Thermoplastics which consist of approximately 80% of crystalline structures are called semi-crystalline materials.
Their structure is ordered with some disordered areas in between.
The ordered areas give the material strength and stiffness.
Due to the higher stiffness, the material will break rather than bend when a load is applied.
Typical examples of semi-crystalline polymers are PA, POM, PP and PE.
Depending on the variation of density between processing and ambient temperature in injection molding shrinkage might appear.
Shrinkage is divided into two fields: processing and post processing shrinkage.
Processing shrinkage occurs in the mold due to volumetric contraction, mold restrains, crystallinity and orientation.
Post processing shrinkage is measured usually after 24 to 48 hours after the production.
Shrinkage happens mainly due to the relaxation of residual stresses.
Plastic granules are typically stored in small casks (sack ware), large casks (octabins) or in silos. For storage of larger tonnages of plastic, silos made from stainless steel or aluminum are used. Due to their size, silos are usually erected outside of production areas. From there, the silos are connected to the granulate conveying system of the production plant. The conveyor system first forwards the material from the silo to a central drying system before it is fed to the injection molding machines.
Linear or branched chain structures, which consist of repeating monomers are called thermoplast (also known as thermoplastic).
They can be softened and re-hardened infinite times.
Reheating temperature should not exceed a material specific maximum, as it will cause degradation of the polymers.
Typical examples of thermoplastic materials include PA, PE, PC and PVC.
Thermoplastics can be subdivided into two distinct classes: Semi-crystalline and Amorphous.
Multi-functional Polymers with the processability of thermoplasts and the elasticity of vulcanized rubbers are called TPEs (thermoplast elastomers, also known as, thermoplastic elastomers).
Like thermoplasts, it is possible to repeatedly heat them up for softening and cool them down for hardening.
TPE is used for bathmats, housing (soft grip), handles, etc.
Typical TPE-Classes are: S-TPE, COPE and TPU.
