Many polymers, including vinyl, require additives to become useful finished products. These additives include heat and light stabilizers, which are used in vinyl formulations to prevent degradation during processing. The principal metals from which stabilizers are made include tin, barium, zinc, calcium and, to a much less degree, cadmium and lead. These choices in stabilizers allow for vinyl products to be formulated to meet a broad range of performance requirements.
Stabilizers are typically used at fairly low levels in the overall vinyl formulation, often at less than 2 percent. Because the metals comprise only a portion of the stabilizer package, actual metal levels are even lower. Due to the physical properties of vinyl, stabilizers and other additives are tightly held within the vinyl polymer matrix, limiting the potential for human contact or release to the environment.
The particular type and amount of stabilizer used will depend on the performance requirements of the application involved, such as rigid versus flexible, interior versus exterior, or clear versus opaque. For some applications, the choice of stabilizer is controlled by regulatory agencies or certification parties. In particular, NSF International certifies water pipe for composition and performance, and PVC pipe with the “NSF Mark” complies with the relevant drinking water standards recognized by public health officials and the U.S. Environmental Protection Agency (EPA). Also, the U.S. Food and Drug Administration (FDA) has established regulations which control the use of stabilizers for PVC products used in food and drug applications.
Tin-based stabilizers have been used for more than 40 years, and today there is a wide range of compounds available for use in many different applications. While providing excellent heat stability, they also assist in the processing of vinyl and contribute to the durability of the final product. Because of their resistance to weather, they are used in outdoor building applications such as vinyl siding, window profiles, fencing, decking and railing. Some tin stabilizers offer outstanding transparency and clarity, and these can be used in food and beverage containers, food wrap, and blister packaging for pharmaceuticals and other consumer products.
Comprehensive studies on tin stabilizers have concluded that they do not present a health or safety risk to workers, and that there are no expected environmental risks associated with their use, because they are firmly held within the vinyl matrix,. In fact, the use of tin stabilizers in vinyl used for food packaging and drinking water delivery pipe has been continuously and extensively evaluated and approved by regulatory agencies throughout the world.
Tributyltins (TBT) are not used as vinyl stabilizers. These compounds have been used by other industries in the past for their biocidal properties – that is, to prevent the grown of microorganisms such as bacteria or fungi. One major application for these materials has been as anti-foulants in marine paints to prevent the growth of barnacles, seaweed and other organisms on the hulls of ocean vessels. Commercial tin stabilizers used by the vinyl industry exhibit no biocidal properties, and it is important that they not be confused with tributytins.
Lead-based stabilizers are used principally in vinyl wire and cable jacketing and insulation are contained within the product. Building wire must meet Underwriter Laboratories® insulation standards. While vinyl wire and cable products that do not use lead stabilizers are available, in some applications the cost/performance tradeoffs are significant.
Health, Safety, and the Environment
The vinyl industry has made significant progress to improve its environmental, health and safety performance. That accomplishment has come through the industry's commitment to the following guiding principles:
- To seek and incorporate public input regarding our products and operations
- To provide chemicals that can be manufactured, transported, used and disposed of safely
- To make health, safety, the environment and resource conservation critical considerations for all new and existing products and processes
- To provide information on health or environmental risks and pursue protective measures for employees, the public and other key stakeholders
- To work with customers, carriers, suppliers, distributors and contractors to foster the safe use, transport and disposal of chemicals
- To operate our facilities in a manner that protects the environment and the health and safety of our employees and the public
- To support education and research on the health, safety and environmental effects of our products and processes
- To work with others to resolve problems associated with past handling and disposal practices
- To lead in the development of responsible laws, regulations and standards that safeguard the community, workplace and environment
In keeping with these principles, the vinyl industry encourages suppliers of vinyl stabilizers -- and, in fact, suppliers of all additives -- to maintain active research programs into the HS&E aspects of their products and to provide this information to the industry. The potential health and safety effects of individual stabilizers are fully detailed by these manufacturers in their “material safety data sheets” (MSDS), which are required by U.S. law. These are available to anyone who wishes to review them and must be provided to all workers in manufacturing plants.
Recent studies also affirm that disposal of metal-stabilized vinyl waste in landfills poses no appreciable risk to human health or the environment, because very little of the metal stabilizers leach from discarded products. In fact, vinyl membranes, termed sheet geomembranes, have been used to line landfills to prevent leakage of refuse leachate into groundwater, because of their strength and durability.