Abstract
Structure transitions and mechanism of the formation of superlattices lamellae in microporous polyolefin (polyethylene and polypropylene) films obtained in the process based on polymer melt extrusion followed by annealing, uniaxial extension and thermal fixation have been studied by statistical analysis of electron microscopy images of the film surface. The structure of the porous films prepared in the multistage process has been studied by SEM, gravimetry and permeability measurements. It has been shown that the pore formation at the stage of uniaxial extension is accompanied by the ordering of lamellae and their self-organization controlled by spin draw ratio and annealing temperature. It was established that an increase of these parameters lead to the transition of disorder-order type. The effect of preparation conditions on the ordering process of regular spatial lattices of lamellae has been discussed.
Highlights
At present time a large number of porous systems containing microscopic pores have been prepared and studied; and among them, polyolefin films are the most promising materials
Due to a very low number of tie chains in amorphous regions the pores appear between lamellae at uniaxial extension of hard elastic samples in air at room temperature
The second type is associated with the periodic spatial superlattice of lamellae due to the disorder–order transition and ordering of particle aggregates.The percolation transition leads to the formation of a liquid-permeable porous structure and the self-organization of lamellae at increasing the control parameters of the process: λ, Tann and ε
Summary
At present time a large number of porous systems containing microscopic pores have been prepared and studied; and among them, polyolefin films are the most promising materials. The thermal treatment of these samples at temperatures close to the melting temperature of a polymer leads to an increase in the degree of crystallinity and a decrease in the number of tie chains in amorphous regions between lamellae, and, almost all tie chains become stressed In result of such structure formation the materials (films and fibers) acquire so-called “hard elastic” mechanical properties, that is, high elastic modulus and ability to large reversible deformations.[4,7] Due to a very low number of tie chains in amorphous regions the pores appear between lamellae at uniaxial extension of hard elastic samples in air at room temperature. Dering effects at the self-organization of lamellar structure in the polyolefin porous films
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