PP-H (Polypropylene)

Polypropylene: Homopolymers and Copolymers.

There are two types of polypropylene: homopolymers (PP-H) and copolymers (PP-C).

PP-H is completely polymerised from propylene and covers the temperature range from 0°C to +100°C. In addition, compared to PP-C, it offers high strength to weight ratio, it is stiffer and stronger, good chemical resistance and weldability, good processability, good impact resistance, food contact acceptable and it is suitable for corrosion resistant structures.

PP-C features a chemical combination of propylene and ethylene monomers, which increases the material’s impact strength at low temperature. PP-C covers a temperature range from -20°C to +80°C In addition, compared to PP-H, it is less rigid, softer but has better impact strength; tougher and more durable. It also offers a better stress crack resistance and low temperature toughness. It is not preferable for food contact applications.

At D.H. Lamina we offer and we machine PP-H.

PP main properties and characteristics.

Polypropylene is one of the lightest polymers among all commodity plastics, for this reason it is suitable for lightweight or weight saving application. Its density is only 0,9 g/cm3 circa.

Through its great characteristics we underline a great chemical resistance. It resists to diluted and concentrated acids, alcohols, bases, aldehydes, esters, hydrocarbons and ketone. It is weaker in contact with aromatic, halogenated hydrocarbons and oxidizing agents.

Even if it is one of the cheapest material, PP offers anyway good mechanical and electrical properties even at middle-high temperatures, in humid conditions and when submerged into water. It assures a good resistance to environmental stress cracking and steam sterilisation.

Polypropylene is an high flammable plastic, its melting point is around 160 – 165°C.

Although these good characteristics, PP-H is poor resistance to UV, impact and scratches. Polypropylene homopolymer embrittles below -20°C, it has a low upper service temperature, 90-120°C. It could be attacked by highly oxidizing acids, swell rapidly in chlorinated solvents and aromatics. In additions to that, heat-aging stability is adversely affected by contact with metals and it has a poor paint adhesion.

Polypropylene or Polyethylene?

Both of these materials belong to olefin polymers and their characteristics are very similar. Anyway, there are few characteristics which differ from one to another.

For example, Polypropylene (made of propylene monomer), it can be produced optically clear, it is lighter in weight, it exhibits a high resistance to cracking, acids, organic solvents and electrolytes. Moreover it has high melting point, good dielectric properties and it is more rigid than polyethylene.

On the opposite side, Polyethylene (made of ethylene monomer) can only be made white translucent and its physical properties allow it to stand up better in cold temperatures. In addition to that it is a good electrical insulator.

Additives and miscellaneous information

Polypropylene is a basic material, but it can be improved with different additives to increase its characteristics. From extrusion, not all variants are usually available, but we can offer finished components made of ELECTROCONDUCTIVE POLYPROPYLENE (PP-H ELS). PP-H ELS is an electrically conductive homopolymer polypropylene with flame-retardant additive. This material is treated with electrically conductive particles which discharge the static. PP-H ELS has low surface resistivity and is ideal for use in potentially explosive atmospheres.

PP-H is usually available in GREY RAL 7032 and BLACK.

It is a non-toxic material, in fact it can be certified EU 10/2011 and FDA.

Polypropylene in few words.

Special properties:

• Excellent chemical resistance;
• Low density;
• High purity;
• Very low moisture absorption;
• High thermal expansion;
• No stress crack formation;
• Low toughness in minus temperature range, sensitive to impact.

Used in:

• Packaging;
• Chemical Industry;
• Pumps & Valves;
• Automotive;
• Food Industry.

Applications:

• Fittings;
• Valves;
• Tubes;
• Gaskets;
• Components for pumps.