FLUOROPOLYMERS MOVE TO THE FOREFRONT
As previously stated, one of the original concerns with plastics was the many varieties to meet multiple design characteristics.
Biopharm engineers desired a more universal option. In other words, a polymer alternative to stainless steel. The industry
hit on the idea of a more defined and singular "contact layer" to meet the diversity required in SUS. This search for a common
contact material instinctively led its way to PVDF fluoropolymers (e.g., Kynar) for many reasons, as noted below (5).
PVDF is completely melt processable on conventional equipment allowing for its ability to be found in the complete range of
component forms required. This melt processability attribute extends itself to not only rigid parts (pipe, filter housings
and membranes, pumps) which use PVDF homopolymers, but also to parts favoring added flexibility (tubing, fittings, and film).
Copolymer PVDF resin helps attain the more flexible part designs while maintaining the purity and processability aspects.
Most importantly, the ease of melt processability allows for welding by various industry methods (6).
No processing aids or additives are required in PVDF fluoropolymer resin manufacturing, allowing for its compliance with USP
Classification VI. There are no animal derivatives in Kynar resins.
Fluoropolymers have low surface tension properties and as such do not have the propensity to attach to organic matter such
as proteins and lipids. This promotes increased manufacturing efficiencies as proteins do not stick to the bags or vessel
PVDF is unique among polymer materials as it is compatible to the various sterilization methods including gamma, autoclave
(steam), and chemical (EtO) (7). Gamma radiation is commonly used in disposables practices. Common industry gamma sterilization
levels are 25-30 KGy. Table II contains data that shows no change in properties even after doses twice the industry level
Table II: Properties of PVDF fluoropolymer (Kynar) before and after gamma sterilization at 50 kgy.
Multilayer adhesion technology
The ability to make multilayer film (bags) and tube structures was a final obstacle to overcome. As PVDF fluoropolymers have
the advantage of low surface tension, this same property can make it more difficult to adhere to complementing resins when
appropriate. This can often be the case in bag manufacturing. Multilayer bag structures and technology utilizing PVDF fluoropolymers
as the contact layer are now readily available due to the development of new extrusion designs. Such designs allow plastics
with additional barrier properties, such as EVOH, and lower cost softer resins, such as PE and copolyamides, to be incorportated
in outside layers.
The appropriate selection of polymers can offer long term advantages to metals in areas where cleaning agents are used. Plastic
materials are available that fully resist a broad range of chemicals and rusting or rouge is never a concern. PVDF can handle
steam, chlorinated disinfectants, oxidants and acidic chemicals at varied concentrations. PVDF belongs to the fluoropolymer
family of resins which contains the carbon-fluorine bond which is one of the strongest bonds in chemistry. The high energy
that is required to break this bond creates its unique chemical resistance across a broad range of pH values. PVDF components
are commonly used in applications where bleach, chlorine dioxide, chlorinated water, brominated water, ozone, peroxide, peracetic
acid, HCl, and alcohols are used in cleaning and bacterial control processes.