Polyvinyl Chloride, commonly known as PVC, is a common plastic polymer recognized for its durability and low cost, utilized widely in construction, plumbing, and industrial applications. This material is often chosen for its robust nature and resistance to chemical attack. Although PVC exhibits strong resistance to a broad range of substances, it is not universally inert to all chemicals. Understanding the specific limitations of PVC’s chemical compatibility is necessary to prevent material failure and ensure system longevity.
General Chemical Resistance Profile
PVC demonstrates excellent resistance to many common corrosive agents encountered in industrial and household settings. Its strong chemical stability stems from stable carbon-chlorine bonds within the polymer structure, which are difficult to break. The material is largely unaffected by water, most inorganic salts, and non-polar aliphatic hydrocarbons. PVC is also highly compatible with weak to moderately concentrated inorganic acids and bases. For instance, PVC can safely handle hydrochloric acid at all concentrations and sulfuric acid up to 90% concentration below 60°C. Alkalis, such as sodium hydroxide, will not attack PVC even at high concentrations and temperatures up to 60°C. This broad resistance profile makes PVC a preferred material for wastewater treatment, chemical processing, and municipal sewerage networks.
Specific Chemicals That Degrade PVC
Despite its general hardiness, PVC is vulnerable to certain categories of organic compounds, which actively attack and compromise its structure. The primary threat comes from organic solvents, whose polarity allows them to penetrate the polymer chains effectively. This penetration causes the PVC to swell, leading to a reduction in its tensile strength and eventual structural failure or dissolution. Specifically, chemicals like ketones, including acetone and methyl ethyl ketone (MEK), and aromatic hydrocarbons such as benzene and toluene, should not be used with PVC. These strong solvents absorb into the material, a principle seen in the use of solvent cement to intentionally fuse PVC pipes together. Strong oxidizing agents, such as highly concentrated nitric acid, can also chemically degrade the material, particularly at elevated temperatures.
Environmental and Physical Factors Affecting Performance
The chemical resistance of PVC is intrinsically linked to the operating environment and physical stresses placed upon the material. A primary factor is temperature, as higher temperatures significantly accelerate the rate of chemical attack. Increasing the temperature increases the molecular motion within the polymer, making it more susceptible to penetration, even by chemicals that are normally benign. The concentration of a chemical also plays a substantial role, as a substance harmless in dilute form can become destructive at high concentrations. For example, a high concentration of an organic solvent will cause swelling and softening, even if low concentrations are safe. Furthermore, mechanical stress, such as constant internal pressure or external loads, can greatly reduce the material’s resistance, leading to Environmental Stress Cracking. This type of cracking occurs when a chemical agent combines with mechanical tension to induce material failure.