Gel-to-Solid Transition in Polyethylene from the Viewpoint of the Crystallization Process

Пахомов, П. М.; Khizhnyak, S. D.; Reuter, Hans; Lechner, M. D.; Tshmel, A.

doi:10.1021/ma034139g

Cited by 9 publications

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“…As a result of using a procedure for breaking down asymmetry reflections into two separate Gaussian components [13,16], it was found that the overall profile of the reflection is in good agreement with the experimentally observed profile. The calculated parameters of both components for reflection [200] are shown in Table 1.…”

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confidence: 68%

“…A more detailed analysis of previously obtained x-ray diffraction data showed [13,[15][16]] that equatorial reflections [110] and [200] exhibit asymmetry. The barely perceptible asymmetry in the x-ray pattern of the gel becomes important when the solvent is eliminated (Fig.…”

mentioning

confidence: 99%

“…In contrast to the LAXD method, Raman spectroscopy in LAM regions provides information on the length distribution functions of all SCS F(L) not obligatorily contained in the crystalline phase [13,[15][16][17]. The F(L) for the gel and xerogel are shown in Fig.…”

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Structural Transitions in Manufacture of High-Strength Polyethylene Fibres by the Gel-Technology Method

et al. 2005

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The creation of fibres from flexible-and rigid-chain polymers with mechanical indexes close to the theoretically possible is an important problem in the physical chemistry and technology of polymers. The development of the gel-technology method [1,2] at the Dutch company DSM, which allows increasing the strength of fibres made of flexible-chain polymers by an order of magnitude, should be considered an impressive step toward solving this problem. Conversion of the solution into a gel was the key stage in obtaining strong fibres. After DSM, the gel-technology method was successfully implemented by other foreign and domestic companies [3,4], and fibres were made in laboratory conditions from ultrahigh-molecular-weight polyethylene (UHMWPE), whose mechanical properties are close to the theoretical values. It was predicted that total realization of the strength and elastic properties of fibres from flexible-chain polymers would not only lead to significant savings of material and energy resources but also to the creation of a new class of construction materials. A further increase in the mechanical indexes of these fibres will only be possible after a comprehensive study and purposeful formation of the gel structure and intermediate products in all stages of the manufacturing process.We conducted a comprehensive study of the structure of UHMWPE in the basic process stages of their manufacture from the initial gel to the final highly oriented state.We investigated UHMWPE with a molecular weight of M w = 1.7⋅10 6 . The UHMWPE solutions and gels with a concentration of polymer under 5% were prepared using vaseline oil, decalin, and p-xylene as solvent and the method in [7,8]. Xerogel films (dry gels from which the solvent was eliminated) were made by evaporating the volatile solvent at room temperature or by eliminating nonvolatile solvent by repeatedly squeezing the gel between sheets of filter paper. The samples of UHMWPE fibres were spun by the gel-technology method on an experimental-industrial setup [4] from a spinning solution of the polymer in vaseline oil with a concentration of 3%. The fibre, consisting of 240 filaments, underwent orientation drawing in solvent medium at 125°C to a draw ratio of λ = 30. The solvent was washed off with hexane and the fibre underwent additional orientation drawing in air at 145°C.The mechanical tests were performed on an Instron-1122 tensile-testing machine in standard conditions. The largeangle x-ray diffraction analysis (LAXD) was performed on a STADI P STOE and CIE diffractometer using the Debye Scherer equationwhere L is the cross-sectional dimension of the crystallite; K = 0.94; θ [200] is the diffraction angle of peak [200]; β is the half-width of peak [200].

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Structural Transitions in Manufacture of High-Strength Polyethylene Fibres by the Gel-Technology Method

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“…At low λ, the folds of lamellar crystallites probably do not straighten, and lengthening of the fibre is basically due to straightening of chain segments binding adjacent microcrystallites in the gel fibre [9]. The structural model of the physical UHMPE gel that we used in the interpretation was taken from [11]. The only melting peak in the thermogram (T 1 ) at small λ should be assigned to crystallites in folded chains (FCC).…”

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The structure of high-strength ultrahigh-molecular-weight polyethylene fibres fabricated by the gel-spinning method

et al. 2006

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In orientation drawing of UHMPE (ultrahigh-molecular-weight polyethylene) fibres, conformational rearrangements take place that enrich the conformation set of the polymer with T-isomers and impoverish it in G-isomers. The basic increase in the orientation of T-isomers is observed in the initial stages of drawing. In orientation drawing of UHMPE gel fibre, no significant increase was found in the concentration of molecular breaks, a necessary condition for effective strengthening of the fibre. Two types of crystallites (crystallites in folded and straightened chains) and a mesophase were found in samples of multifilament UHMPE fibres. There is a smooth transition from the structure of the foldedchain crystallite (FCC) type to a structure of the straightened-chain crystallite (SCC) type with an increase in the draw ratio due to formation of a rigid amorphous phase of straightened segments of the polymer chains.One of the main problems of polymer technology is to develop new and to improve existing methods of obtaining polymeric materials with extreme properties, particularly with high strength indexes. Gel spinning is currently used as the most effective and industrially feasible method of strengthening flexible-chain polymers [1,2]. It is possible to increase the strength of ultrahighmolecular-weight polyethylene (UHMPE) fibres by one order of magnitude in the stage of orientation drawing of spun gel fibres (the most important stage of gel spinning). However, the strength values attained are no greater than 10% of the theoretical limit [3]. It is important to study the rearrangement of the molecular and supramolecular structure of the polymer that take place during drawing and to establish their correlation with the mechanical properties for further orientation strengthening of fibres.We investigated the effect of orientation drawing on the structure of UHMPE fibres obtained by gel spinning and their elastic-strength properties. Comprehensive studies were conducted with such physical methods as Fourier IR spectroscopy, wide-angle x-ray diffraction, differential scanning calorimetry, and mechanical tests.We studied multifilament fibres (280 filaments) made from UHMPE with a molecular weight of M w = 1.9⋅10 6 drawn at different ratios and at different temperatures. The fibres were fabricated from a 3% spinning solution of UHMPE in paraffin oil in the conditions of the experimental setup at the All-Russian Scientific-Research Institute of Synthetic Fibres [4]. Drawing of the fibres was divided into three stages. The fibre was initially drawn at a temperature of 110°C to ratio λ = 3. In the second stage, after shrinkage, the fibre underwent one-stage thermal orientation drawing at 125-128°C. Both drawing stages were conducted in solvent medium. The third drawing stage was conducted in air at 140-145°C.The IR spectra of filament fibres laid in a monolayer parallel to each other on the frame holder were recorded in polarized light on an Equinox 55 Fourier IR spectrometer.The molecular structure and rearrangements in the...

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“…The crystalline nature of the chain fixers in PE gels was supported by the IR and Raman spectroscopic studies. 3 In this light, the properties of crystallites in gelled polymer could determine, to some extent, the capability of the given gel solution to yield high performance fibers after a routine drawing process. In this communication, the characteristics of crystalline substance in a series of xerogels obtained from the powders of ultra-high-molecular-weight PE (UHMW PE) with different technological prehistory were studied with the help of the low-frequency Raman spectroscopy, which provides the information on the length distribution of straight chain segments (SCS) in linear polymers.…”

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The straight‐chain segment length distribution in xerogels of UHMWPE, which provide high drawability of gel‐derived fibers

Пахомов

Galitsyn

Khizhnyak

et al. 2007

J of Applied Polymer Sci

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A series of ultra-high-molecular-weight reactor powders with different technological prehistory were utilized for obtaining fibers through the gel technology. The fibers prepared from some powders exhibited high draw ratios and good mechanical properties (Young's modulus and tensile stress) but other powders yielded fibers of very low drawability. The low-frequency Raman study revealed that the straight-chain-segment (SCS) length distributions in dried gels prepared from powders of ''drawable'' group are bimodal, while the gels issued from powders unsuitable for fiber drawing have unimodal length distributions of SCS.

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Gel-to-Solid Transition in Polyethylene from the Viewpoint of the Crystallization Process

Cited by 9 publications

References 14 publications

Structural Transitions in Manufacture of High-Strength Polyethylene Fibres by the Gel-Technology Method

Structural Transitions in Manufacture of High-Strength Polyethylene Fibres by the Gel-Technology Method

The structure of high-strength ultrahigh-molecular-weight polyethylene fibres fabricated by the gel-spinning method

The straight‐chain segment length distribution in xerogels of UHMWPE, which provide high drawability of gel‐derived fibers

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