Wood is a combustible material. To reduce combustibility, wood is modified with functional compounds of phosphorus, boron and nitrogen, inoculation of which changes the chemical composition of the surface layer of wood and its structure. The mechanism of action of flame retardants is related to their influence on the energy and entropy characteristics of the thermodestruction process. Considering that boron nitrogen compounds are effective flame retardants and react with wood components under “mild” conditions, the effect of grafting of a borax modifier on the kinetic parameters of wood thermal decomposition is studied. The kinetic parameters (activation energy and preexponent value) are determined by thermal analysis using TGA curves (integral method). A 50 % aqueous solution of monoethanolamine (N→B) trihydroxyborate is used as a modifier; samples of unmodified pine wood are used as controls. The experimental data obtained indicate that the surface modification of pine wood with boron nitrogen fire retardant provides the material with group II fire protection efficiency (modifier consumption-150g/m2). The flame retardant effect of the boron nitrogen modifier is associated with a lower value of the activation energy of its thermal destruction process. The contribution of the entropy factor in reducing the combustibility of modified wood is less expressed. The use of monoethanolamine (N→B) trihydroxyborate as a wood flame retardant is advisable in an oxidizing atmosphere.
The difficulty of wood protection from biocorrosion and fire is due to the fact that modifiers in use are washed out from the surface of the substrate under the influence of environmental factors. This results in a rapid loss of the protective effect and other practically important wood characteristics caused by the modification. To solve this problem is the aim of our work. Here, monoethanolaminoborate is used as a modifier, where electron-donating nitrogen atom provides a coordination number equal to four to a boron atom, which determines the hydrolytic stability of the compounds formed. Alpha-cellulose ground mechanically to a particle size of 1 mm at most was used as a model compound for the modification. X-ray photoelectron spectra were recorded on the XSAM-800 spectrometer (Kratos, UK). Prolonged extraction of the modified samples preceded the registration of the photoelectron spectra to exclude the fixation of the modifier molecules unreacted with cellulose. As a result of the experiment, boron and nitrogen atoms were found in the modified substrate, which indicated the hydrolytic stability of the bonds formed between the modifier molecules and the substrate. Therefore monoethanolaminoborate can be considered as a non-extractable modifier for wood-cellulose materials.
Предмет исследования: исследование зависимости между изменением надмолекулярной структуры целлюлозы в результате модифицирования моноэтаноламин(N→B)-тригидроксиборатом и биостойкостью модифицированной древесины сосны. Цель: исследование влияния вторичной кристаллизации целлюлозы под воздействием моноэтаноламин(N→B)тригидроксиборатана на биостойкость модифицированной древесины сосны. Материалы и методы: использовали образцы воздушно-сухой целлюлозы, размер частиц 1 × 1 мм, и образцы древесины сосны размером 50 × 50 × 10 мм, последний вдоль волокон. В качестве модификатора использовали водные растворы-моноэтаноламин(N→B)-тригидроксибората МБ различной концентрации (10, 30, 50 % масс.). Образцы целлюлозы модифицировали методом погружения в растворы модификаторов. Модифицирование проводили при комнатной температуре в течение трех часов, избыток модификаторов удаляли путем экстракции дистиллированной водой. Модифицированные образцы высушивали при комнатной температуре до постоянной массы. Образцы древесины сосны модифицировали методом кистевого нанесения модификатора на поверхность. Рентгеноструктурный анализ проводили на дифрактометре марки Scientific модели ARL X'TRA Termo фирмы TermoElectron SA (Швейцария) с использованием излучения λ[CuKα]=1,5418 Å и Ni-фильтра с вращающимся образцом. Испытания образцов древесины на стойкость к воздействию плесневых и дереворазрушающих грибов проводились в лаборатории тропических технологий ИПЭЭ РАН по методике стандарта ГОСТ 9.048-89. Результаты: установлено, что модифицирование целлюлозы моноэтаноламин(N→B)-тригидроксиборатом приводит к изменению ее надмолекулярной структуры-увеличению степени кристалличности за счет вторичной кристаллизации. Увеличение степени кристалличности целлюлозы приводит к повышению биорезистентности модифицированной древесины и усиливает антисептическое действие моноэтаноламин(N→B)-тригидроксибората. Выводы: высокая эффективность моноэтаноламин(N→B)тригидроксибората в качестве антисептика обусловлена его влиянием на надмолекулярную структуру целлюлозы и токсическим действием в отношении плесневых и дереворазрушающих грибов. Оптимальная концентрация модификатора-50%-ный водный раствор, расход-150…200 г/м 2. Применение антисептиков, увеличивающих степень кристалличности целлюлозы в результате химического модифицирования,-один из возможных путей повышения биостойкости древесины при ее поверхностной обработке.
Introduction. Composite materials on the basis of epoxy resin find wide application as adhesives, coatings and structural materials whose properties it is possible to regulate by introduction of various additives including disperse fillers in the epoxy binder. Positively influencing properties of epoxy materials, the disperse fillers can reduce water resistance of the materials. This work is aimed at studying of influence of polar and nonpolar disperse fillers on structure and water absorption of the epoxy materials. Materials and methods. When obtaining composite materials, the following components were used: ED-20 epoxy resin (state standard GOST 10587-84), dibutylphthalate (state standard GOST 8728-88) plasticizer, polyethylenepolyamine (specification TU 2413-357-00203447-99) hardener, marshallite (state standard GOST 9077-82) and graphite (state standard GOST 17022-81) disperse fillers. The structure of samples was investigated by means of IR-spectroscopy method. Water absorption was determined in boiling water using the standard gravimetric method (state standard GOST 4650-2014 (ISO 62:2008)) and evaluated by sample mass variation within 120 days. Results. As a result of the conducted researches, the optimum content of the marshallite and graphite fillers in epoxy materials is established. When mass filler-to-binder ratio is equal to 15/85, water absorption of the materials is minimum. The IR-spectroscopy method showed that introduction of the marshallite polar filler in the epoxy binder promotes ordering of material structure due to formation of hydrogen bond between reactive groups of the filler and resin. Localizing in amorphous areas, particles of the graphite nonpolar filler lead to weakening of the hydrogen-bond system. Interaction of marshallite-filled samples with water is accomplished at the swelling mode, with equilibrium degree of swelling about 1 %. The mechanism of interaction of graphite-filled samples with water includes the alternating stages of dissolution and swelling, which are more expressed as compared with check samples. Conclusions. Water resistance of epoxy materials filled with disperse fillers is defined by a microstructure of the cured resin. Introduction of the marshallite polar filler in the epoxy binder leads to ordering of material structure that results in increasing of water absorption. Introduction of the graphite nonpolar filler in the epoxy binder leads to disordering of material structure that results in reducing of water absorption. Lower value of water absorption of graphite-filled epoxy material is connected with partial dissolution of the sample. Using nonpolar fillers is inexpedient for epoxy materials contacting with water.
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