Polyvinyl chloride (PVC) is one of the most widely used forms of plastic in the world. It is durable, versatile, and inexpensive to produce, with applications in dozens of industries, from commercial building materials to children’s toys. PVC is also a leading material choice in radio frequency (RF) welding. Its flexibility, polar molecular structure and high dielectric loss properties are well suited to the manufacture of many kinds of thermoplastic products requiring robust hermetic seals. Medical IV and blood bags, surface covers such as curtain walls and tarpaulins, recreational equipment, and many other products are currently manufactured from PVC using high frequency welding processes.
But there is a dark side to PVC that has drawn increasing scrutiny from environmental groups and regulatory agencies. At all phases of its lifecycle, PVC is a major source of environmental and biological toxicity. As a result, there is a large-scale shift away from its use, and numerous industries already have measures in place to reduce or entirely eliminate PVC from their products.
What options does that leave for manufacturers? In the specialized world of RF welding, there are several excellent material substitutes that offer many of the same benefits as PVC, without its inherent drawbacks.
PVC vs. other plastics
To understand the growing restrictions on PVC use, it is important to consider some of the key differences between PVC and other thermoplastics.
PVC is the only major form of plastic that contains chlorine. It is manufactured from two feedstocks – ethylene dichloride (EDC) and vinyl chloride monomer (VCB) – using a highly energy intensive process that consumes large volumes of chlorine gas. PVC is classified as an organochlorine, a group of hazardous compounds linked to specific human health risks. PVC is approximately 57 percent chlorine by weight.
The use and presence of chlorine in PVC is at the heart of its environmental and health impact. During production of chlorine, which is achieved by splitting salt molecules (NaCl) into caustic soda and chlorine gas, hazardous by-products including mercury are released into the environment. The synthesis of PVC feedstock materials also generates large quantities of chlorine-rich wastes such as dioxins and polychlorinated biphenyls (PCBs), compounds with long-lasting toxicity. Additional dioxins are generated during accidental or intentional incineration of PVC materials and their related waste products.
How are PVC substitutes different? Most other plastics do not contain chlorine. Polyolefins, for example, are produced by the polymerization of naturally occurring organic hydrocarbons called olefins (alkenes), derived from oil or natural gas. The absence of chlorine in polyolefins such as polyethylene (PP), polypropylene (PE), and ethyl vinyl acetate (EVA) offers significant environmental and health advantages during manufacturing and product use as well as disposal.
Unlike many other plastics, PVC is rigid and brittle in its pure form. It is also inherently unstable at high temperatures. To improve its performance, several types of additives are incorporated during manufacturing.
For example, stabilizers are added to PVC to increase thermal stability. The most common stabilizers are lead, cadmium, and organtoins derived from tin. These heavy metals are potent toxins that are not chemically bound during PVC manufacturing and can leach out over time. They do not degrade after disposal, and when burned, are released into the air or create ground pollution as ash residues.
Plasticizers, primarily phthalates, are blended with PVC to make it more flexible. Phthalates are known carcinogens and neurotoxins that are under increasing scrutiny by regulatory agencies. Like stabilizers, they are not chemically bonded and leach into the air and water. Phthalates are also released into the environment in a large quantities during PVC formulation and molding.
How are PVC substitutes different? While all thermoplastics use some type of additives to enhance specific performance characteristics, petroleum-based plastics such as polyolefins typically require fewer additives that are less harmful than those used to make PVC. EVA, for example, is considered a safer alternative to PVC for many products (including those marketed for infant use) because it does not require a plasticizer.
Polyethylene teraphthalate (PET), another RF-weldable alternative, often contains an additive to improve UV stability. However, the compounds used in manufacturing PET have been extensively studied and have demonstrated no evidence of toxicity. PET also meets the strict standards for food and beverage packaging applications set by the Food and Drug Administration.
Choosing non-PVC plastics for RF welding
Manufacturers in many industries are actively looking to replace PVC materials with less toxic plastics. This, in turn, is driving the development of new plastic technologies and techniques and increasing the number of non-PVC options suitable for RF welding.
RF welding can be applied to any flexible thermoplastic material containing dipole molecules.
The layers of materials being welded can be similar or can combine different plastics, depending on the application. During the welding process, high frequency electromagnetic energy causes the polar molecules in each layer to oscillate rapidly and align to the electromagnetic field within the welding bars. The resulting heat allows the layers of materials to melt and fuse together, forming a strong seal.
The list of RF-sensitive plastics includes a number of versatile alternatives that offer less toxic, more environmentally friendly profiles compared to PVC. Ideally, any thermoplastic material substituted for PVC should also be easily recyclable. If not recyclable, it is important to understand its environmental impact if incineration is required (such as medical waste).
- Thermoplastic urethanes (TPU). TPU is increasingly used in the medical field as a substitute for PVC because it is manufacturered without plasticizers (phthalates) or other toxic chemical treatments.
- Polyamides. This term includes a variety of materials, including nylon as well as naturally occurring materials such as wool and silk. Its health and environmental profile depends on the specific type of nylon material and related by products generated during manufacturing.
- Polyethylene teraphthalate (PET). PET has been well studied for human safety and is used to manufacture water bottles and food containers. It is also easily recyclable. A wide variety of products are made from recycled PET.
- Acrylonitrile butadiene styrene (ABS). ABS is a plastic resin that has been shown to be stable and non-leaching, and does not contain plasticizers. It also recyclable. Several grades of ABS are suitable for RF welding.
- Ethyl vinyl acetate (EVA). EVA is a highly elastic material that is considered safe by the Food and Drug Administration for applications including food production, packaging, toys, and transportation. It does not contain plasticizers.
It is also possible to weld materials that do not contain dipole molecules, such as polypropylene and polyethylene. By combining PE with a dipole material such as EVA, for example, the resulting material is rendered RF sensitive.
The experts at SealWerks are happy to provide more information on PVC alternatives that combine safer chemical profiles with high quality performance, and to help you select the right plastic for your project.
Contact us today for your RF Welding product assessment.