Polyvinyl Chloride (PVC) is a widely utilized synthetic plastic material found in numerous products. It is recognized for its durability, versatility, and adaptability. PVC’s widespread use stems from its inherent properties, which include a notable resistance to various chemical substances.
The Chemical Makeup of PVC
PVC’s chemical resistance originates from its unique molecular structure. The polymer chain of PVC consists of repeating units where a chlorine atom is bonded to every other carbon atom. This presence of chlorine, accounting for approximately 57% of PVC’s mass, fundamentally distinguishes it from other common plastics like polyethylene, which are composed solely of carbon and hydrogen atoms.
The strong carbon-chlorine bonds within the PVC structure contribute significantly to its stability and reduced reactivity, making it less susceptible to degradation when exposed to many substances. While PVC can be manufactured in both rigid (unplasticized, PVC-U) and flexible (plasticized, PVC-P) forms, with plasticizers added to enhance flexibility, the foundational chemical structure provides a stable basis for its resistance properties.
Chemicals That PVC Resists
Polyvinyl Chloride demonstrates a broad resistance to numerous chemical categories. It is largely unaffected by most mineral acids, bases, and salts. This includes common inorganic acids like hydrochloric acid, which PVC can handle at various concentrations and temperatures up to 60°C. Sulfuric acid, at concentrations below 90%, also typically has no effect on PVC up to 60°C.
PVC also exhibits strong resistance to alkalis, remaining unaffected by them at all concentrations up to 60°C. Beyond acids and bases, PVC is resistant to many alcohols, fats, and oils. It can also withstand aromatic-free petrol and de-ionized or distilled water.
Chemicals That PVC Does Not Resist
Despite its general robustness, PVC is not impervious to all chemical attacks, and certain substances can significantly degrade or dissolve it. Aromatic hydrocarbons, such as benzene and toluene, are known to have a detrimental effect on PVC. Similarly, chlorinated hydrocarbons, including carbon tetrachloride and chloroform, can cause substantial damage.
Ketones, such as acetone and methyl ethyl ketone (MEK), can cause PVC to swell or even dissolve. Esters and ethers also pose a threat, as PVC can absorb these substances, leading to swelling and a reduction in tensile strength. Strong oxidizing agents can also cause superficial attack, particularly at elevated temperatures or in concentrated solutions.
Factors Influencing Chemical Resistance
The chemical resistance of PVC is not an absolute property; several factors can influence its performance when exposed to various substances. Temperature plays a significant role, as higher temperatures generally accelerate chemical reactions and can reduce PVC’s resistance, leading to faster degradation. PVC has a relatively low maximum operating temperature, typically around 60°C (140°F), above which its susceptibility to damage increases.
The concentration of a chemical also affects PVC’s resistance; higher concentrations typically increase the risk of degradation. The duration of exposure is another important consideration, as prolonged contact, even with substances PVC generally resists, can eventually lead to some level of attack or absorption. Additionally, the presence of plasticizers in flexible PVC can alter its chemical resistance, often making it more susceptible to certain solvents compared to rigid PVC.
Practical Uses of PVC’s Chemical Resistance
PVC’s notable chemical resistance makes it an invaluable material in numerous practical applications. Its ability to withstand a wide array of acids, alkalis, and salts makes it a preferred choice for piping systems that transport water, wastewater, and various industrial chemicals. This property is also leveraged in the construction industry for drain, waste, and vent (DWV) systems, as well as in underground drainage.
The material’s resistance to corrosion allows its use in industrial linings, laboratory equipment, and chemical storage tanks. Furthermore, PVC’s inertness contributes to its utility in protective clothing and certain medical applications, where contact with chemicals necessitates a durable and non-reactive barrier.