PVDF and PVDF Copolymers PVDF and PVDF: The Versatile and Viable Material Choice
The use of Kynar Polyvinylidene Fluoride (PVDF) is gaining traction across industries where chemicals are extensively used, thanks to the special attributes of this material that have proven its viability in various applications.
Since the construction of the first Kynar PVDF commercial plant at Calvert City, Kentucky, USA, in 1965, this product has been extensively used for various applications in the chemical industry. Initially, the applications for PVDF centered on the excellent chemical resistance to chlorine and chlorinated solvents, bromine, hot acids and several combinations of chemicals for waste handling. Users in these chemical arenas soon discovered other special properties of PVDF that were not universally associated with all plastics. It offered high abrasion resistance similar to ultra-high molecular weight (UHMW) polyethylene and nylon, and high tensile strength at elevated temperatures, which set it apart from commodity plastics and other fluoropolymers.
Moreover, PVDF exhibited the ability to withstand high doses of radiation in service – which made it superior to almost any known polymer – along with excellent flame resistance, superior sunlight resistance (UV) and overall weathering durability.
Plastic can be a High End Product
Simply put, PVDF is a high-end plastic and can serve as an ideal solution to equipment designers and engineers who prefer a thermoplastic material over metal components for chemical-related applications, but have not yet found a material that meets all their needs economically.
The advantages of PVDF or PVDF copolymers in various areas are listed here in an effort to make it easy to understand why and where these could be used in specific chemical handling applications.
Pulp and Paper Bleaching
The pulp and paper industry commonly utilizes chlorine-based technology for bleaching operations. Chlorine is very aggressive to metals and causes the equipment to rust and corrode quickly.
Additionally, chlorine and chlorinated compounds are aggressive to many polymers, ultimately leading to corrosion-induced stress cracking. PVDF is not attacked by chlorine to a great extent, and is often used for long-term handling of chlorinated chemicals. In bleach applications where the chlorinated compound is also blended with a caustic solution that increases pH level, PVDF copolymers are preferred because the softer and more flexible nature of this technology offers better overall resistance to any potential cracking over time.
Metals Preparation and Mining
In the metals industry, various acids that include strong ones like hydrofluoric, hydrochloric, sulfuric, nitric, chromic, etc., are used to clean, treat/prepare or separate the final product. The concentrations of these chemicals can vary throughout the process; temperatures tend to be elevated; and mixtures of acids are common. This combination of variables makes it difficult to find one material to meet the needs for handling the process and waste chemicals.
PVDF and PVDF copolymers extend the temperature limits of the equipment and ensure protection from upset conditions encountered, should the blending of chemicals create aggressive by products that would present problems for other potential material choices.
In recent years, fuels are getting more and more complicated in terms of formulation. Gasoline, at one time, was considered simple, but now there is diesel fuel, alcohol blends, ether additives for octane adjustment, and biodiesel. In underground transport and holding systems, it is expected that the installations will last for years without the need for replacement or repair.
While these versions of fuel can usually be handled by relatively less expensive materials, each different fuel variation poses a potential disaster, should the line be required to switch fuel type at some point.
PVDF gives the very unusual combination that ensures resistance to alcohol, hydrocarbon resistance (aromatic and aliphatic), and resistance to oxidants commonly associated with the latest biodiesel technology.
In the related area of production of ethanol, it is common to have low levels of sulfuric acid generated in the process. Many processing plants began construction with stainless steel, but have now turned to PVDF-lined process equipment to avoid corrosion problems caused by low percentage acid concentrations.
Pharmaceutical and Biotechnology
The pharmaceutical industry faces several process challenges due to the sheer amount of ingredients handled. This is coupled with FDA regulations, USP Class 6 requirements, and process water purification targets. PVDF meets all these requirements and has the added advantage over common plastics that it can be repeatedly steam cleaned at up to 30 psi steam.
PVDF and PVDF copolymers are listed in the ASME Bioprocessing Equipment (ASMEBPE) standards as a common material selected by designers for biotech system design. Piping, flexible tubing, tanks, membranes and pumps are all common applications for PVDF in this industry.
Polymers for Semiconductor Processing
Perhaps, the biggest industrial use for PVDF is in the semiconductor industry. It has many properties that cater to the requirements of this industry, which are not required in case of general chemical applications. Flame and smoke resistant compliance outlined by Factory Mutual (FM) 4910 plus Underwriters Laboratories (UL 2360), and SEMI F57 high purity standards are special requirements in the manufacture of high purity piping systems and acid etching equipment used in the process of preparing silicone wafers.
The combination of chemical resistance, high purity and superior strength of PVDF compared to other high-quality materials has made it a standard material of construction in a semiconductor facility.
The nuclear reclamation industry faces several challenges. First, a series of harsh chemicals is used in the glove boxes manufactured to purify the radioactive ores. While many materials can handle chemicals like hydrochloric or nitric acid used to purify plutonium and uranium, the contact surfaces of the glove box must also handle the radioactivity associated with this process. After several years of testing and field experience, PVDF has been found to be the most radiation resistant polymer capable of long life in nuclear glove box design and waste holding equipment.
Potable Water and Wastewater
Certain grades of PVDF are listed by the National Sanitation Foundation (NSF) for use in potable water systems. Taking into account the concerns related to bacteria, bioterrorism, chlorine content of water and UV exposure for many years of service life, a material like PVDF can provide long system life even if the system parameters change over time.
In wastewater applications, there is a general concern that chemical compatibility could be unpredictable. PVDF offers an improved safety factor, should unexpected or unplanned chemical combinations occur. It is unlikely that any combination of chemicals at 140°C or below over a short period would attack PVDF in a catastrophic manner, which is more likely with metals or lower performing polymers.
Food, Dairy and Beverage
In general, food items such as sauces and fruits can have pH ranges between 2.0 and 3.5. When it comes to their processing, this can result in an aggressive environment over time. PVDF components are often machined and used in the processing of cranberry, hot sauces, alcoholic beverages and a few other relatively common foods. The abrasion resistance of PVDF and its ability to be sterilized with various chemicals and steam also adds to the attractiveness of this material for food, dairy and beverage applications.
Institutional Buildings (Laboratories)
For government research buildings, schools and universities, it is mandatory that laboratory piping and components passing through the return plenum space meet more stringent fire safety norms. Certain grades of PVDF meet the ASTM E-84 (25/50) requirement that allows materials exposed in plenums to be considered equivalent to non-combustible.
PVDF becomes attractive in these applications for waste drainage and process piping due to its high temperature capability to 150°C, excellent short-term chemical resistance to almost any chemical combination, lightweight and easy welding fabrication compared to metal or glass, and low cost compared to other material options that do all of the above, apart from meeting the 25/50 flame and smoke criteria.
A Material of Choice
Considering the distinct features of Kynar PVDF and the benefits it offers to end-users across industries, there is immense scope for further use in different applications. Known for its versatility, it can help manufacturers in diverse segments to improve their product performance.