Characteristics and processing conditions of medical PP plastics

2021-03-23 14:31:40 admin

PP material characteristics and processing conditions during injection molding of medical plastic parts

Medical PP plastics have higher transparency, better barrier properties and radiation resistance, making them widely used in medical equipment and packaging industries. Non-PVC material with PP plastic as the main body is a substitute for the widely used PVC material.

Characteristics of medical PP plastic

PP plastic is colorless, tasteless and non-toxic. It looks like polyethylene, but it is more transparent and lighter than polyethylene. PP is a kind of thermoplastic with excellent performance. It has the advantages of small specific gravity (0.9g/cm3), non-toxicity, easy processing, impact resistance and flexural resistance.

The main properties of medical PP plastic

High temperature disinfection:

PP plastic is a semi-crystalline material with high melting point, good heat resistance, and can be sterilized at a temperature above 100°C. The yield strength, tensile strength, compressive strength, hardness and elasticity are higher than those of polyethylene (PE).

Low temperature resistance and impact resistance:

Homo-PP is more brittle, and random copolymer PP synthesized with ethylene has better toughness and stronger impact strength. For products usually used under low temperature conditions, it is necessary to use copolymer PP as much as possible, or add thermoplastic rubber to modify PP to increase its flexibility and low temperature impact resistance.

Non-PVC large infusion bag is made of copolymerized PP and elastomer blended modified materials.


It is very easy to depolymerize and age under the action of oxygen, heat and light, so anti-aging agent must be added. PP products are not easy to bond, and need to be processed before bonding, and special adhesives must be used. The cyclohexanone used by the equipment factory cannot meet the requirements. The colorability is poor, the shrinkage rate is large (usually 1.6-2.5%), the burning resistance is poor, and it is easy to catch fire. PP is a non-polar material and has a low adsorption capacity for drugs.

Processing conditions

Processing technology:

It can be injection molded, extruded, blow molded or made into a film. PP film is usually welded into bags by heat sealing method, and its processing technology is more complicated than that of high-frequency welding PVC bags. Non-PVC large infusion bags are produced using fully automatic equipment to ensure stable process and reliable quality.

Drying treatment: low water absorption, no drying treatment is required.

Melting temperature: 220-270℃, be careful not to exceed 275℃. Mold temperature: 40-80℃, 50℃ is recommended.

Injection pressure: up to 1800bar.

Injection speed: The use of high-speed injection can reduce the internal pressure to a minimum. If there are defects on the surface of the product, low-speed injection at a higher temperature should be used.

Runner and gate:

For cold runners, the typical runner diameter range is 4-7mm. It is recommended to use a circular injection port and runner. All types of gates can be used. The typical gate diameter ranges from 1 to 1.5mm, but gates as small as 0.7mm can also be used. For edge gates, the small gate depth should be half the wall thickness; the smallest gate width should be at least twice the wall thickness. PP material can use hot runner system.