The Evolution from Fixed to Single-Use Systems - An overview of applications for disposable components and important property considerations. This article is part of a special issue on Single-Use Tech

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The Evolution from Fixed to Single-Use Systems
An overview of applications for disposable components and important property considerations. This article is part of a special issue on Single-Use Technologies.


BioPharm International Supplements
pp. s15-s20

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).

Processability

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).

High purity

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.

Cholesterol binding

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 walls.

Sterilizable


Table II: Properties of PVDF fluoropolymer (Kynar) before and after gamma sterilization at 50 kgy.
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 (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.

Chemical resistance

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.


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