Three epoxy binders formulated using epoxy resin ED-20 and cold-curing (Etal-23Kh), hot-curing (IMTHPA) and warm-curing (KhT-152B) agents were studied herein. Rheological, mechanical and thermomechanical behaviors of the binders were examined. All the three binders were found to exhibit a low initial viscosity of 0.5 − 1.4 Pa∙s and retain rheological properties for 3 − 5 h at 23 ⁰C (Etal-23Kh) and 40 − 60 ⁰C (IMTHPA, KhT-152B) required for composite fabrication by the wet-filament winding process. The cured binder specimens had comparable tensile strengths of 62 − 72 MPa. The glass transition temperature increased with increasing admissible temperature at which the binders underwent polymerization. For instance, the glass transition temperature was 80 − 82 ⁰C for the cold-curing binder, 111 − 113 ⁰C for the warm-curing one, and 132 − 134 ⁰C for the hot-cuing one. All the three binder formulations were employed to fabricate unidirectional basalt fiber-reinforced plastics (BFRPs). All the binders showed close elastic moduli of 40 − 43 GPa for the BFRPs. The BFRP based on the EDI binder with the IMTHPA hot-curing agent had a higher strength value of 1571 MPa and ultimate strain value of 4.16

The paper presents the results of comparative tests of unidirectional basalt plastics. All tests are performed using three different methods, with their advantages and disadvantages being identified. A comparative analysis of the obtained experimental data is carried out including the assessment of strength, Young's modulus, and ultimate fracture strain. The most accurate values of strength characteristics (a=1571 MPa, E=42363 MPa) are obtained for samples manufactured by following the RF patent No. 2597811. These values are the closest to the theoretical ones calculated using the mixture rule and proper ratio of components. The implementation coefficients for characteristics of a reinforced filler and a binder of unidirectional samples produced in laboratory conditions are 0.7 for strength and 0.85 for Young’s modulus, calculated theoretically. Test results for the GOST 25.603-82 ring samples show almost twofold spread of obtained characteristics (strength varies from 500 to 1076 MPa, Young's modulus cannot be determined due to the method complexity). The GOST 33349-2015 samples have uneven thickness along their length and demonstrate unstable strength characteristics (a=1130 MPa, E=33052 MPa). They are lower than the characteristics of the RF patent No. 2597811 samples.

The DSC method revealed endothermic effects (–613.9 J/g) during gypsum dihydrate heating associated with the heat absorption during the release of crystalline hydrate water in the range of 100–250°C during the heating process. Mass losses during water evaporation were determined by TGA and amount of up to 20

Rheological, physical-mechanical and thermomechanical properties of binders based on ED-20 epoxy resin with Ethal-45M amine hardener and additives of Cardura E10P glycidyl ether from 5 to 50 wt.% as a diluent have been studied. As the Cardura E10P content increases, the dynamic viscosity of the binder decreases significantly and the gel time increases. The tensile strength of cured samples decreases from 49 MPa to 12 MPa with an increase in the Cardura E10P content from 5 to 30 weight parts, the deformability increases from 14 to 38%, and the glass transition temperature decreases from 67°C to 49°C.

Green and renewable materials are becoming promising worldwide. Here, we compared morphological and mechanical strength characteristics of natural plant-based bast fibers (flax, hemp and nettle) with those of synthesized fibers (glass, basalt, carbon, polyacrylonitrile (PAN), polycaproamide (PCA) and viscose). The industrial bast fibers from hemp and nettle were extracted by chemical treatment with a sodium carbonate solution. The natural fibers were comparable in size to the synthetic ones. The PCA fibers had the largest diameter of 23–28 µm. The carbon monofiber had the lowest diameter of 7–8 µm. The dimension of the natural elementary fibers was 10–25 µm. The natural fibers had a better interfacial bonding to an epoxy matrix than PCA. Moreover, the specific strength of the unimpregnated and epoxy-impregnated fibers was determined. The natural fibers were superior in strength performance to some of synthetic fibers (viscose), while the specific strength of the impregnated flax fiber was commensurate with that of the impregnated PAN and PCA fibers. The specific strength of the flax and hemp fibers once impregnated with the matrix increased four- and twofold, respectively. The impregnated flax fibers exhibited the best mechanical strength behavior among the hemp and nettle bast fibers. The natural fibers are biodegradable, have a low density, and are more eco-benign than the mineral fibers. The selected natural fibers can be used to fabricate composites therefrom.

Описан автоматизированный процесс изготовления образцов однонаправленных композитов на основе волокон различной природы (минеральных, химических, растительных) методом намотки. Испытания образцов проведены автоматизированным методом продольного изгиба с определением прочности, модуля упругости и предельной деформации при разрушении, с автоматической обработкой результатов и выводом протокола испытаний. Образцы углепластика имеют высокий модуль упругости 67 ГПа при низкой деформации 1,67 %, образцы композитов из полиакрилонитрильных нитей имеют высокую деформацию 6,35 % и низкий модуль упругости 4,8 ГПа. Прочность 1000-1200 МПа и модуль упругости 33-35 ГПа базальто- и стеклопластика сопоставимы. Образцы композитов на основе лубяных волокон конопли и льна сопоставимы с композитами из волокон ПАН по значениям прочности 100-127 МПа и модуля упругости 4,7-5,6 ГПа. Показана принципиальная возможность автоматизированного изготовления однонаправленных образцов композитов методом намотки и чувствительность автоматизированного метода испытаний продольным изгибом к упруго-прочным свойствам композитов из разных видов волокон. An automated process for manufacturing samples of unidirectional composites based on fibers of various natures (mineral, chemical, plant) using the winding method is described. The samples were tested using an automated longitudinal bending method to determine strength, elastic modulus and ultimate strain at failure, with automatic processing of the results and output of a test report. CFRP samples have a high elastic modulus of 67 GPa with a low deformation of 1.67%, samples of composites made from polyacrylonitrile yarns have a high deformation of 6.35% and a low elastic modulus of 4.8 GPa. The strength of 1000-1200 MPa and elastic modulus of 33-35 GPa of basalt and fiberglass are comparable. Samples of composites based on hemp and flax bast fibers are comparable to composites made from PAN fibers in terms of strength values of 100-127 MPa and elastic modulus of 4.7-5.6 GPa. The fundamental possibility of automated production of unidirectional composite samples by the winding method and the sensitivity of the automated longitudinal bending test method to the elastic-strength properties of composites from different types of fibers are shown.

The rheological, physicomechanical, and thermomechanical properties of the binders based on an ED-20 epoxy resin and KhT-152 B, Etal-450, and Iso-MTHPA curing agents have been studied. The rheological properties of binders are practically comparable. The KhT-152 B binder-based compound exhibited the highest durability. The Iso-MTHPA based binder exhibits the highest tensile strength among all studied compounds. The studied binders are comparable in terms of thermomechanical properties, and their glass-transition temperature is 100–110°C.

The article concerns with the assessment of the thermal performance of a facade system using fastening elements made of glass fiber-reinforced plastic (GFRP). The article analyses the efficiency of the technical solution based on fibreglass plastic in comparison with its metal-based counterparts. We present theoretical calculation data and graphs of thermal fields, calculate heat losses through point and linear thermotechnical inhomogeneities. As opposed to a steel spacer assembly with a coefficient of thermal homogeneity up to 0.82, such a design coefficient for a fibreglass element (0.99) is close to 1.0. Herein, the GFRP fastening elements demonstrated practical efficiency when used in real modern facade building structures: the thermal insulation thickness for GFRP was 130 mm, while that for the steel elements was 160 mm when applied in the facade fixing system.

The chemical resistance of binders based on epoxy resins and IMTHFA, KhT-152 B, and ETAL-450 hardeners is studied. A binder based on ED-20 and IMTHFA+UP606/2 has the best chemical resistance to nitric acid. The composite based on the ED-20 and KhT-152 B shows the highest chemical resistance to sodium hydroxide solution. The binder based on ETAL-370 and ETAL-450 exhibits a better chemical resistance to water environment.

Comparative tests of the following fibers are conducted under the same conditions: mineral (basalt, glass), carbon, chemical (polycaproamide, polyacrylonitrile, viscose fibers), and vegetable (bast fibers of linen, hemp, nettle). The diameter of a monofiber, linear density, breaking strength of a roving (a bundle of fibers) and microplastics, breaking tenacity, and gain ratio are assessed. Glass and basalt fibers have the highest linear density of 1200–2500 tex; carbon, 378 tex; chemical, 183 tex (except for PANF, which has 826 tex); and bast vegetable fibers, 440–630 tex. The breaking tenacity for glass rovings and basalt rovings is comparable of 240–264 mN/tex and is the highest of 597 mN/tex for carbon rovings; the gain ratio is 2–2.25. For chemical fibers, the breaking tenacity is 282–323 mN/tex (92 mN/tex in viscose ones) and the gain ratio is 0.5–0.9. Of vegetable fibers, the highest breaking strength of 93–102 mN/tex is in the fibers of linen and hemp, which exceeds this parameter for a viscose fiber; the gain ratio is 1.6 in hemp and 4.39 in linen. In fibers of nettle, the results are the lowest among vegetable fibers.

Современные мировые тенденции развития полимерных композиционных материалов направлены на уменьшение негативного воздействия на окружающую среду при изготовлении, эксплуатации и утилизации таких материалов. В этом плане наиболее перспективными являются биокомпозиты, армированные растительными волокнами. Благодаря экологичности растительных волокон, их малому весу в сочетании с высокими механическими свойствами и биоразлагаемостью, композиты на их основе уже находят применение в автомобилестроении, строительстве и других отраслях промышленности. В работе исследованы образцы крапивы двудомной, собранные в Республике Алтай в августе 2022 года. Целью данной работы являлось выделение и исследование структуры технических лубяных волокон крапивы в продольном и поперечном направлении, определение геометрических и физико-механических характеристик выделенных волокон. Структуру поперечного среза стебля крапивы и выделенных лубяных волокон исследовали с помощью электронного микроскопа. На фотоснимках стебля четко выделяются три зоны: наружный покрывной слой, лубяной слой, сосудистый слой. Лубяной слой крапивы содержит элементарные волокна овальной формы неодинаковой толщины с поперечным размером 10-30 мкм. Для выделения лубяных волокон провели химическую варку снятых с зеленого стебля оболочек крапивы в 2 %-ном водном растворе кальцинированной соды в течение 18 часов. Упруго-прочностные характеристики выделенных технических волокон толщиной 60-290 мкм определяли при растяжении на приборе ТМА-60. Найденные значения прочности и модуля Юнга увеличиваются с уменьшением поперечного сечения технических волокон и достигают 306,7 МПа и 12,67 ГПа, соответственно, при толщине образца 60 мкм. Полученные результаты экспериментальных исследований согласуются с известными литературными данными по свойствам волокон лубяных растений – лен, конопля, крапива двудомная и рами, которые уже находят применение в композиционных материалах. Благодаря достаточной длине выделенных лубяных технических волокон крапивы, на их основе могут быть изготовлены ориентированные полимерные композиционные материалы, например методом мокрой намотки. Modern world trends in the development of polymer composite materials are aimed at reducing the negative impact on the environment during the manufacture, operation and disposal of such materials. In this regard, biocomposites reinforced with plant fibers are the most promising. Due to the environmental friendliness of plant fibers, their low weight, combined with high mechanical properties and biodegradability, composites based on them are already being used in the automotive industry, construction and other industries. Herein, we examined urtica dioica samples harvested in the Republic of Altai, August 2022. This study aimed to isolate industrial urtica dioica fibers and test them lengthwise and crosswise, and measure the geometry and physical mechanics of the isolated fibers. The structures of the cross-sectional urtica dioica stem and of the isolated bast fibers were examined by scanning electron microscopy. The SEM images of the stem clearly showed the three regions: the outer layer, bast layer, and vascular layer. The bast layer of urtica dioica contains unequally-thick, oval-shaped elementary fibers of 10-30 μm in cross-section. The fibers were isolated by chemical digesting the green stem shell ripped of urtica dioica in a 2% calcined soda for 18 h. The elastic-strength characteristics of the isolated industrial fibers of 60–290 μm thick were tested to tension on a TMA-60 device. The resultant strength and the elastic modulus were increasing with a decrease in the cross-section of the industrial fibers, achieving 306.7 MPa and 12.67 GPa, respectively, with the sample thickness being 60 μm. The obtained results of experimental studies are consistent with the known literature data on the properties of fibers of bast plants - flax, hemp, stinging nettle and ramie, which are already being used in composite materials. Due to the sufficient length of the isolated bast technical fibers of nettle, oriented polymer composite materials can be made on their basis, for example, by wet winding.

Рассмотрена лубяная техническая культура конопля, сегмент по выращиванию и переработке которой в России развивается быстрыми темпами. На примере мировых тенденций показаны возможности и перспективы использования лубяных волокон конопли для биоразлагаемых композитов на растительной основе. Исследованы режимы выделения лубяных волокон методом химического реттинга. С помощью химического анализа определено содержание целлюлозы, лигнина, пентозанов в выделенных волокнах исходном растительном сырье. Методом ТМА измерены значения прочности 177-548 МПа, деформации при разрушении 0,7-2,5 % и модуля Юнга 13,2-43,5 ГПа, при толщине технических волокон от 50 до 140 мкм. Полученные результаты согласуются с известными данными других авторов и находятся на уровне свойств лубяных волокон культур – крапивы, льна, применяемых в композиционных материалах. Выделенные технические волокна конопли имеют достаточно высокие упруго-прочностные характеристики, а их длина 200-400 мм позволяет создавать армированные композитные материалы на их основе. The bast technical crop hemp is considered, the segment for the cultivation and processing of which is developing rapidly in Russia. On the example of global trends, the possibilities and prospects of using hemp bast fibers for biodegradable plant-based composites are shown. The modes of isolation of bast fibers by chemical retting were investigated. Chemical analysis was used to determine the content of cellulose, lignin, and pentosans in the isolated fibers of the original plant material. The TMA method measured strength values of 177-548 MPa, deformation at fracture of 0.7-2.5% and Young's modulus of 13.2-43.5 GPa, with a thickness of technical fibers from 50 to 140 microns. The results obtained agree with the known data of other authors and are at the level of properties of bast fibers of crops - corn, flax, used in composite materials. The selected technical hemp fibers have sufficiently high elastic-strength characteristics, and their length of 200-400 mm makes it possible to create reinforced composite materials based on them.

Using the Pareto method, the EDI binder formulation has been optimized in terms of binder rheological, strength, and heat-resistance properties. Compositions with a content of Iso-MTHFA hardener ranging from 85 to 90 wt pts and a content of UP 606/2 polymerization accelerator ranging from 0.9 to 1.1 wt pts per 100 wt pts of ED-20 resin are proposed for the manufacture of composites based on basalt and glass fibers by means of wet winding and pultrusion having the best set of these properties.

Three batches of unidirectional basalt fiber reinforced polymer were fabricated in the form of plates. Long tests were conducted over 365 days in a loaded state at room temperature, as well as in a closed desiccator at 99% humidity. The moisture absorption of unloaded samples in the desiccator did not exceed 0.20 – 0.23%. The residual mechanical properties of samples kept in a desiccator for 365 days were determined after the samples were dried: ultimate strain increased by 10 – 15%, elastic modulus by 14 – 21%, strength by 19 – 21%, and glass-transition temperature by 5 – 8°C.

Рассмотрены проблемы утилизации и вторичной переработки полимеров и композитов, одним из путей решения которой может быть создание биоразлагаемых материалов на основе растительного сырья. Проведены теоретические и экспериментальные исследования применения растительных волокон в композиционных материалах. Предложено использовать классические методы для исследований свойств растительных волокон и классические теории для расчета и конструирования структуры композитов на растительном сырье. Проведены расчеты критической длины волокон по значениям модуля упругости и прочности растительных лубяных волокон льна, крапивы и конопли, определенным экспериментально. Получены критические значения длины волокон для крапивы – 172 мкм, для конопли – 205 мкм, для льна – 273 мкм. Отмечено, что чем выше прочность и модуль упругости волокон, тем больше их критическая длина. Это может объясняться большой анизотропией свойств связующего и армирующего наполнителя. Теория монолитности предполагает равенство значений сдвиговых напряжений на границе волокно-матрица и прочности волокон. Соответственно, чем ближе свойства волокон и матрицы, тем меньшая критическая длина необходима для создания достаточной адгезии волокна к матрице. Рассмотрены примеры растительных волокон различной длины и композиты на их основе: наиболее длинных – лубяных технических волокон льна, крапивы и конопли, средних – волокон мискантуса и костры льна, и коротких – оболочек овса. The problems of utilization and recycling of polymers and composites are considered. One of the solutions may be the creation of biodegradable materials based on plant materials. Here, we theoretically and experimentally explored if plant-based fibers could be used in composite materials. We proposed that classical methods be employed to characterize plant-based fibers and that classical theories be used to predict and construct the structure of plant-based composites. The critical length of the fibers was estimated against the experimentally measured elastic modulus and strength of plant-based bast fibers of flax, nettle and hemp. The resultant critical length values were 172 µm for nettle, 205 µm for hemp and 273 µm for flax. It was noted that the higher the fiber strength and elastic modulus, the greater the fiber critical length. It can be explained by the binder and the reinforcing filler having highly anisotropic properties. The monolithicity theory implies equality between the shear stresses at the fiber–matrix interface and the fiber strength. Hence, the more similar the properties of the fibers and matrix, the shorter critical length is required to create adequate adhesion between the fiber and the matrix. Examples of plant-based fivers differing in length and composites based thereon were considered: the longest bast fibers of flax, nettle and hemp, medium-length fibers of Miscanthus and flax shover, and the shortest fibers of oat hulls.

This review provides information on the most common fibers extracted from plant lignocellulosic raw materials. Plant fibers are used as a fibrous reinforcing filler of polymer composite materials (PCMs) on various polymer matrices. The main problems in using such materials are shown—ensuring a reliable connection between the reinforcing filler and the polymer matrix, the need for protection from moisture, and instability of the mechanical properties of a fibrous reinforcing filler. The most common areas of application of PCMs reinforced with plant fibers are in the automotive industry and production of building materials. It is promising to create functional materials based on such PCM groups.

Rheological and physicomechanical properties of epoxy binders based on ED-20 epoxy resin with isoMTHPA and HT-152B (modified isoMTHPA) anhydride hardeners and of a binder based on Ethal-370 modified epoxy resin with Ethal-450 amine hardener have been studied. The pot life of the binders based on ED-20 and anhydride curing agents (isoMTHPA and HT-152B) at 25 °С is quite high. The binders based on Etal-370 and Etal-450 must be preheated before use to 40-60 °C due to the high viscosity. The highest strength of 57.3 MPa was achieved for the composite based on ED-20 and HT-152B.

Three batches of unidirectional basalt fiber-reinforced plastic were fabricated as plates, and continued tests were performed under load at room temperature and in a closed desiccator at a 99 % moisture for 365 days. The moisture absorption of the unconstrained specimens in the desiccator was not above 0.20 – 0.23 %. The residual mechanical properties of the specimens that had been held in the desiccator for 365 days were measured after being dried, and the ultimate strain was found to increase by 10 – 15 %, the elastic modulus by 14 – 21 %, the strength by 19 – 21 %, and the glass transition temperature by 5 – 8 °С.

Experimental winding of three batches of fiberglass rods was performed on a production line. The optimal composition of EDI binder was selected with component weight ratios ED-22/IMTGFA/UP-606/2 =100/85/(1.5 – 3), which raises the glass transition temperature of the products by 10 – 15°C in comparison with the control samples. The increase in the glass transition temperature was confirmed by means of TMA and DSC in all three pilot batches manufactured at different times. The heat-treatment temperatures 35 and 40°C for the new EDI composition in an impregnating bath are proposed to increase the viscosity, which provides 15% weight content of the binder in fiberglass, which meets the regulatory code specifications.

Here we explored the chemical durability of glass fiber-reinforced polymer (GFRP) bars under load. Three batches of ribbed GFRP bar specimens were fabricated using binder matrices: ED-22+isomethyltetrahydrophthalic anhydride (iso-MTGFA), ED-22+Ethal-450 and NPPN-631+ iso-MTGFA. As the reinforcing filler, we used an EC17 glass roving (for all the specimen batches). The specimens of each batch were aged in a 1 N alkaline NaOH solution at 60 °C for 2000 hrs. The ageing was performed under a 300 MPa load (30% of the failure stress). The tensile strength of the specimens from each batch following ageing was measured. The tensile test results demonstrated that that the strength loss of the specimens following chemical ageing was 58.9% for batch 1 based on ED-22+iso-MTGFA, 6.6% for batch 2 based on ED-22+Ethal-450, and 33.6% for batch 3 based on NPPN-631 + iso-MTGFA. The specimens of batch 2 based on ED-22+Ethal-450 exhibited the greatest resistance to the NaOH alkaline solution (a strength loss of 6.6%).