The structure of crystalline polymers crystallized from the melt in rapid cooling conditions
The structure of crystalline polymers crystallized from the melt in rapid cooling conditions
The structure of high density linear polyethylene in investigated by Infrared and Unman spectroscopy, X-Ray diffraction and thermal analysis. It is shown that ultra-rapidly quenching the molten polymer into cryogenic refrigerants produces a glassy solid. Crystallization from the glass occurs at the remarkably low temperature of ti 170K, the material so produced, once warmed to room temperature shows all the characteristics of polyethylene crystallized from the melt without the involvment of an intermediate glassy phase. The very low temperature at which the crystallization from the glass occurs points to a close relationship between the structure of the glass, hence that of the melt, and the structure of the material produced from it. This observation casts doubts on the widely accepted chain folded lamellar model of semicrystalline polymers. The existence of a relationship between the structure of the melt and that of the solid produced from it by rapid cooling in then investigated. It is shown that increasing the melt temperature before quenching results in a reduction in the thickness of the crystalline zones present in the solid. This observation cannot be accounted for by the folded chain lamellar model. An alternative model, involving chains meandering through neighbouring lamellae is proposed. The investigation is extended to a helical polymer; Isotactic Polypropylene. The rapid quenching of this polymer from the melt to below its glass transition temperature produces a glassy material. Heating that material to room temperature results in the production of the paracrystalline (or 'smectic') phase. During the glass paracrystal transition, helical segments approximately 1004 long are produced but very little or no packing of the chains into a well defined crystalline array occurs. 'Annealing' of the paracrystalline material above 320K initiates its crystallization into the monoclinic (d) crystalline form. The kinetics of the various transitions are investigated, it is proposed that the structure of the paracrystalline phase is close to that of the melt, the major difference between the two being the growth of the regular helical segments. It is concluded that the structure of the melt governs that of the crystalline material produced from it in rapid cooling conditions. It is proposed that the structural factor which influences the characteristics of the resulting crystalline material is the convolutions of the molecules in the melt.
University of Southampton
1978
Glotin, Michel
(1978)
The structure of crystalline polymers crystallized from the melt in rapid cooling conditions.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The structure of high density linear polyethylene in investigated by Infrared and Unman spectroscopy, X-Ray diffraction and thermal analysis. It is shown that ultra-rapidly quenching the molten polymer into cryogenic refrigerants produces a glassy solid. Crystallization from the glass occurs at the remarkably low temperature of ti 170K, the material so produced, once warmed to room temperature shows all the characteristics of polyethylene crystallized from the melt without the involvment of an intermediate glassy phase. The very low temperature at which the crystallization from the glass occurs points to a close relationship between the structure of the glass, hence that of the melt, and the structure of the material produced from it. This observation casts doubts on the widely accepted chain folded lamellar model of semicrystalline polymers. The existence of a relationship between the structure of the melt and that of the solid produced from it by rapid cooling in then investigated. It is shown that increasing the melt temperature before quenching results in a reduction in the thickness of the crystalline zones present in the solid. This observation cannot be accounted for by the folded chain lamellar model. An alternative model, involving chains meandering through neighbouring lamellae is proposed. The investigation is extended to a helical polymer; Isotactic Polypropylene. The rapid quenching of this polymer from the melt to below its glass transition temperature produces a glassy material. Heating that material to room temperature results in the production of the paracrystalline (or 'smectic') phase. During the glass paracrystal transition, helical segments approximately 1004 long are produced but very little or no packing of the chains into a well defined crystalline array occurs. 'Annealing' of the paracrystalline material above 320K initiates its crystallization into the monoclinic (d) crystalline form. The kinetics of the various transitions are investigated, it is proposed that the structure of the paracrystalline phase is close to that of the melt, the major difference between the two being the growth of the regular helical segments. It is concluded that the structure of the melt governs that of the crystalline material produced from it in rapid cooling conditions. It is proposed that the structural factor which influences the characteristics of the resulting crystalline material is the convolutions of the molecules in the melt.
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Published date: 1978
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Local EPrints ID: 458379
URI: http://eprints.soton.ac.uk/id/eprint/458379
PURE UUID: 8f9d45fb-f175-4a5d-8cfd-43a1de4f1ec0
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Date deposited: 04 Jul 2022 16:48
Last modified: 04 Jul 2022 16:48
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Author:
Michel Glotin
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