It seems I am always being asked by customers, &#;What material is best for my job, PVC or PET?&#; I respond, &#;What is the function of your part?&#; Both of these materials have positive and negative aspects; depending on how you need the finished part to perform. I am going to pick a few key points that are important in the decision making process and highlight the good and bad of each material.
Let&#;s start with the most obvious factor: ENVIRONMENT. Both of these materials contain an oil base. However, the major difference is that PVC is comprised of 60% salt. Salt is a renewable resource. To me, that is a big plus for PVC. In years past, PVC has had a reputation of containing heavy metals. This was true. But today, heavy metals do not exist in PVC made in North America, and other reputable overseas suppliers. The BIG negative for PVC is the consumer recycling program in the US. Not many local municipalities accept the #3 plastic in their recycling bins. It has improved greatly over the past several years, but it is still in its infancy.
On the other hand, PET is probably the most recycled plastic that is used in the world. The water bottle that is sitting on your desk is PET. Soda bottles, food clamshells, retail packaging and cosmetic trays are just a few examples of items made from PET. And the recycling stream in the US is very well developed for this material and continues to grow every year.
WINNER: I believe PET has the edge because of the recycling stream that is in place.
Next factor is PRICE. Currently, PET is at its lowest price level in several years past. This is based on the price of oil and the fact that more companies are extruding this material. PVC pricing has been steady, and usually holds its price in the fluctuating oil market. That&#;s because it contains less oil than PET. Pound for pound, PET is about 20% less expensive than PVC. Another positive for PET is the price you receive for the scrap. PET scrap has a higher demand, leading to a higher scrap value. Just an FYI, the thermoforming process generates scrap. Scrap is the web that is left over after the part is picked from the sheet. We try to minimize this with mold placement, but it is something that cannot be avoided. At CMI we recycle 100% of all generated scrap material.
WINNER: PET, due to the fact that around 65% of the part price is material alone, no brainer.
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THERMOFORMING, I am referring to the ease of forming the part. Both materials have different characteristics. PVC runs slower than PET. PET likes to be formed with pressure. PET does not hold the heat as well as PVC, causing it to crystalize (turn white) if you overheat the sheet. With PVC, you can build a simpler tool that does not need a pressure box (additional tooling cost if your tool size is custom). Also, PVC is easier to form, making debugging time shorter and less costly. If you have a large run that needs to run very fast, PET is the answer. PVC also tends to work better with taller parts as it tends to be easier to distribute material.
WINNER: Toss Up, depends on the size of the part, the job, and the budget for the tool.
SIDE NOTE about PET: When we talk about PET (Polyethylene terephthalate) we are talking about virgin material. When we see R-PET, the &#;R&#; tells us it has recycled material in the formula. Earlier, I stated that we recycle all of the scrap we generate at CMI. Most of that goes back into creating sheet for similar jobs. But that source is not enough to fill the pipeline for R-PET, so most of the material comes from water/soda bottles. This PET was originally made for blow molding: the process used to make bottles. It has different properties than the thermoforming grade of the same material. But the larger factor that affects R-PET is the heat history. When you recycle PET over and over, it retains a heat history from each occurrence. What this does is make the R-PET sheet have less integrity than virgin PET or even PVC. When you buy R-PET sheet, you have no idea how many times it has been recycled. If it has been recycled several times, it may be difficult to form the parts. Also, the material may crystalize very easily, and your part may be very brittle and weak. These are all facts about PET, but, if your sheet supplier is reputable, you can be sure that they are buying quality R-PET flake and giving you a good material. In saying all of that, PVC and R-PVC may be a better choice if you need your part to be structurally stable.
A FEW MORE POINTS: Sealing (R/F sealing) PVC is easier than PET. You can seal PET, but it requires different tooling than PVC. It is also harder to get a complete perimeter seal with PET. When talking about the clarity of the material, both are similar. If you are buying a recycled grade of either material, you may receive material that has a slight tint. Tints could be blue, green, and I have had R-PET with a very slight yellow tint. It all depends on the feed stock the extruder is using.
WINNER: on these points, PVC takes it.
Overall, both materials are very good for thermoforming, depending on your needs. I feel that the material that comes out on top is PET because so many large companies (and Europe) have directives to avoid PVC. There are other clear material alternatives such as PET-G: a good material that has the characteristics of PVC, yet is a &#;#1&#; in the recycling stream. Due to its higher cost, it may not be an option compared to the other two materials.
CMI can work with you to help you decide what material is best for your project. Find us at www.cmiplastics.com or me at . I hope you are able to use the information in the future to determine the right material for your project.
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