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Brentwood Plastics blog

EVA and PEVA - be specific

Posted by Joel Longstreth on Tue, Nov 08, 2011 @ 12:25 PM

EVA and PEVA are both acronyms for Ethylene Vinyl Acetate.  Somehow the P for polyethylene was added to create the acronym "PEVA."

To make EVA copolymer, Vinyl Acetate Monomer or "VAM" is copolymerized, or conjoined with Ethylene monomer to make Ethylene Vinyl Acetate. 

EVA copolymer is made in varying percentages from 2% EVA, 4% EVA, 6% EVA, 8 % EVA up to about 28 % EVA for blown film.  If you order simply "EVA" it is too broad and not specific enough.
The percentage of EVA is critical because the greater the EVA component, the lower the melting point.  This affects the EVA film performance properties.  If you are RF welding, the more EVA is needed for response to RF frequencies.  For low melt / total batch inclusion, the amount of EVA must be known to match with the desired melting point.  EVA is popular for solar photovoltaic pv cell encapsulation, yet EVA film suppliers do not specify the percent of EVA in the film for solar panel manufacturers.

When ordering EVA film, be sure to specify the amount of EVA for consistent performance.

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Topics: EVA sheet solar, EVA film, solar panel manufacturers, PEVA film, PEVA, EVA film supplier

Metallocene VS EVA

Posted by sam Longstreth on Tue, Jun 21, 2011 @ 11:33 AM

Ethyl Vinyl Acetate (EVA) is a living dinosaur.  It should be extinct but it isn't.  In it's raw state EVA has the consistency of clear rubber.  It smells like vinegar. When added to homopolymer polyethylene in samll percentages (1 to 3%) it can enhance the clarity and sealability of a film.  When added in higher percentages (4 to 6%) it further enhances sealabilty and increases the films's cold stress crack resistance.  At the 4 to 6% loading the optics of the film decrease due to the high amounts of antiblock needed to prevent the film from sticking to itself.  Even higher loadings of EVA are still used for very cold applications and in situations where there is a large amount of contaminate in the seal area.   We stock it because people still buy it even though they would be better off using a very low density metallocene.  

We understand resistance to change but we don't like it.  Metallocenes have better optics, better physicals, a lower heat seal initiation temperature, better cold temperature stress crack resitance, less taste transfer, less expensive and offers a better opportunity for downgauging than EVA's.  When we ask people why they want EVA they say, "Its what we've always used and it is written in the spec.".  Why laminators still call out EVA in their specifications for sealant webs is beyond reason.  In some radio frequency welding applications EVA may be a better choice than metallocenes but we have several brave customers who have made the transition away from EVA to metallocene for RF welding applications.  IF you are still using EVA give us a call and we can show you how metallocenes can improve your life. 

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Topics: metallocene, EVA, PEVA

PEVA film is not the only PVC substitute

Posted by Joel Longstreth on Wed, May 18, 2011 @ 02:37 PM

not PVC shower curtainPEVA materials are not the only PVC substitute film.

PEVA film is a popular substitute where PVC has been banned mainly because it is what is known as a "polar" molecule.  The properties of polyethylene film copolymer EVA also known as PEVA material most closely mimic the polar nature of PVC.  This makes "PEVA" the path of least resistance when substituting for PVC. 

PEVA shower curtains are a ubiquitous PEVA film success story.  It is interesting to note that the retail price of a PEVA shower curtain is about triple the cost of a PVC shower curtain.  The cost to manufacture is identical for both PVC shower curtains and PEVA shower curtains.  The claims of "Eco Friendly" and biodegradable are unabashed greenwashing claims know politely as "son of fibbing" or outright lies depending on who is defining the greenwashing sin.

Not all PEVA's are created equal.  PEVA is short for "Polyethylene Ethylene Vinyl Acetate" which is a copolymer of ethylene and vinyl acetate. The copolymer is made by the resin producer in varying percentages, not added by the blown film manufacturer.  Therefore it is essential to specify the percentage of EVA copolymer in the PEVA material.

New metallocene catalyst polyethylene films emulate the "hand" of calendared PVC.  Metallocenes have proven to be very clean in biotoxicity tests in medical applications requiring prolonged and direct skin contact.  While RF welding metallocene requires a learning curve and a modified "buffer", metallocenes are readily heat sealable.  Custom shapes can be achieved by a heated seal which is a heated die rule.

An additional side benefit to both PEVA and metallocenes used where PVC is banned is they are considered "burnable" by European standards. 

describe the image

A new category of polymers which we'll call thermoplastic olefins, or TPO's for short open up some exciting possibitlies such as digital printable custom shower curtains and wallcoverings

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Topics: PEVA, PEVA material, PEVA shower curtains

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