It was shown that in treating PET fibre materials with a solution of ultradisperse, low-molecular-weight polytetrafluoroethylene in supercritical carbon dioxide, an ultrathin layer of fluoropolymer that gives the fabric a high degree of water repellency is formed on the surface.Due to the high demand for water-repellent textile materials for industrial and household applications, the problem of manufacturing stable and strong water-repellent coatings on widely used poly(ethylene terephthalate) (PET) materials is pressing. Despite the hydrophoby of PET fibres, the textile materials made from them cannot retain drops of liquid on their surface. Liquid instantaneously passes through the fabric due to forces of capillary suction of the complex fibres. PET materials have surface energy which is excess for the liquids in contact with them during use.To give PET textile materials stable unwettability, their surface energy must be significantly reduced. To do this, it is necessary to apply a substance whose hydrophobic sections are oriented to the outside area on each fibre without overlapping the micropores of the textile. A new outer surface with low surface energy is formed in this way.Water repellents are used in practice to manufacture fabrics with water-repellent properties, and effective textile auxiliaries based on fluorinated hydrocarbons are very popular [1]. However, the effect obtained with these preparations is not sufficiently stable, especially on synthetic fabrics. This is because the preparations based on fluorinated hydrocarbons are insoluble in water and are thus applied from emulsions and dispersions. They form weakly bound, thick, condensed layers on the surface of synthetic fibres which are easily washed off in laundering and dry cleaning and are rubbed off as the fabric is used.Attempts have been made to improve the composition of the product to eliminate this drawback. In particular, one of the world leaders in developing and manufacturing products for the textile chemistry, the Swiss firm Clariant, is offering a new series of fluorine-containing products for hydro-and oleophobic finishing -the Nuva group of products [2]. These products ensure that fabrics of different composition are given excellent oil-and water-repellent properties. However, the products are used in high concentrations (for synthetics, 10-30 g/liter) [2] and are very expensive. In addition, the inadequate resistance of the effect attained to the effects of use persist, since the water repellents are also applied from emulsions or dispersions.This drawback can be eliminated by applying a water-repellent substance from natural solution. In this case, it is no longer necessary to use specially synthesized complex products based on polymer compositions of fluorinated hydrocarbons containing emulsifiers. An additional advantage of stopping use of complex water-repellent products containing cationactive emulsifiers is reducing the tendency of the water-repellent textile material toward dry soiling. An industrially manufactured fluori...

Comparative analysis of the characteristics of supramolecular structures of dry and swollen cotton fibers makes it possible to differentiate structural regions accessible to water. The revealed features of water desorption from cotton cellulose (exceptionally low rates at the final stages, presence of residual moisture) are related to the removal of water, which is localized in the regions of the crystalline phase disorganized upon drying. The fact of incomplete moisture removal from cotton fibers at T < 325 K is interpreted from the stand point of the frozen molecular mobility in the microsurroundings of sorption sites, which are located at the defects of crystallites, at the final stage of the desorption process. A marked contribution from the recrystal lization of disorganized regions in the surface layer of crystallites to the thermal effect of the interaction between water and cotton cellulose at low water content is established.

547.458.81X-ray structural analysis showed that both the crystallite content and the degree of perfection of their surface layer increase during dampening of cotton cellulose. The maximum structural ordering of cellulose is attained at a fibre moisture content ≥14.8%. The determining role of the absorption mechanism of dissolution of water in amorphous regions of cellulose is confirmed by a quantitative estimation of the X-ray diffuse scattering parameters for cotton with different moisture contents.In contrast to most natural and chemical fibres, the breaking load of cotton increases significantly in dampening, which is usually attributed to the morphological features of its structure [1]. A hypothesis was also advanced concerning the correlation of this event with the supramolecular structure of cotton fibres [2]. This hypothesis is in agreement with the quantitative x-ray diffraction data on the effect of moisture on the crystalline [3] and amorphous [4] phases of cotton cellulose. For this reason, it is useful to examine the structural transformations in cotton cellulose during sorption of water within the framework of the unique amorphous-crystalline structure of the polymer. Our study analyzed the effect of the moisture content of cotton fibres on the x-ray diffraction parameters of crystallite regions and the amorphous phase of cellulose.We investigated scoured and bleached cotton cloth with a moisture content (ω) of 0 to 19.4%, attained by holding the sample at 20°C in desiccators above solutions of sulfuric acid of different concentration.The x-ray structural analysis was conducted on a DRON-3 diffractometer using CuKα radiation separated by balanced Ni and Co filters. The transillumination scheme with simultaneous rotation of sample and detector was used. The flat sample placed in a hermetically sealed cell was prepared by pressing disks of fabric cut out with a template at a pressure of 400 MPa, which ensured maximum orientation of the fibres in the preparation and stability of its shape [5]. The sample scattering parameters were quantitatively estimated according to [4,6] using the diffractometers computer system. The diffraction characteristics were normalized with the scattering intensity of an external standard and the optical densities of the sample and the cellulose component [3,4].The curves of the normalized x-ray scattering intensity I n s (2θ) for dry and dampened (ω = 19.4%) cotton fibres are shown in Fig. 1 as an example.The integral scattering value in the range of ∆2θ = 18.5-2.65°, corresponding to the intensity distribution for maximum reflection 002, was used in assessing the changes in the crystalline phase of the fibres as a result of dampening (see Fig. 1). The intensity of reflections 002 and 040 caused by the transverse and longitudinal ordering of cellulose I were also analyzed [5]. The values of the halfwidth of these reflections, determined with consideration of the instrumental factor [3], were used to calculate the longitudinal and transverse crystallite size.Separation of dif...

It is shown that the important change in the x-ray diffraction parameters in preparation of compact products from microcrystalline cellulose and ground cotton fibres by pressing is not due to the amorphous phase of cellulose. A method for determining the degree of crystallinity of cellulose in anisotropic materials using an external standard that ensures spherical scattering symmetry is substantiated. The applicability of the proposed approach for estimating the degree of crystallinity of cellulose fibres directly in fabrics, which reduces the duration of the experimental procedures by 3-4 times, is demonstrated.Pressing is used to increase the compactness and stability of samples for x-ray diffraction analysis of cellulose materials [1][2][3][4]. A drawback of this method is the dependence of the diffraction properties on the type and conditions of formation of the samples (fibre, fabric) due to the features of the texture formed [2,4]. The necessity and possibility of taking this factor into account are valid in solving the problem of determining the polymorphous composition of cotton materials [4]. We will examine the possibility of x-ray diffraction estimation of the degree of crystallinity of cellulose materials of different anisotropy prepared by pressing in different conditions.Bleached cotton fabric and fibres separated from the fabric and ground into 0.2-0.5 mm fragments were investigated. Microcrystalline cellulose (MCC) obtained by hydrolysis of cotton fibres in 2.5 N solution of HCl at 100°C and powdered amylopectin of the same chemical composition as cellulose were also used. Flat samples of constant diameter were prepared by pressing in the 0 to 400 MPa pressure range in a special mold. The fabric was also used in the form of a set of disks cut with a template. In view of the effect of the moisture content of the cellulose fibres on the diffraction parameters [5,6], the samples were dried at 105°C. The x-ray diffraction analysis was conducted on a DRON-3 diffractometer with the transillumination method with simultaneous rotation of the detector and the sample (θ -2θ scheme), which made it possible to consider the factors that affect absorption and scattering by the samples. CuKα radiation separated by balanced Ni and Co filters was used. The samples were placed in a hermetically sealed cell with polyester film windows and placed in a holder that made it possible to average the diffraction intensity by rotating the objects. The background was taken into account by separately scanning an empty cell with the sample placed in front of the detector.The intensity of scattering by the samples I sam (2θ) at diffraction angles 2θ was determined with consideration of the background and use of differential filters based on the equations from [6]. The integral value of scattering by the samples A sam in the given range of angles ∆2θ was found with the equationwhere A exp t(∆2θ) is the experimental integral value of scattering by the sample, pulses; A b (∆2θ) is the integral value of the background, pulse.Ivanov...

Hydrostatic weighing of a polymer in an immersion liquid using low-density polyethylene as an example was used to show that a condition for the lack of recrystallization of partially crystalline polymers upon annealing is the attainment at this temperature of thermomechanical equilibrium that determines the ratio of the amounts of macromolecule elementary units existing in amorphous and crystalline regions during the crystallization of these polymers. A basis was found for the viewpoint that the Gibbs-Thomson equation is applicable only for estimating the dimensions of the last (not bonded to each other by connecting chains) crystallites disappearing at the true melting point.It is commonly thought in discussing crystallization processes of polymers with flexible chains from the melt, their additional crystallization (melting-recrystallization) during annealing, and complete melting [1-8] that these polymers are biphasic (crystalline and amorphous phases) and thermodynamically non-equilibrated (metastable).The experimentally observed manifestations of the metastability of partially crystalline polymers are: -a lower melting point (mp) than the equilibrium value ( 0 m T ) characteristic of ideal crystals; -a dependence of the mp on the heating rate and the thermal history of the sample; -additional spontaneous crystallization with a decrease of the glassification temperature of amorphous regions to the ambient temperature.Additional crystallization was clearly evident during successive stepwise heating of a partially crystalline polymer undergoing hydrostatic weighing in an immersion liquid. Additional crystallization of low-density polyethylene (LDPE) pressed at 160°C and crystallized in air at room temperature (mp = 111.2 ± 0.4°C) was distinctly observed in the range 58.5-110.2°C with such a heating regime [9]. Apparently only amorphization occurred in the range 29.3-58.5°C. Anyway, preliminary storage of the sample in a differential scanning calorimeter cell for 1 h at 40°C was accompanied by a decrease of its heat of fusion (ΔH m ) by 6% [glassification temperature (T g ) of this LDPE sample was about -53°C].Strictly speaking, these results were expected and agreed completely with existing concepts about the thermal behavior of partially crystalline polymers. However, the problem is that if the postulates of Gibbs regarding phase equilibria are strictly adhered to [10], then such polymers should be viewed as monophasic microheterogeneous metastable liquids in which the ratio between the amount of macromolecule elementary units located in the amorphous regions and crystallites is determined by the thermomechanical equilibrium conditions [11].Such treatment of the monophasic state of partially crystalline polymers differs in principle from that proposed earlier [3, p. 326] in that the amorphization process of such polymer liquids is considered to be a first-order phase transition complicated by a three-dimensional strain deformation relative to regions with long-range three-dimensional ordering in the space aro...