Plastics, also known as synthetic resins, are broadly classified into two main categories: thermosetting resins and thermoplastic resins.

　　Thermosetting resins include phenolic resins and melamine resins, which, once cured by heat, no longer soften. Thermoplastic resins include polyvinyl chloride, polyethylene (PE), polystyrene (PS), and polypropylene (PP), which can be softened again by reheating.

　　Typically, thermoplastic polymers are supplied in the form of compounded pellets that already contain incorporated additives, such as antioxidants. In contrast, PVC resin is usually delivered as a powder and can be stored for extended periods because the material is resistant to oxidation and degradation. During the processing stage, various additives and pigments are introduced into the polyvinyl chloride compound, which is then converted into finished PVC products.

　　Polyvinyl chloride is sometimes referred to as “vinyl” in North America and, to a large extent, in Europe as well. In Europe, however, the term “vinyl” typically refers to specific flexible applications, such as flooring, decorative panels, and synthetic leather.

　　PVC is a thermoplastic composed of 57% chlorine (derived from industrial-grade salt) and 43% carbon (obtained from ethylene, which in turn is primarily sourced from oil and natural gas). Compared with other polymers that rely heavily on crude oil or natural gas—resources that are non-renewable—PVC can be regarded as a resource-conserving plastic. In contrast, plastics such as PE, PP, PET, and PS are entirely dependent on oil or gas. This characteristic contributes to PVC’s excellent fire-retardant properties.

　　How is PVC formed?

　　In the chemical process for producing polyvinyl chloride, we must first consider the simplest building blocks, known as monomers; during polymerization, these monomer molecules link together to form long molecular chains, which are referred to as polymers (also called macromolecules).

　　This pertains to PVC, which is produced by the polymerization of vinyl chloride monomer—commonly referred to by its acronym, VCM. Some monomers exist in reactive gaseous forms, and certain ones can pose health risks upon direct human exposure. In such cases, their manufacture and processing are conducted under strict hygiene, safety, and environmental protection controls. By contrast, polymers like PVC, which are synthesized via polymerization from monomers, are solid and chemically stable substances and therefore do not adversely affect human health. VCM, the raw material for polyvinyl chloride, is a gas at ambient temperature but is typically stored in liquid form under pressure. Ethylene and chlorine serve as the feedstocks for polyvinyl chloride. The upstream industry comprises those that supply these materials, including the production of basic petrochemicals (sometimes called “feedstocks”), which provide ethylene, as well as the chlor-alkali industry, which supplies chlorine gas.

　　Ethylene and propylene, along with other basic petrochemicals, are primarily produced via the thermal cracking of naphtha or natural gas. Naphtha, in particular, is mainly supplied by the petroleum refining industry, which uses crude oil as its feedstock. Meanwhile, the chlor-alkali industry produces caustic soda, chlorine, and hydrogen through the electrolysis of industrial-grade brine as the primary raw material.

　　In the PVC production process, ethylene and chlorine are first combined to form an intermediate called vinylidene chloride; this is then converted into vinyl chloride, the basic building block of polyvinyl chloride, or PVC. During the “polymerization” process, vinyl chloride molecules link together to form the PVC polymer chain. Polyvinyl chloride produced by this method is in the form of a white powder. It is not used on its own but is instead blended with other ingredients to create a wide range of finished products.

　　Most plastics are composed primarily of carbon and hydrogen. Polyvinyl chloride (PVC), however, contains chlorine—about 57% by weight—along with carbon and hydrogen. The presence of chlorine makes PVC particularly versatile, as it confers broad compatibility with other materials. The high chlorine content also imparts flame-retardant properties to PVC. Furthermore, the chlorine content can serve as a “marker” for identifying PVC in automated sorting systems used for plastic recycling. PVC formulations can be shaped using a variety of processing techniques while requiring relatively low energy input, enabling the production of final product forms. The PVC polymer itself is chemically stable, chemically neutral, and non-toxic. PVC formulations find extensive applications, ranging from highly sensitive uses such as medical devices to construction, automotive, and electrical wiring.

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