Semi-crystallinity in polymers is a commonly misunderstood concept since it cannot be demonstrated or easily visualized. Semi-crystalline polymers have all the softening characteristics of an amorphous polymer combined with the melting characteristics associated with semi-crystalline behavior.
Question: What is different between melting amorphous and semi-crystalline polymers during recovery.
note: I have addressed this in two blog posts.
Semi-Crystalline Polymers: Like amorphous polymers, these polymers get much of their strength through chain entanglement and inter-molecular attraction. The difference is that semi-crystalline polymers have small portions of the long polymer chains that align into neatly packed and arranged semi-crystalline sites known as semi-crystalline regions. These small compact sites are points where the polymer has higher strength and increased rigidity contributing to the overall strength of the part. When melting semi-crystalline polymer, these semi-crystalline sites remain in tact until the polymer reaches a specific ‘melt’ temperature where the semi-crystalline sites dissolve. If not properly heated, the semi-crystalline sites remain in tact and the polymer chains will actually rip apart resulting in polymer chain degradation. For this reason, semi-crystalline polymers prefer to receive a lot of heat first and a small amount of shear in the end to compete the melting.