Semi-crystalline materials polymers

Thus far we have considered the influence of the interphase in relation to the mechanical properties of semi-crystalline linear polymers, in particular for the case of UHMW-PE, i.e. its role in the drawability or in the welding of such materials. With the recent advent of synthesis routes to produce highly controlled model systems, the investigation of the interphase can be extended further. 

In a final chapter a closely related phenomenon, the formation of shear bands in semi-crystalline polymers under compressive load will be described. It is attempted to discuss under which conditions shear bands are formed in semi-crystalline materials and how they interact with each other or with certain microstructural features, finally leading to crack initiation and shear fracture of the bulk polymer. 

Post-failure studies of the fracture surface morphology of bulk semi-crystalline polymers are more difficult than those of amorphous materials due to the more complex multiphase structure associated with semi-crystalline materials However, it was shown that some fractographic details point to the formation of a stress whitened region ahead of a notch prior to final fracture of the material. In particular, stress-whitened regions were easily visible in semi-crystalline polymers such as LDPE and HDPE The resulting, macroscopically apparently brittle fracture... 

As already mentioned there are only very few studies dealing with the formation of shear bands in semi-crystalline materials. Some recent papers on oriented and non-oriented semi-crystalhne polymers have indicated that under... 

All materials belong to the class of semi-crystalline thermoplastic polymers. Characteristic appearances of spherulitic microstructures of the polymers are shown in Figures 4 and 5 for the examples of POM and PA66. 

Haudin, J. M. (1982) Plastic deformation of semi-crystalline polymers, in Plastic Deformation of Amorphous and Semi-Crystalline Materials, edited by Escaig, B. and G Sell, C., Les Ulis Les Editions de Physique, pp. 291-311. 

The polymer must be amorphous. In semi-crystalline materials, the crystallites must melt prior to dissolution. 

Tables in this chapter contain published pressure-volume-temperature data for amorphous homopolymers. Measurements below the melting temperatures for semi-crystalline materials are not included because of the potentially large variance among samples with differing degrees of crystallinity. Rogers [1] and Zoller [2] have also compiled equation-of-state data for amorphous polymers.

J.M. Haudin, Plastic deformation of semicrystalline polymers, in Plastic Deformation of Amorphous and Semi-crystalline Materials, ed. by B. Escaig, C. G Sell (Les Editions de Physique, Paris, 1982), p. 291... 

PE is a crystalline polymer. The namre of the soft chain of PE makes it easier for the molecules to form crystals when cooling from molten status to a solid one. Imagine that a single long chain molecule is in favour of forming a random coiled state. When people talk about crystalline polymers, they actually mean semi-crystalline polymers. This is because, unlike most inorganic crystalline materials, polymers cannot be 100% crystalline. They always consist of, at least, two phases amorphous and crystalhne. 

Depending on the molecular weight, PCL as a homopolymer has degradation times ranging from 2 to 4 years (Woodruff and Hutmacher, 2010) (Table 3.3). It is a semi-crystalline material, which means the degradation initiates in the amorphous regions of the polymer, while the crystalline phase initially will stay unaffected. As a result, the mechanical properties of the implant will not be influenced in a significant way. 

Solvay further boosted its polymer portfolio in January 2006 with the acquisition of Mississippi Polymer Technologies a start-up company whose main attraction is the PARMAX family of melt-processable, transparent, amorphous, rigid-rod thermoplastics which are claimed to exhibit a unique combination of strength, stiffness and hardness. The chemical resistance of PARMAX is claimed to be comparable with semi-crystalline materials and to be unsurpassed by any other transparent polymer. 

Crystallisation can also occur in the solid state. This is usually associated with semi-crystalline materials that crystallise rather slowly and therefore can be quenched into a glassy solid. A well known example of this type of polymer is poly(ethylene terephthalate). Upon heating to just above its glass transition temperature, crystallisation starts. This is known as cold crystallisation. 

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