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The chemical bond in a polymer backbone may be broken with the generation of free radicles by heat, ionizing irradiation, mechanical stress and chemical reactions. These scissions multiply in number and cause a fracture tip initialization to occur followed by its growth. [3]
In polymer science, the polymer chain or simply backbone of a polymer is the main chain of a polymer. Polymers are often classified according to the elements in the main chains. The character of the backbone, i.e. its flexibility, determines the properties of the polymer (such as the glass transition temperature).
Forensic polymer engineering is the study of failure in polymeric products. The topic includes the fracture of plastic products, or any other reason why such a product fails in service, or fails to meet its specification. The subject focuses on the material evidence from crime or accident scenes, seeking defects in those materials that might ...
The third region shows the formation of a neck, and the fourth region is characterized as a steep increase in stress due to viscous flow. Additionally, region four corresponds to alignment and elongation of the polymer backbone from its coiled or folded state—eventually leading to fracture. [24] [25]
Crazes in polystyrene (PS). Crazing is a yielding mechanism in polymers characterized by the formation of a fine network of microvoids and fibrils. [1] [2] These structures (known as crazes) typically appear as linear features and frequently precede brittle fracture.
During chain cleavage, the polymer chain is broken at a random point in the backbone to form two - mostly still highly molecular - fragments. [3] Depolymerization, on the other hand, is the elimination of low molecular weight substances (monomers, dimers and suchlike) from a polymer. [4]
Fractography is the study of the fracture surfaces of materials. Fractographic methods are routinely used to determine the cause of failure in engineering structures, especially in product failure and the practice of forensic engineering or failure analysis.
In contrast, chain scission occurs when a carbon-centered radical on the polymer backbone reacts with another free radical, typically from oxygen in the atmosphere, causing a break in the main chain. Free radicals can also undergo reactions that graft new functional groups onto the backbone, or laminate two polymer sheets without an adhesive. [17]