Example of Thermal Degradation: How Heat Breaks Down Everyday Materials

An everyday example of thermal degradation is overheated PVC wire insulation: when exposed to sustained high temperatures (typically above roughly 140–200°C without adequate stabilizers), the plastic begins to decompose, releasing pungent hydrogen chloride (HCl), discoloring from yellow to brown/black, and becoming brittle. More broadly, thermal degradation is the breakdown of a material’s chemical structure due to heat, which can change color, weaken mechanical properties, emit harmful gases, or create residues and char.

What Thermal Degradation Means

Thermal degradation describes chemical and physical changes that occur to materials when the energy from heat breaks molecular bonds or accelerates reactions, often in combination with oxygen or moisture. The results range from subtle property loss to complete charring or volatilization, and the process can be autocatalytic—once it starts, byproducts can accelerate further breakdown.

A Concrete, Real-World Example: PVC Wire Insulation

What happens to PVC when it overheats

Polyvinyl chloride (PVC) is widely used as electrical wire insulation. When PVC is overheated—due to current overloads, poor electrical connections, or installation near heat sources—it undergoes dehydrochlorination. This reaction strips hydrogen chloride (HCl) from the polymer backbone, creating conjugated double bonds that cause yellowing, then browning and blackening. The released HCl can corrode nearby metals (notably copper conductors), and the insulation becomes stiff, brittle, and prone to cracking.

Typical temperature ranges and why stabilizers matter

Unstabilized PVC can begin degrading in the approximate range of 140–180°C, while processing and some service conditions may push material temperatures into that zone if controls fail. Manufacturers blend heat stabilizers (e.g., calcium/zinc or organotin systems) to raise the onset temperature of degradation and slow the reaction, but persistent overheating can still trigger decomposition, discoloration, and embrittlement over time.

Why This Matters

Thermal degradation matters because it often compromises safety and reliability. In electrical systems, degraded insulation increases the risk of short circuits, corrosion, smoke, and toxic emissions. In consumer goods and industrial components, it shortens service life, increases maintenance costs, and can lead to performance drift or catastrophic failure. Recognizing the signs and causes helps prevent incidents and extend component longevity.

Other Common Examples Across Materials

Beyond PVC, a range of everyday materials undergo thermal degradation under sustained or excessive heat. The following examples illustrate how different chemistries fail in distinct ways, with consequences for safety, performance, and health.

• Polyethylene and polypropylene: At elevated temperatures, especially with oxygen present, chain scission and oxidation form carbonyl compounds, causing embrittlement, cracking, and loss of toughness; at higher temperatures, pyrolysis yields waxes and gases.
• Cooking oils: Prolonged heating near or above frying temperatures (~180°C) leads to breakdown of triglycerides, polymerization, and formation of irritating or harmful aldehydes; glycerol can dehydrate to acrolein, producing a sharp, pungent odor.
• Wood and paper: Thermal degradation (pyrolysis) begins around 200–300°C, producing char, tar, and volatiles; as volatile gases ignite, charring accelerates and structural integrity deteriorates.
• Nylon and other polyamides: Heat can induce chain scission and, if moisture is present, hydrolysis; parts can lose strength and creep resistance, especially above their designed service temperatures.
• Epoxy composites: Above the glass transition temperature (Tg), resins soften and can undergo oxidative degradation; prolonged overheating leads to microcracking, delamination, and char formation.
• Lithium-ion battery electrolytes: Elevated temperatures can decompose LiPF6-based electrolytes and carbonate solvents, generating gases and heat; under abuse conditions this contributes to thermal runaway.

Taken together, these examples show that thermal degradation isn’t confined to one sector; it affects plastics, natural materials, energy systems, and even food preparation, each with its own warning signs and failure modes.

How to Reduce the Risk

Mitigating thermal degradation involves controlling temperature, limiting exposure to oxidizing conditions, and selecting materials designed to withstand the expected heat load. The following strategies are commonly used across industries and applications.

• Stay within rated service temperatures: Choose materials with appropriate heat resistance and observe manufacturer limits for continuous and peak temperatures.
• Improve thermal management: Use heat sinks, ventilation, spacing, and insulation to avoid hotspots; ensure good electrical connections to minimize resistive heating.
• Use stabilizers and antioxidants: For polymers, add heat stabilizers, UV absorbers, and antioxidants to delay onset of degradation.
• Limit exposure time: Degradation depends on both temperature and duration; reduce dwell times at high heat during processing or use.
• Monitor and maintain: Inspect for discoloration, odor, brittleness, or warping; replace compromised parts before failure propagates.
• Design for safety: In electrical systems, use thermal fuses, current limiting, and proper derating; in cooking, filter and refresh oils to minimize breakdown products.

Applying these practices helps extend component life, maintain performance, and reduce safety hazards associated with heat-driven deterioration.

Summary

A clear example of thermal degradation is overheated PVC wire insulation, which releases HCl, discolors, and becomes brittle as its polymer chains break down. Similar heat-induced failures affect many materials—from plastics and composites to wood and cooking oils—underscoring the importance of temperature control, material selection, and preventive maintenance to avoid property loss, corrosion, and safety risks.