Title: Possibility of controlling the crystallinity of branched polymers crystallized from the melt
Abstract: POLYETHYLEI~E with a large molecular weight will crystallize almost instantly, so tha t even the initial crystallinity of branched products is such tha t on cooling the melt below the melting temperature it will be independent of the rate of cooling. An orderly arrangement of the polymer chains will occur even in dilute solutions of polyethylene during its crystallization [1]. The only method of changing the degree of crystallinity of polyethylene (PE) is to heat the sample thus producing disorder of the polymer chains. In the case of a polydisperse polymer, i.e. any industrial PE product, bearing in mind the irregular distribution of orderly and randomly arranged parts, this process will not be uniform and will spread, with rising temperature, to all the larger crystalline formations. I t is essential for the s tudy of the effect of crystallinity on the properties of the polymer to alter the sample temperature from test to test; this naturally makes the interpretation of the results rather difficult. We developed an experimental technique of changing the degree of crystallinity of bulk PE and of retaining any degree of crystallinity required at a particular temperature. EXPERIMENTAL Low density PE of type P 2015 I~k in the form of a 4 mm thick block (press-moulded at 5000 kg/cm z and 150°C) was allowed to soak in transformer oil at 95-100°C until equilibrium was reached (about 80% transformer oil by weight of original polymer). This PE was cooled to room temperature, the transformer oil extracted with organic solvents (o-xyleno, benzene, toluene) and the solvent evaporated (both these processes were carried out at room temperature). X-ray diffractometry was used to check on the changes of crystallinity. The instrument used for this purpose was a U.R.S.-50 IM diffractometer and a low-angle scattering chamber KRM-1. Structural studies of the sample were carried out in addition to this, using electron microscope U.E.M.V-100. The sample soaked in transformer oil was broken up and monolayer carbon replicas were made from the fractured surface (after removal of the transformer oil
Publication Year: 1968
Publication Date: 1968-01-01
Language: en
Type: article
Indexed In: ['crossref']
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