand pages for more detailed grade examples. Brand membership does not replace the technical data sheet: properties and processing recommendations must be checked for the individual grade.

A short history of polypropylene

Catalyst developments in the 1950s made commercially useful polypropylene possible. Subsequent advances in polymerisation, copolymer design and additives expanded its use from everyday goods into specialised packaging, transport and healthcare applications.