Hello and welcome to this blog post in which I discuss the differences and similarities of PVC and PVDC, as well as the unique barrier properties of PVDC.
Re-cap: what is PVC?
Poly(vinyl chloride) is an amorphous thermoplastic polymer consisting of carbon (C), hydrogen (H) and chlorine (Cl) and PVC is, after polyolefins, the second largest plastics material group. Since the molar weight of this polymer contains 56.7% of chlorine [1], it uses less petroleum and gas feedstock for its production in comparison to other polyolefins. This elevated content of chlorine also provides PVC with flame-retarding properties. As a result, PVC holds the lead in civil- and construction engineering applications, such as isolations and floorings. Apart from the construction sector, PVC plays an important role in medical device applications, where it ranks right after the Polyolefins in overall usage. A blog post on detailed applications using PVC in medical device applications can be found here.
What Is Polyvinylidene Chloride (PVDC)?
PVDC fulfils not the classic definition of high heat/performance polymers (UL 746B - polymers need to withstand a continuous use temperature of 150°C for 100,000 hours), however we can classify it as a special polymer, based on its unique set of properties.
PVDC, chemically defined as 1,1-Dichloroethene, has a temperature usage range from -20°C up to +100°C (from 160°C on chemical-thermal degradation starts, resulting in hydrogen chloride). The additional Chlorine results in a semi-crystalline morphology, whereas PVC is an amorphous polymer.
What is the difference between PVDC and PVC?
Figure 1 shows the chemical structure of PVC and PVDC. It can be seen that PVDC contains double the amount of chlorine compared to PVC. The combination of symmetric Chlorine leads to a high barrier towards oxygen and water vapor as well as superior flame retardancy performance. Figure 1 also contains the oxygen permeability of PVOH, EVOH, PVDC, and R-PVC. PVOH and EVOH perform slightly better than PVDC, however if you combine it with the water vapor chart, things look differently. PVDC has a low water vapor permeability compared to PVOH and EVOH. This allows you to have a material which has excellent oxygen and water vapor resistance which can be used for several interesting applications.
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| Figure 1: Chemical structure of PVC and PVDC, together with oxygen and water vapor permeability [5]. |
PVDC applications
PVDC is mainly used as film for packaging applications and as waterborne high-barrier resin dispersion which allows coating of textiles, paper, and plastics.
For packaging, the combination of oxygen and water vapor barrier play a role for fresh and processed meat packaging, together with dry fruit, seafood and vegetable packaging.
In the field of medical packaging, PVDC is used for pouching systems.
Also wine bottle caps use PVDC as a barrier layer. The well known Stelvin wine caps use a Saranex™ liner based on a PVDC [7].
Conclusions
To summarise, PVDC is a high barrier polymer with outstanding gas barrier and water vapor properties. This unique combination of properties makes it an optimal material choice during your material selection journey for advanced packaging and medical film solutions. Apart from PVDC, PARA (MXD6) has also interesting barrier properties which we discuss in the post here.
Thanks for reading and #findoutaboutplastics
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Literature:
[1] W. Kaiser: Kunststoffchemie für Ingenieure: Von der Synthese bis zur Anwendung, Carl Hanser (2011)
[2] https://www.findoutaboutplastics.com/2015/02/pvc-not-always-in-best-spot-but-still.html
[3] https://www.findoutaboutplastics.com/2017/03/my-top-5-commodity-plastics-for-medical_23.html
[4] https://us.metoree.com/categories/5347/
[5] https://www.syensqo.com/en/brands/ixan-pvdc/faq
[6] https://www.amcor.com/stelvin
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