What is meant by chain scission?
Chain scission is a term used in polymer chemistry describing the degradation of a polymer main chain. It is often caused by thermal stress (heat) or ionizing radiation (e.g. light, UV radiation or gamma radiation), often involving oxygen.
What is the most common cause of chain scission in PA 6?
Normally, chain scission is caused by exposure to elevated temperatures in combination with high shear stress, and is often associated with processing techniques where air is not present.
What is cross linked polymer?
In polymer chemistry, when a synthetic polymer is said to be “cross-linked”, it usually means that the entire bulk of the polymer has been exposed to the cross-linking method. Very high cross-link densities can cause materials to become very rigid or glassy, such as phenol-formaldehyde materials.
Why do polymers degrade?
Monomers, polymers, and plastics Degradation is often due to a change in the chemical and/or physical structure of the polymer chain, which in turn leads to a decrease in the molecular weight of the polymer. The degradation of polymers to form smaller molecules may proceed by random scission or specific scission.
What happens when a polymer degrades?
Polymer degradation is the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. The major chemical changes are oxidation and chain scission, leading to a reduction in the molecular weight and degree of polymerization of the polymer. …
What is the most common class of inorganic polymers?
Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are hybrid polymers. One of the best known examples is polydimethylsiloxane, otherwise known commonly as silicone rubber.
How do you break a polymer chain?
The polymeric chain scission is an elimination reaction that takes place by breaking the bonds that form the polymeric chain. When the reaction takes place as a successive removal of the monomer units from the polymeric chain, it is called a depolymerization.
What is oxidative degradation of polymers?
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. It takes place as a result of the simultaneous interaction of oxygen with the polymer and high temperature.
Which of the following is cross-linked polymer?
Bakelite is a condensation polymer made from formaldehyde and phenol as shown below: Thus, the correct answer is option D i.e. Bakelite is a cross-linked polymer.
What is cross-linked polymers give example?
Examples of cross-linked polymers include: Polyester fiberglass, polyurethanes used as coatings, adhesives, vulcanized rubber, epoxy resins and many more.
Why do polymers not degrade?
Long-chain polymers with all-carbon backbones such as polyolefins, polystyrene and PVC will not degrade by biological action alone and must first be oxidised to create chemical groups which the enzymes can attack.
Does rubber degrade over time?
What is rubber deterioration? Most elastomers undergo rubber degradation over time and the most common rubber deterioration causes are exposure to light, oxygen (ozone) and heat.
How does chain scission reduce molecular weight of a polymer?
Chain scission reduces the molecular weight of the macromolecules of a polymer and this finds some commercial applications in problems concerned with molecular weight control, particularly useful in the reclamation of polymer wastes. Several projects are described in the patent literature.
Where does chain scission occur during photooxidation?
During photooxidation, the oxidation occurs in the vicinity of the double bond, resulting in chain scission.254 On the other hand, the crosslinking reactions occur under aerobic and anaerobic conditions.
Where do chain Scissions occur in FRP composites?
BenzartiK. , ColinX. , in Advanced Fibre-Reinforced Polymer (FRP) Composites for Structural Applications, 2013 Chain scissions can occur at peculiar sites of high reactivity (selective chain scissions). They may also be randomly distributed if all the repeat units are equi-reactive (random chain scissions).
Which is the classic model of chain scission?
The classic model that describes chain scission in elastomers was proposed many years ago by Lake and Thomas [26 ]. The aim of the model is to calculate the energy dissipated in breaking all the polymer strands that have adjacent cross-links on either side of the crack plane.