STUDY OF THE RELATIONSHIP BETWEEN THE STRUCTURE OF EPOXYSILOXANE POLYMER COMPOSITIONS AND THEIR MOST IMPORTANT PERFORMANCE PROPERTIES

ABSTRACT

This article presents the results of studies of the relationship between the structure of epoxysilane polymer compositions and their most important operational (wetting angle (0), friction coefficient (k), adhesive strength (A), holding force of adhesion (F), impact toughness (A), tensile strength (Π), relative elongation (ɛ) and microhardness (H)) properties of epoxy-dimethylsiloxane polymers. Studies have shown that as a result of aging of epoxysiloxane polymers, a decrease in their main physical, mechanical and operational properties by 15-20% is observed, for epoxy polymers - by 30-55%. The methods of mathematical planning of the experiment according to Box-Hunter were used to determine the optimal heat treatment modes and the ratio of components in the mixtures.

АННОТАЦИЯ

В данном статье приведены результаты исследований взаимосвязи между структурой эпоксисилановых полимерных композиций и их важнейщих эксплуатационных (угла смачивания (0), коэффи­циент трения (к), адгезионная прочность (А), удерживающая сила сцепле­ния (F), ударной вязкости (А), предела прочности при растяжении (П), относительного удлинения (ɛ) и микротвердость (Н)) свойств эпокси-диметилсилоксановых полимеров. Исследованиям установлено, что в результате старения эпоксилоксановых полимеров на­блюдается снижение их основных физико-механических и эксплуата­ционных свойств на 15-20%, у эпоксидных - на 30-55%. Методами ма­тематического планирования эксперимента по Боксу-Хантеру опреде­ляли оптимальные режимы термообработки и соотношения компонентов в смесях.

Keywords: wetting angle, friction coefficient, adhesive strength, adhesive holding force, impact toughness, relative elongation, microhardness.

Ключевые слова: угла смачивания, коэффи­циент трения, адгезионная прочность, удерживающая сила сцепле­ния, ударной вязкости, относительные удлинение, микротвердость.

Introduction. Recently, microisotropic materials have been used for these purposes and the performance of tooling elements based on them has not reached the required level, especially in the production of building structures with relief finishing, when the conditions for obtaining and stripping reinforced concrete structures have worsened. Therefore, the development of polymer-polymer composite materials, in particular epoxysiloxane compositions and coatings based on them with high physical, mechanical and tribotechnical properties is of particular importance and is in demand.

Objects of study: The objects of study were industrially produced and widely used in the national economy as a basis for structural materials epoxy oligomers ED-20, EC-N, UP-655. Their hardeners are piperidine, aminophenol (UP-583), monocyanethyldiethylenetriamine (UP-0633M), adduct of piperidine and epoxy oligomer ED-20 (Adduct). The siloxane oligomers are oligomethylsilsequiosane (KO-812), polyalumophenylsiloxane (KO-810), dimethylsiloxane rubber with its hardener - methyl ester of orthotitanic acid (DMSR/MEOTA). The first two siloxane oligomers are co-hardeners of epoxy oligomers. Strontium ferrite and iron powder were used as fillers to impart magnetic properties to epoxysiloxane composite materials, and GS-2 graphite was used to improve tribotechnical properties.

Research methods. The work uses the methods of DT and TG analysis, which were used to study phase transitions in epoxysiloxane polymers. The structure of epoxysiloxane polymers and composite materials was studied using optical microscopy. Identification of the composition of gradient epoxysiloxane polymers was carried out using IR spectroscopy. Surface microroughness was estimated by profiling. Determination of physical, mechanical, tribotechnical and protective properties was carried out according to standard methods and State Standard. Concrete adhesion to an element of technological equipment and the formwork stripping force were measured using the technique developed in TsNIISK. The chemical molding modes were optimized using the Box-Hunter method of mathematical planning of the experiment. The experimental data were processed by methods of mathematical statistics using the Iskra-1256 computer.

Research results and their analysis. In the first stage, the results of the studies of the microroughness of the working surface of epoxysiloxane polymer samples are discussed, as well as their tribotechnical and thermal properties depending on the composition of the mixtures and the technology of polymer production.

The heights of microroughnesses and the distance between them depend significantly on the content of the siloxane phase. It was found that small additives (1-3 parts by weight) of the siloxane component in mixtures at 293 K form high microroughnesses (20-24 μm) in epoxysiloxane polymers with a significant distance between them (0.8-1 mm). Increasing the thermostatting temperature when mixing the components to 323 K and increasing the concentration of the siloxane component to 10 parts by weight leads to a decrease in microroughnesses to 5-8 μm, and the distance between them to 0.3-0.5 mm. A further increase in the concentration of the siloxane component (up to 20 parts by weight and higher) leads to a decrease in the distance between the peaks of the surface roughness to 0.2-0.3 mm, and the siloxane phase becomes continuous [1-3].

The dependence of the tribological (friction coefficient and wear resistance) properties of epoxysiloxane polymers on the surface roughness and the ratio of oligomers in the mixture was studied. As can be seen from Fig. 1, the dependence of the friction coefficient b of the mass loss due to wear on the content of the siloxane component is extreme in nature with a clearly expressed minimum at 10 parts by weight of DMSR, which corresponds to 28% of the siloxane phase content in the working layer. Such a decrease in the coefficient of friction and wear to a minimum value is explained by the presence of both siloxane and epoxy polymers in the surface layers of the samples, which have different microhardness and tribological characteristics. The wear process of epoxysiloxane polymers apparently follows the general tribological rules of Charpy. An increase in the concentration of the siloxane component in the polymer leads to an increase in wear and friction coefficient [4-6].

From the data in Fig. 1 and Table 1 it is evident that the developed polymers have increased hydrophobicity and anti-adhesion, the temperature of onset and activation energy of destruction compared to epoxy polymers. Their values ​​pass through an extremum, which also falls on 10 mass parts of DMSR.

Figure 1. Dependence of the contact angle of wetting (0), coefficient of friction (k), loss of mass due to wear (I), adhesive strength (A), and holding force of adhesion (F) of epoxy dimethyl siloxane polymers on the content of the siloxane component

Figure 2. Dependence of impact toughness (A), tensile strength (P), relative elongation (ɛ), microhardness (H) of epoxy dimethyl siloxane polymers on the content of the siloxane component

Содержание ДМСК в рабочем слое, %

The data are given for a mixture of ED-20/PP + DMSR/MEOTA

Thus, it is clear that by regulating the content of the siloxane phase in the working layers, it is possible to significantly increase the tribological, chemical and thermal properties of polymers.

The second section of the fourth chapter presents the results of a study of the effect of the gradient distribution of the siloxane phase on their physicochemical and mechanical properties. When studying the deformation-strength dependences of polymers on the ratio of the mixture components and the molding conditions, their extreme nature was revealed. In the region of low contents of the siloxane component in such polymers, a significant increase in the static and dynamic mechanical strength indicators is observed, which is evident from Fig. 2. This is explained by the alloying effect of small additives of siloxane polymers. In this case, the siloxane components are concentrated mainly in the interstructural regions of the epoxy matrix. And these regions of epoxy polymers are the most defective. With increasing content of the siloxane component (more than 10 parts by weight), there is a monotonous decrease in the adhesive strength of polymers with steel substrates (Fig. 1) and a sharp decrease in strength indicators. Impact toughness indicators in the entire studied range monotonously increase with an increase in the siloxane component.

Conclusions. In order to predict the durability of the studied epoxysiloxane polymers in technological equipment in the production of reinforced concrete structures, their resistance to the effects of elevated temperatures (353-473 K) and alkaline environments was studied. It was found that as a result of aging of epoxysiloxane polymers, a decrease in their main physical, mechanical and operational properties by 15-20% is observed, for epoxy polymers - by 30-55%. The methods of mathematical planning of the experiment according to Box-Hunter were used to determine the optimal heat treatment modes and component ratios in the mixtures.

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