What is oxidative degradation?
Oxidative degradation is an autocatalytic process of attack on the hydrogen atoms, to form hydroperoxides. The stability of polymers is thus inversely proportional to the number of hydrogen atoms with the carbon atoms present in the polymer chain. The degradation is catalyzed by heavy metals such as copper.
How is PVC degraded?
During processing, storage and utilization, PVC degrades as it is exposed to high temperatures, high mechanical stresses or UV light. Degradation of the polymer occurs by successive elimination of hydrogen chloride (HCl), which is called dehydrochlorination , see Fig. 20.
What is the half life of PVC?
The hydrolytic half-life is less than 10 years (calculated, 25°C) (RIPPEN, 1991).
What is oxidation in plastics?
Most polymers are subject to oxidation, and it is the most common form of plastic degradation (consider Table 2). Oxidation is a chemical reaction in which oxygen is introduced into the molecular structure of the polymer, creating a form of carbon-oxygen bonds known as carbonyl functionality.
How does oxidative degradation occur?
Oxidative degradation involves the disintegration of macromolecules by the action of oxygen on the substrate (oxidation). Free radicals are formed which react with oxygen-producing oxy- and peroxy-radicals.
How can oxidative degradation be prevented?
Both antioxidants and thermal stabilization aids can be added to WPC formulations to decrease thermal degradation during processing. In addition to protecting the polymer during processing, antioxidants can also help protect the polymer matrix during environmental exposure (Klyosov, 2007).
How long does it take for PVC to decompose?
Polyvinyl chloride- PVC: This type of plastic is stable but resistant to chemical breakdown and oxidation. To biodegrade PVC, a certain type of fungus or thermal degradation can be used. As a cling wrap, PVC takes more than 450 years to biodegrade.
What happens to PVC in the sun?
PVC does surprisingly well when exposed to ultra violet rays (sunlight). Research shows little to no effect on PVC’s tensile strength or elasticity after prolonged sun exposure. The only degradation that seems to occur is impact strength.
Does PVC degrade in sunlight?
Does PVC become brittle over time?
PVC becomes increasingly brittle as the temperature drops. When exposed to freezing temperatures for prolonged periods of time, it can become brittle enough to crack quite easily.
Does PVC oxidise?
Thermal degradation PVC is the most thermally sensitive common polymer, with major degradation occurring from ~250 °C (480 °F) onwards; other polymers degrade at higher temperatures.
What is plastic degradation?
Any physical or chemical change in polymer as a result of environmental factors, such as light, heat, moisture, chemical conditions or biological activity.
What causes polymer degradation?
In general, the effects of heat, light, air and water are the most significant factors in the degradation of plastic polymers. The major chemical changes are oxidation and chain scission, leading to a reduction in the molecular weight and degree of polymerization of the polymer.
Which of the following is used to prevent oxidative degradation of polymer?
Hindered Amine Light Stabilisers were introduced in the 1970s (Gugumus, 1975). They are derivatives of 2,2,6,6-tetramethyl piperidine. These extremely efficient stabilisers do not absorb UV radiation, but act to inhibit degradation of the polymer.
Is PVC environmentally friendly?
PVC is the most environmentally damaging plastic. The PVC lifecycle — its production, use, and disposal — results in the release of toxic, chlorine-based chemicals. These toxins are building up in the water, air and food chain.
Why is PVC not recycled?
A major problem in the recycling of PVC is the high chlorine content in raw PVC (around 56 percent of the polymer’s weight) and the high levels of hazardous additives added to the polymer to achieve the desired material quality. As a result, PVC requires separation from other plastics before mechanical recycling.
Does PVC degrade in UV?
What causes brittle PVC?
One of the most harmful things for PVC pipes is sun exposure. PVC that is run above ground and exposed to sunlight can break down faster than it normally would. The ultraviolet rays from the sun can actually break down the structure of PVC material and make it brittle and breakable.