Key Facts About Polypropylene

Choosing the right plastic for your application can be confusing, particularly if you are new to the industry. We gave a quick overview of the polymers that Impact extrudes, touching on their general characteristics and typical uses.
In this next blog post, we narrow our focus to discuss one of the materials we extrude in greater detail – polypropylene. If you couldn’t tell from our other blog posts, we at Impact Plastics love PP for a variety of reasons. PP is an economical material that offers an outstanding combination of physical, chemical, thermal and sustainable attributes. Continue reading to learn 7 key facts about PP plastic:

PP comes in several different grades:

One of the wonderful, but confusing, things about PP is that there are several different grades of the same polymer and no two resins behave alike. While this may seem like complicated, the positive is that this gives us the opportunity to tailor the plastic sheet formulation to a customers exact application.

The three main grades of PP are homopolymer, random copolymer, and impact (or block) copolymer. Homopolymer PP is the most rigid grade of the three. Random copolymer PP resins contain ethylene, which results in improved impact strength and a softer feel compared to homopolymers. Similarly, block Copolymer PP resins contain ethylene, but to a greater degree, resulting in a tougher material with excellent impact strength even at low temperatures.  Impact Plastics produces polypropylene sheet in all three grades.

PP is a semi-crystalline polymer:
PP is a semi-crystalline polymer which means that the plastic exhibits organized and tightly packed molecular chains. The areas of crystallinity are called spherulites and can vary in shape and size with amorphous areas existing between the crystalline areas. The degree of crystallinity affects many characteristics of the polymer. The semi-crystalline nature of PP is what gives this material it’s hazy appearance in its natural state.

PP has a low weight and high density:
PP has the lightest weight of all the polymers and it is also the polymer with the lowest density. What this means is that by making the switch, buyers of polypropylene sheet can experience up to a 30% yield over polymers like PET and PVC resulting in more parts for the same amount of material. This increased polymer yeild in turn translates to a cost savings that is sent right back to the bottom line. In addition, because of the lightweight nature of this plastic, this translates to less solid waste by weight, resulting in a more sustainable solution.

1. When working in the food packaging industry, oxygen and moisture barrier properties are critical specifications. When it comes to moisture, PP possesses inherent moisture barrier properties. PP has a Moisture Vapor Transmission Rate (MVTR) of 0.5 (g-mil.100 in. 2/24hr.). MVTR is a measure of the passage of gaseous H2O through a barrier – the lower the rate, the longer the package protects its contents from moisture and ensures that moisture of the product remains the same. PP has the same MVTR as HDPE. As a basis of comparison, PS has an MVTR of 10.0, PET has an MVTR of 2.0, and PVC an MVTR of 3.0. This means, not only does the material keep unwanted moisture out, but it keeps moisture in, making it an ideal for food certain packaging applications, such as bakery applications, where it is important for the food to retain it’s moisture content.
   
   When it comes to oxygen barrier properties, PP is not traditionally seen as an effective oxygen barrier, however Impact Plastics has recently developed a proprietary formulation with superior oxygen barrier properties. 

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