Effect of Water on the Physicomechanical Properties of Composites Containing Low-Density Polyethylene and Linen Yarn Production Waste

The effect of the amount of absorbed water on the physicomechanical indices (tensile modulus and tensile strength) of composites based on low-density polyethylene (LDPE) and linen yarn production waste (LW), both with and without coupling agents (stearic acid - SA and diphenylmetane diisocyanate - DIC), is studied. It is shown that the strength properties depend considerably on the time of water sorption and on the blend composition. The tensile strength decreases with increased amount of absorbed water (with increased time of exposure to distilled water) and with increased content of LW in the composite. Somewhat different results are obtained for systems containing SA and DIC modifiers. The modifiers, intensifying the interfacial interaction, retard the process of water sorption, therefore the drop in the strength indices is not so significant. Of special interest is the behavior of systems with DIC. In some cases, a slight increase in strength (after a two to five day exposure to water) is observed, which is probably caused by cross-linking of the free diisocyanate in the system under the action of moisture.     

Correlation between the Mechanical Properties and the Amount of Desorbed Water for Composites Based on Low-Density Polyethylene and Linen Yarn Production Waste

The effect of the amount of desorbed water on the mechanical properties of composites based on low-density polyethylene and linen yarn production waste (LW) is analyzed by statistical methods. It is shown that the amount of absorbed water decreases during the desorption process at room temperature both for specimens modified and unmodified with diphenylmethane diisocyanate (DIC.) The most sensitive to the action of water is the elastic modulus, which decreases considerably under the effect of water and is fully restored in the desorption process. The tensile strain also increases with the amount of absorbed water. It is found that the elastic modulus of the unmodified composite correlates linearly with the amount of desorbed water. Between the amount of desorbed water and the tensile strain, as well the specific work of deformation, a negative linear correlation is revealed. After water desorption, all strength and deformation characteristics of both the modified and unmodified composites are fully recovered.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 515–524, July–August, 2005.     

Correlation between the mechanical properties and the amount of desorbed water for composites based on a recycled low-density polyethylene and linen yarn production waste

The effect of the amount of sorbed water on the mechanical properties (tensile modulus, tensile strength, unit work of fracture, and characteristic strains) of composites based on a recycled low-density polyethylene, both unmodified and modified with diphenylmethane diisocyanate (DIC), is an a lyzed by statistical methods. The results of tensile tests are found to depend on the amount of sorbed water considerably. The elastic modulus, the unit work of fracture, and the characteristic strains correlate linearly with the amount of water. It is found that the elastic modulus drops after the sorption of water, but then, during the desorption process, it is restored gradually and reaches its initial value after a 30-day drying. This is explained by the plasticizing effect of water on composite materials containing hydrophilic natural fibers. DIC improves the interfacial interaction of the fiber-matrix interface and slows down the desorption of water. The investigations of the main deformational and strength characteristics of the unmodified and modified systems showed that the ad verse effect of water completely disappeared after a 30-day drying. The same conclusion, with a 95% probability, can be drawn from the results of an analysis of variance (ANOVA). __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 5, pp. 626–638, September–October, 2007.     

Physicomechanical properties of composites from recycled polyethylene and linen yarn production wastes

The possibilities of utilizing wastes of linen thread production (chaffs, spinning and roving losses) in recycled polyolefin composites have been investigated. The wastes were mixed with recycled polyethylenes (produced from domestic and industrial film production wastes). The physicomechanical properties (tensile strength, bending and tensile moduli, and water resistance) and the fluidity (melt flow-behavior index) for systems with a different filler content are estimated. Almost all the composite materials obtained have satisfactory fluidity (melt flow-behavior index is not lower than 0.07–0.15 dg/min). For all types of the composites, a slight increase in tensile strength and a considerable increase (3–7 times) in bending and tensile moduli were observed. The water resistance of the composites decreased with an increase in the filler content. The modification of filled systems with diisocyanates (diphenylmethane diisocyanate) improved the useful properties and water resistance of all the composites investigated.     

Physicomechanical properties of composites from recycled polyethylene and linen yarn production wastes

The possibilities of utilizing wastes of linen thread production (chaffs, spinning and roving losses) in recycled polyolefin composites have been investigated. The wastes were mixed with recycled polyethylenes (produced from domestic and industrial film production wastes). The physicomechanical properties (tensile strength, bending and tensile moduli, and water resistance) and the fluidity (melt flow-behavior index) for systems with a different filler content are estimated. Almost all the composite materials obtained have satisfactory fluidity (melt flow-behavior index is not lower than 0.07–0.15 dg/min). For all types of the composites, a slight increase in tensile strength and a considerable increase (3–7 times) in bending and tensile moduli were observed. The water resistance of the composites decreased with an increase in the filler content. The modification of filled systems with diisocyanates (diphenylmethane diisocyanate) improved the useful properties and water resistance of all the composites investigated.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 2, pp. 199–210, March–April, 1999.     

The influence of water sorption-desorption cycles on the mechanical properties of composites based on recycled polyolefine and linen yarn production waste

The effect of water on the mechanical properties (tensile modulus, ultimate tensile strength, tensile strain, and specific work at break) of both chemically treated and untreated composites based on a recycled low-density polyethylene and linen yarn production waste is analyzed. It is found that three water sorption-desorption cycles change the tensile properties of both the materials irreversibly. This effect is considered as the result of partial fracture of the fiber-matrix interface. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 6, pp. 839–848, November–December, 2007.     

Evaluation of Deformation and Strength Characteristics of Composites Based on Low-Density Polyethylene and Linen Yarn Production Waste by the Methods of Mathematical Statistics

The possibilities of using various methods of mathematical statistics for processing and analyzing the results of deformation and strength tests on composites made from a low-density polyethylene and linen yarn production waste are evaluated. The hypothesis that the experimental strength data agree with the Gaussian distribution is examined by the Shapiro–Wilk test (W-test.) It is shown that the Gaussian distribution, both for systems unmodified and modified with diphenylmethane diisocyanate (DIC), is valid only for two parameters: the maximum tensile strength _max and the elastic modulus E _t. For the other parameters (the relative elongation _max corresponding to _max, the specific total work of failure A _b), and the specific work of failure to the tensile strength A _max), a non-Gaussian distribution is observed. An analysis of measurements for different specimens by the Bartlett test shows that the E _t data have equal variances for both systems (with and without DIC), but for the system containing DIC, the _max data have different variances. A two-factor ANOVA analysis reveals that DIC considerably affects the tensile strength and modulus of composites, but the influence of test conditions is a statistically significant factor only for the modulus. The coefficient of variation is considerably lower for _max than for E _t and can be used as a quantitative measure for the degree of heterogeneity of the composites investigated.     

Effect of the composition and concentration of fibrous wastes from linen yarn production on the physicomechanical properties of polyolefin composites

An analysis is made of the feasibility of using wastes from the production of linen yarm (scutch, spinning and carding refuse) to modify low-density polyethylene. The effect of the composition and concentration of wastes on the processing properties (melt index), physicomechanical indices (tensile strength, elastic modulus in bending), and water resistance of composites based on low-density polyethylene is studied. It is found that the melt index decreases with an increase in the content of filler and that even a composite with a high filler content (40–50% by weight) maintains values of 0.2–0.3 g/10 min. The elastic modulus in bending increases with an increase in the content of waste, regardless of the nature of the latter. Tensile strength increases slightly and depends on the choice of filler. This result, combined with the reducation in the scatter of values of elastic modulus with an increase in filler concentration, is an indicator of the relatively high degree of heterogeneity of the systems that were studied. The water resistance of the composites decreases with an increase in filleer content. To reduce the heterogeneity of the systems, mixing should be intensified and modifiers such as stearic acid and polyisocyanates should be added.Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 3, pp. 408–416, May–June, 1997.     

Strength and deformation characteristics of polymer blend films obtained from water systems

The relationship between the tensile strength and deformation characteristics, composition, and structural organization of films obtained by casting of two-component water-based system blends — a solution of the rigid partly crystalline polymer polyvinyl alcohol (PVA) and an emulsion of the compliant amorphous polymer polyvinyl acetate (PVAc) — has been investigated. The aim of this investigation was to ascertain the possibility of obtaining film materials with increased deformability based on the biodegradable PVA. The composition dependences of the initial modulus of elasticity, the maximum stress, yield stress, the ultimate strength, the ultimate strain, and of the unit work of fracture and other characteristics of films have been analyzed. An analysis of the tensile true stress–strain curves of systems with volume fractions of PVA less than 0.5 points to their considerable orientation strengthening upon tension.     

Composites based on cellulose fiber nonwovens and a water soluble polymer 1. Structure and strength-deformation characteristics of cellulose fiber nonwovens and structural characteristics of the composites

The results of a study on the strength-deformation characteristics (tensile elastic modulus, ultimate strength, elongation at break, and punching and tearing strengths) of two kinds of cellulose fiber nonwovens (CFNs) with dissimilar void content and different geometrical parameters of cellulose fibers are discussed. The structural characteristics of composites prepared by impregnation with poly(vinyl alcohol) water solutions are analyzed, too. Composites with volume fractions of polymer up to 0.4% and volume fractions of voids up to 0.3% were prepared. Filling of voids by the polymer occurred without significant changes in the structure of CFNs. The fraction of closed voids increased with polymer content.     

Tensile strength of ABS/PA6 composites reinforced with HNO<Subscript>3</Subscript>-treated carbon fibers

In this study, an acrylonitrile-butadiene-styrene (ABS) terpolymer was reinforced with HNO₃-treated short carbon fibers (SCFs). The effects of SCF concentration on the tensile properties of the composites were examined. Increasing the SCF concentration in the ABS matrix from 10 to 30 wt.% raised its tensile strength and tensile modulus. To obtain a strong interaction at the fiber-matrix interface, polyamide-6 (PA6) at varying concentrations was introduced into the ABS/10 wt.% SCF composite. The incorporation and increasing the amount of PA6 in the ABS/PA6/SCF systems upgraded their tensile properties due to the improved adhesion at the fiber-matrix interface, which was confirmed by the growing tensile strength. These results were also supported by scanning electron micrographs of the ABS/PA6/SCF composites, which exhibited an enhanced adhesion between the SCFs and the ABS/PA6 matrix.     

Physicomechanical Properties of One-Dimensional Periodic Structures by Transmission of Laser-Excited Wide-Band Acoustic Pulses

The strength-deformation characteristics of a low-density polyethylene filled with cellulose-containing products, such as microcrystalline cellulose Thermocell, pinewood grinding dust and sawdust, and technical Thermocell obtained by a thermocatalytic method from pinewood raw materials are studied. The effect of the type of the filler and its content in the composite on the tensile strength, relative elongation, and work of failure in tension is determined. The water sorption and change in the strength-deformation characteristics of the composites during water sorption and desorption are also studied. It is found that the thermocatalytic treatment of cellulose-containing fillers makes it possible to increase the tensile strength of composites and to decrease the strength drop caused by water sorption.     

Effect of water sorption on some mechanical parameters of composite systems based on low-density polyethylene and microcrystalline cellulose

Strength-deformation characteristics of low-density polyethylene filled with microcrystalline cellulose Thermocell as a function of the TC content (up to 0.7 parts by weight) are studied. Characteristics such as elastic modulus, relative elongation at break, ultimate strength, and work of failure are determined. Water sorption and change in the size and strength-deformation characteristics of composite specimens during exposure to boiling water (560 min) are also studied. It is shown that with greater filler content it is possible to increase the strength-deformation characteristics of LDPE, such as elastic modulus and tensile strength. The growth of the ultimate strength is associated with the formation of a specific filler framework with increasing filler content. It is found that the main factors which cause a decrease in the elastic modulus and softening of the composite are failure of the filler framework as well as formation of stresses and voids during water sorption by the composite. It is demonstrated that the steady reproducibility of the composition, attainable high filling degrees, and ecological safety make Thermocell a promising filler for polyethylene.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 1, pp. 79–90, January–February, 1999.     

混凝土轴拉加卸载随机损伤模型的建立与试验验证

为了分析及深入探讨混凝土在受拉加载及卸载情况下的力学特性,基于随机损伤本构关系提出了一种混凝土轴拉加卸载模型,推导出了混凝土加卸载的应力 应变关系表达式.为了印证理论表达式,进行了混凝土轴向拉伸及加卸载的试验研究,测得了混凝土的材料参数及其相应的轴拉加卸载应力-应变曲线.结合模型的计算结果,对混凝土的轴拉加卸载试验结果进行了对比分析,结果表明:混凝土轴拉加卸载模型能够预测混凝土的极限强度,同时能描述混凝土的强度软化、加载过程中的弹模折减及卸载后的塑性变形.     

Processing,structure, and mechanical properties of alumina-nanofilled polystyrene composites

Binary composites composed of polystyrene (PS) and a synthetic boehmite alumina were produced by using the water-mediated melt compounding (WMC) and direct melt compounding (DMC) techniques. The alumina particles were dispersed in water at ambient temperature. The aqueous alumina suspension was injected into molten PS in a twin-screw extruder to prepare reinforced polymer composites. The dispersion of the alumina was studied by transmission and scanning electron microcopy techniques (TEM and SEM, respectively). The mechanical and thermomechanical properties of the composites were determined by employing a dynamic-mechanical thermal analysis (DMTA) and short-time creep and uniaxial static tensile tests. It was found that the direct melt compounding of the alumina with PS resulted in microcomposites, whereas the water-mediated melt compounding technique gave rise to nanocomposites. The incorporation of alumina into the PS nanocomposites increased their stiffness, tensile strength, and creep resistance. However, the elongation of the PS nanocomposites at break was smaller than that of the PS microcomposites.     

On the mechanical and thermomechanical properties of low-density polyethylene/ethylene-α-octene copolymer blends

Blends of low-density polyethylene (LDPE) and ethylene-octene copolymer (EOC) were obtained. The effect of EOC content and absorbed radiation dose on the mechanical and thermomechanical properties of LDPE/EOC blends are investigated. Particular attention is given to a tensile stress-strain analysis and the “form-memory” effect of the blends. With growing LDPE content, the elastic modulus, the yield stress, and the thermorelaxation and residual stresses of the blends increase, but the ultimate elongation at break decreases, which is caused by the higher crystallinity of polyethylene. As a result of radiation-induced cross-linking, the elastic modulus, the yield stress (at a 1% strain), the ultimate yield strength, and the thermorelaxation and residual stresses increase, while the ultimate elongation at break and the melt flow-behavior index decrease, which is confirmed by the growing gel fraction in the blend. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 2, pp. 279–286, March–April, 2008.     

Strength of Unidirectional Composites under High Hydrostatic Pressures

The dependence of the strength properties of two unidirectional fibrous composites on high (up to 500 MPa) hydrostatic pressure has been studied experimentally. Ring specimens of epoxy carbon- and glass-fiber-reinforced plastics were tested in tension using half-disk devices. The tensile strength in the reinforcement direction increased with increase in the pressure up to 300 MPa. However, at a further increase in the pressure, this strength decreased. It was found that the failure mode of unidirectional composites depends on the magnitude of hydrostatic pressure. The failure shapes differed in the location of the failure zone and in the relative extent of longitudinal cracks in the specimens. At atmospheric pressure, the failure zone covered practically the whole volume of the specimens. With increased pressure, the failure zone became localized. At the highest pressures investigated, the failure was accompanied by the formation of a single crack across the reinforcement direction.     

三维四向编织复合材料刚度和强度的理论预测

以单胞模型为基础,将三维四向编织复合材料中相同走向的纤维束视为单向复合材料,利用桥联模型确定了单向复合材料的柔度矩阵,再将具有不同材料主向的单向复合材料的刚度矩阵通过体积平均,得到了三维四向编织复合材料的总体刚度矩阵,从而得到其工程弹性常数．然后,以单向复合材料为基础,基于等应变假设和桥联模型,确定出材料内各组分（纤维束和基体）的细观应力分布,且对纤维束采用Hoffman失效准则,对基体采用Mises失效准则,预报了三维四向编织复合材料的拉伸强度．     

Influence of Modifiers on the Physicomechanical Properties of Sawdust-Polyethylene Composites

Polymer-wood composites based on recycled polyethylene (RPE) are investigated. Dispersed alder sawdust was utilized as a filler. To improve the compatibility between the nonpolar matrix and the polar wood fibers as a reinforcement, two types of modifiers were used, which differed in their chemical nature and mechanical interaction with the constituents of the composites. The modifiers of the first type (paraffin and OP) improved the dispersibility of sawdust (SD), and those of the second type (Exxelor 1015 and OREVAC) contained groups of maleic anhydride, which interacted with the OH-groups of SD. The effect of the modifiers on the moisture sorption by SD, the dispersibility of the filler in the matrix, and the strength characteristics (ultimate strengths and moduli in tension and bending) of dry and moist RPE–SD composites and on their moisture sorption is estimated. The best results were obtained for the composites modified with paraffin, which is due to the more efficient employment of the strength and rigidity of well-dispersed SD fibers. In their strength characteristics, the RPE-based composites investigated are comparable to composites based on low-density polyethylene.     

Effects of temperature and moisture on the mechanical properties of polyester resin in tension

The effect of environment on the physical and mechanical properties of composite materials in some cases is determined by the environmental sensitivity of the binder. The results of experimental investigation of the deformability and strength of polyester resin, widely used as a binder in composites, upon the action of stationary and quasi-stationary loads, temperatures, and moisture are presented. The ranges of acceptable values of these services factors are determined. The elastic modulus and tensile strength of the material are obtained from quasi-static tests. The viscoelastic behavior of the resin is investigated in creep tests. From the results of a short-term experiment with stepwise loading up to failure, it is found that the creep of specimens with a moisture content of 0.14% can be described by a linear viscoelastic model for stresses up to 20 MPa (two thirds of the strength). The action of single loading impulses is summarized according to the Boltzmann superposition principle. The temperature and absorbed moisture are considered as factors accelerating the relaxation processes in the material. The creep activation under the action of these factors is described using the methods of time-temperature and time-moisture equivalence. The results of short-term creep tests allow us to determine the relaxation characteristics of the material in stationary conditions. The long-term creep under close-to-service conditions is predicted using these data and quite good agreement with the control test is obtained. The sensitivity of the material characteristics (strength, elastic modulus, and creep strain) to the action of temperature and moisture is estimated. The creep strain is most sensitive to the action of environmental factors. For a fully saturated material (moisture content 1.64 wt.%), after one hour creep, this strain four times exceeds that of a dry one. The same growth in deformability is caused by an 18°C increase in temperature. A quantitative comparison of the characteristics of polyester and epoxy resins allows us to choose the binder for composites and to estimate the expected environmental effect. Presented at the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 3, pp. 395–406, May–June, 2000.