STUDY OF POLYMER BINDERS IN THE PRODUCTION OF COMPOSITE WOOD-PLASTIC BOARD MATERIALS

ИЗУЧЕНИЕ ПОЛИМЕРНЫХ СВЯЗУЮЩИХ В ПОЛУЧЕНИЕ КОМПОЗИЦИОННЫХ ДРЕВЕСНО-ПЛАСТИКОВЫХ ПЛИТНЫХ МАТЕРИАЛОВ

Jalilov Sh.

27.04.2024 106

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17. Технология, машины и оборудование лесозаготовок, лесного хозяйства, деревопереработки и химической переработки биомассы дерева

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Jalilov Sh. STUDY OF POLYMER BINDERS IN THE PRODUCTION OF COMPOSITE WOOD-PLASTIC BOARD MATERIALS // Universum: технические науки : электрон. научн. журн. 2024. 4(121). URL: https://7universum.com/ru/tech/archive/item/17401 (дата обращения: 22.11.2024).

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ABSTRACT

The article presents the results of a study of the effect of reactive compounds on the curing process of modified reactive compounds and unmodified urea-formaldehyde resins and the identified optimal modes of their curing, in relation to the production of wood-plastic plate materials. To conduct the study, we selected the following: as a polymer binder - urea-formaldehyde resin of the KF-MT brand; quality with reactive compounds: benzene chloride, epichlorohydrin, polyvinyl chloride, gossypol resin, which is a waste product from oil and fat production, lignin, which is from alcohol production.

In this regard, there is a need to modify urea-formaldehyde resin by physical and chemical methods and improve their adhesive and physical-mechanical properties in order to produce wood-plastic boards with high strength and performance properties and durability. Based on a study of the basic physicochemical properties of unmodified and modified resins, it was established that with an increase in the content of modifiers in the resin, the content of chlorine ions increases, and the curing time decreases in the series polyvinyl chloride, epichlorohydrin, benzene chloride. It has been established that increasing the amount of modifier by more than 10% in the structure of urea-formaldehyde resin is not advisable, since this sharply increases the curing time of the resin.

АННОТАЦИЯ

В статье приводится результаты исследования влияния реакционноспособных соединений на процесс отверждения модифицированных реакционноспособными соединениями и немодифицированные мочевиноформальдегидной смолы и выявленные оптимальные режимы их отверждения, применительно к производству древесно-пластиковых плитных материалов. Для проведения исследования нами были выбраны следующие: в качество полимерного связующего - мочевиноформальдегидной смолы марки КФ-МТ; в качество реакционноспособными соединениями: хлористый бензол, эпихлоргидрин, поливинилхлорид, госсиполовая смола, являющийся отходом масложирового производства, лигнин, являющийся спиртового производства.

В связи с этим возникает необходимость модификации карбамидоформальдегидных смол физическими и химическими методами и улучшения их адгезионных и физико-механических свойств с целью получения древесно-пластиковых плит с высокими прочностными и эксплуатационными свойствами и долговечностью.

На основании изучения основных физико-химических свойств немодифицированных и модифицированных смол установлено, что с увеличением содержания модификаторов в смоле увеличивается содержание ионов хлора, а время отверждения уменьшается в ряду поливинилхлорид, эпихлоргидрин., бензолхлорид. Установлено, что увеличение количества модификатора более чем на 10 % в структуре карбамидоформальдегидной смолы нецелесообразно, так как это резко увеличивает время отверждения смолы.

Keywords: polymer, urea-formaldehyde resin, modification, reactive compounds, benzene chloride, epichlorohydrin, polyvinyl chloride, gossypol resin, lignin, composite wood-plastic plate material.

Ключевые слова: полимер, мочевиноформальдегидная смола, модификация, реакционноспособная соединения, хлористый бензол, эпихлоргидрин, поливинилхлорид, госсиполовая смола, лигнин, композиционный древесно-пластиковый плитный материал.

Introduction. Today, on a global scale, the problem of creating and implementing innovative ideas for the development of effective compositions of composite wood-plastic board materials based on high-performance polymer materials and crushed wood shavings with high physical and mechanical properties and meeting modern requirements is relevant and in demand. Therefore, the production of composite wood-plastic board materials based on highly effective polymer binders and fillers from crushed cotton stalks and their introduction into production is of particular importance for solving this problem. At the same time, the use of effective physic-chemically modified polymer binders in the production of wood-plastic board materials from crushed cotton stalks, which makes it possible to obtain their high physical, mechanical and operational properties, ensures the republic’s need for wood-plastic materials and boards, which leads to currency savings.

In this regard, increasing the physicochemical and operational properties of urea-formaldehyde resin by modifying it with reactive compounds that meet the requirements for the production of composite wood-plastic board materials based on wood fiber mass from cotton stems is an urgent problem [1-4].

Research objects and methods. To study and analyze the states of polymer binders used in the production of particle boards (chipboards) and wood-plastic materials and boards (WPPM), in this article we examined phenol-formaldehyde, urea-formaldehyde and other polymer resins [5-7].

To conduct the study, we selected the following: as a polymer binder - urea-formaldehyde resin of the KF-MT brand; quality with reactive compounds: benzene chloride, epichlorohydrin, polyvinyl chloride, gossypol resin, which is a waste product from oil and fat production, lignin, which is from alcohol production.

The results of the study and their analysis. Let us consider phenol-formaldehyde and urea-formaldehyde resins, which are widely used in the production of chipboard and WPPM [8].

Phenol-formaldehyde resin is a resin of synthetic origin and is used to make particle boards. Phenol-formaldehyde resin provides high durability and strength of adhesive joints when exposed to hot and warm water, therefore it is classified as a resin with increased water resistance [9].

Phenol-formaldehyde resin is most widely used in the manufacture and gluing of chipboards and particle boards (chipboards). This resin cures quite quickly and has fairly high adhesive strength, as well as a light color. Chipboards (chipboards), made on the basis of phenol-formaldehyde resins, are well resistant to changes in humidity and temperature fluctuations in the environment.

Phenol-formaldehyde resins in the cured state are very brittle products and therefore in most cases are used in a modified form. Unmodified resins have found application mainly in gluing wood, polystyrene foam and some other porous materials. Phenol-formaldehyde resins are obtained by polycondensation of phenol with formaldehyde. Depending on the ratio of the starting reagents and the polycondensation conditions, resins with different properties can be obtained. Thus, with an equivalent ratio of reagents or with an excess of formaldehyde in the presence of an alkaline catalyst, resole-type resins are formed; with an excess of phenol in an acidic environment, novolac resins are formed. Resol resins contain methylol groups, due to which they can enter into a further polycondensation reaction, leading to the formation of a polymer with a spatial structure - resit. The curing process, i.e. transformation into resite occurs slowly at normal temperatures - from 6 months. up to 1 year; At elevated temperatures, the curing rate increases greatly. In the presence of acid catalysts, resol resins cure at a faster rate and at room temperature.

Some characteristics of phenol-formaldehyde resins are shown in Table 1 [10].

Table 1

Characteristics of phenol-formaldehyde resins

To obtain adhesives, mainly phenol-formaldehyde resins of the resol type with a molecular weight of 700-1000 are used. Novolac phenol-formaldehyde resins are used much less frequently, mainly in modified adhesives. Resins from cresols and substituted phenols are of less interest for the production of adhesives.

Therefore, as noted above, it is necessary to modify the phenol-formaldehyde resin or replace it with another, more non-toxic resin, i.e. to urea-formaldehyde (urea).

It should be noted that in our republic, urea-formaldehyde resin is mainly used as a polymer binder in the production of wood-plastic board materials.

Urea-formaldehyde resin (M resol type fastener) is a polycondensation product of urea and formaldehyde in the presence of a catalyst.

It is colorless and can be easily painted in any color in the mass [11].

The first condensation products of urea with formaldehyde (urea resins) were obtained back in 1896, but the production of urea resins was established only in 1920-1921. [12]. Urea-formaldehyde resin is produced by the interaction of urea and formaldehyde, taken in the form of an aqueous solution - formaldehyde. The synthesis is carried out in two stages: first, dimethylolurea, which is not yet a polymer, is formed by the interaction of urea and formaldehyde in the presence of ammonia; Then, when an acid (for example, oxalic) is added, condensation occurs, leading to the formation of a polymer. The synthesis is carried out in a porcelain cup into which urea, formalin and a small amount of ammonia solution are loaded. The mixture is stirred and boiled for 8 - 10 minutes. The viscosity of the mixture gradually increases. Then oxalic acid is introduced, mixed and the mass is poured into a test tube. The test tube is placed in a thermostat and kept for 1 hour at a temperature of 50 - 60 ℃. In this case, the mass hardens: from viscous it turns into glassy.

The production of urea-formaldehyde resins for adhesives can be organized by batch or continuous methods [13].

The use of urea-formaldehyde resin was carried out with the addition of a 30% ammonium chloride solution as a hardener.

Butanolysis of urea-formaldehyde resins occurs best in a slightly acidic environment. At the same time, the process of polycondensation also continues.

The production of urea-formaldehyde resin is essentially no different from the experiment just described. Fill the test tube one third with a saturated solution of urea in formaldehyde, add 2 drops of 20% hydrochloric acid and heat the mixture over low heat to a boil. It then boils spontaneously, eventually becoming cloudy and quickly thickening, acquiring the consistency of rubber.

Urea-formaldehyde resins are also used to produce adhesives that are resistant to rot, wood pests, and light.

The use of pure urea-formaldehyde resins for impregnating paper is allowed only if the surface of the film is subsequently protected by a coating layer.

Urea-formaldehyde resins are used as binders in the production of particle boards, fiberboards, plywood and adhesives in the manufacture of furniture, carpentry, etc.

Condensation products of urea with formaldehyde are very common adhesives for gluing wood, plywood and other wood materials.

These properties have made it possible to use urea-formaldehyde resins in decorative technology, in which phenol-formaldehyde resins are unsuitable due to their dark color. Co-condensation resins of urea, thiourea and formaldehyde cure faster and have better water resistance than urea-formaldehyde resins. But they gradually become stained, which also limits their use [14].

In order to determine the effect of temperature and reaction duration on the content of halide ions and the curing time of the resin, we investigated the modification of urea-formaldehyde resin under various conditions (Table 2).

Table 2

Dependence of the curing time of compositions on the content, nature of the modifier and reaction temperature. Reaction duration - 3 hours

Reaction temperature, ℃	Modifier	Modifier content
Reaction temperature, ℃	Modifier	0	1	3	5	10	20
50	Epichlorohydrin	107	100	90	74	31	310
	Benzyl chloride	107	102	96	91	82	295
	Polyvinyl chloride	107	95	81	68	54	192
	Gossypol resin	107	100	92	78	34	302
60	Epichlorohydrin	107	93	83	70	52	306
	Benzyl chloride	107	95	91	88	77	277
	Polyvinyl chloride	107	88	77	60	47	183
	Gossypol resin	107	89	78	66	48	300
70	Epichlorohydrin	107	81	78	66	50	295
	Benzyl chloride	107	89	86	80	73	268
	Polyvinyl chloride	107	73	70	52	44	177
	Gossypol resin	107	78	74	61	42	282

Studies have shown that with increasing reaction temperature and duration, the yield of the modified resin increases and the curing time of the resins decreases. The most optimal condition for modification is temperature - 60 ℃, reaction duration - 3 hours. It was found that of the four selected modifiers, benzyl chloride has a relatively small effect on the curing of urea-formaldehyde resin. Therefore, for further use in the production of slabs, mainly polyvinyl chloride and epichlorohydrin were chosen as modifying additives [15-17].

Next, we will consider the influence of technological factors on the curing process of modified and original urea-formaldehyde resins.

It should be noted that the speed and degree of curing of the resin largely depend on the modification conditions, which include both the amount of modifier and the temperature, as well as the duration of the modification (Table 3).

Table 3

Dependence of the curing time of the KFMT binder on the content, nature of the modifier and modification temperature (modification time 3 hours)

Modification temperature T ℃	Modifier content %	Curing time, sec.
Modification temperature T ℃	Modifier content %	Epichlor-hydrin	Benzyl chloride	PVC	Gossypol resin	Lignin
Control KFMT - 107
50	5	74	91	68	97	99
	10	61	82	54	77	82
	15	180	149	112	109	112
	20	310	295	192	170	174
60	5	70	88	60	80	86
	10	52	77	47	60	62
	15	122	128	108	88	92
70	5	66	80	52	88	92
	10	50	73	44	78	82
	15	99	155	102	100	112

As can be seen from the table, a reduction in curing time is observed up to 10% modifier content. This indicates its catalytic role and increased activity of the functional groups of the polymer.

A study of the properties of gossypol resin showed that it consists of phenolic, fatty acid and unsaponifiable parts. The IR spectra of the modifier indicate the presence in it of -COOH, -OH, -C=0 and other active reactive groups that chemically interact with both the reactive groups of the resin and the components of the cotton stems.

It has been established that the improvement in the physical and mechanical properties of modified resins is associated with an increase in the completeness of their curing, as well as with a more complete realization of the chemical affinity between the urea-formaldehyde polymer and the modifier. In order to identify the picture of the curing process under pressing conditions, studies were carried out in a wide temperature range of 150-200 ℃.

The correct selection of temperature and curing time of the modified KFMT binder helps to achieve the most complete polymerization of the resin and completeness of the process, which largely determines the properties of composite boards made from cotton stems.

Next, experiments were carried out on the curing of the binder in a wide range of temperatures and times. The degree of curing of the modified resin was determined by several methods of chemical analysis: extraction in a Soxhlet apparatus, hydrolysis, and thermal analysis. A study of the dependence of weight loss after resin hydrolysis on temperature and curing time showed that with increasing curing temperature, weight loss at all times first decreases, reaching a minimum value, then rises again with the exception of samples cured at 100 ℃ (Figure 1).

In this case, the weight loss decreases depending on the curing time and tends to be stable at the time values studied. For samples cured at 180 ℃, due to the higher curing speed, weight loss decreases faster to the optimal value.

1– 100 ℃, 2– 120 ℃, 3– 140 ℃, 4– 160 ^℃, 5– 180 ℃.

Figure 1. Dependence of weight loss during hydrolysis of the modified KFMT resin on curing time at different temperatures

As can be seen from Figure 1, the duration of the curing process at 180 ℃ leads to a sharp increase in weight loss, which indicates destructive changes in the resin. The optimal value of the degree of curing for such samples is achieved at 5 minutes, but this time is not enough to form a particle board during the pressing process. Destructive phenomena in the resin can be prevented by lowering the temperature to 150-160 ℃, while the curing time increases to 7 minutes.

In order to confirm the reliability of the data on the degree of curing obtained by the extraction method, thermogravimetric studies of cured resins were carried out, making it possible to determine the degree of cross-linking in terms of resistance to thermal-oxidative destruction of resins at elevated temperatures and to determine the limiting temperature at which destruction is insignificant.

It has been established that modified resins cured at a temperature of 160-180 ℃ and a curing time of 5-7 minutes have the highest thermal stability. A further increase in temperature and time leads to an increase in weight loss during thermal decomposition, which is explained by destructive phenomena during the curing process due to the breaking of chemical bonds, which correlates with the above data.

Conclusion. Thus, we can conclude that the physicochemical properties of particle boards and wood-plastic boards using urea-formaldehyde resin are of low properties, not durable enough and do not fully meet the requirements of GOST. In this regard, there is a need to modify urea-formaldehyde resin by physical and chemical methods and improve their adhesive and physical-mechanical properties in order to produce wood-plastic boards with high strength and performance properties and durability.

The results of experimental studies showed that for urea-formaldehyde resin modified with reactive compounds, in particular, gossypol resin and epichlorohydrin in a ratio of 10:1, the best curing temperatures are 170-180 ℃ and a time of 6-7 minutes. At the same time, compared to the unmodified KFMT resin, the curing time was reduced by 2-3 minutes, which indicates a more intense polymerization of the modified resin and an increase in its heat resistance.

Based on a study of the basic physicochemical properties of unmodified and modified resins, it was established that with an increase in the content of modifiers in the resin, the content of chlorine ions increases, and the curing time decreases in the series polyvinyl chloride, epichlorohydrin, benzene chloride. It has been established that increasing the amount of modifier by more than 10% in the structure of urea-formaldehyde resin is not advisable, since this sharply increases the curing time of the resin.

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