本文選題：酸解法　切入點：微納米級　出處：《武漢紡織大學》2017年碩士論文　論文類型：學位論文

【摘要】：水泥膠凝漿體在微結構形成過程中由于各組分水化性能差異而引起內力不均,進而產生原生缺陷是引起其損傷劣化及耐久性問題的根源。利用纖維改性水泥基復合材料成為一種有效提高其綜合性能的手段,其中纖維素纖維具有長徑比大、比強度高、比表面積大、抗拉拔韌性高、粘著吸附能力強、價格低廉等優(yōu)點,使其在膠凝漿體微結構誘導、強韌化改性方面具有突出優(yōu)勢。本文采用H_2SO_4酸解法處理脫脂棉纖維,制備得到亞微級和納米級尺度的纖維素纖維,采用紅外光譜、SEM、粒徑分析等測試手段對樣品進行表征。結果證明:纖維素纖維經酸解作用后,其特征基團、分子結構并不發(fā)生改變,而只是在尺度上逐漸減小,即天然纖維素纖維在酸解作用下逐步剝離成為直徑從十幾微米到幾百納米的纖維,其直徑隨著H_2SO_4溶液濃度的增大、反應時間的延長而逐漸減小。將不同尺度的纖維素纖維引入水泥漿體,運用SEM研究纖維素纖維尺度對膠凝漿體微結構的影響。結果表明:纖維素纖維的親水性和超強吸附性使水泥水化產物C-S-H凝膠依附在其表面生長;宏觀尺度纖維素纖維在水化早期吸水溶脹,后期釋水后發(fā)生干縮、脫空現(xiàn)象,降低水了泥漿體的密實度,從而影響水泥基復合材料的體積穩(wěn)定性;微納級纖維素纖維在尺度上與水泥水化產物C-S-H凝膠尺度匹配,其晶核作用在早期誘導水化產物沿纖維方向蔓延生長,在一定程度上促進水泥的水化,隨著纖維表面水化產物的不斷生長,纖維逐漸被包埋其中。采用IR、TG-DSC、水化熱、NMR、XRD等測試技術研究纖維素纖維對水泥水化特性的影響。結果表明:纖維素纖維初期會吸收水分降低漿體的實際水灰比,水化放熱速率低,早期放熱量低;后期水泥漿體內部水分逐步消耗,纖維素纖維所吸的水分在濕度梯度和毛細壓的作用下向外釋放,保證水泥顆粒的持續(xù)水化,故總放熱量與純水泥相當;纖維素纖維本身不參與水泥的水化反應,但微觀尺度纖維的誘導調控作用有助于提高C-S-H凝膠聚合度。本文還對纖維素纖維水泥基復合材料的宏觀力學性能進行了研究。結果表明:小尺寸纖維素纖維能夠明顯提高水泥基復合材料的抗折強度,抑制水泥漿體的收縮度,且纖維尺寸越小,效果越明顯。
[Abstract]:During the formation of the microstructure of the cement paste, the internal force is uneven due to the difference of the hydration performance of each group. Then the original defects are the root of the damage deterioration and durability problems. The use of fiber modified cement matrix composites has become an effective means to improve its comprehensive properties, among which cellulose fiber has a large aspect ratio and high specific strength. The advantages of large specific surface area, high tensile toughness, strong adhesion and low price have made it have outstanding advantages in the modification of cemented pulp microstructure and toughening. In this paper, H_2SO_4 acid hydrolysis was used to treat the degreased cotton fiber. The submicro and nanometer scale cellulose fibers were prepared and characterized by infrared spectroscopy and particle size analysis. The results showed that the cellulose fibers were characterized by acidolysis. The molecular structure did not change, but only gradually decreased on a scale, that is, natural cellulose fibers were gradually stripped off into fibers ranging from 10 microns to hundreds of nanometers in diameter under acidolysis, and their diameters increased with the concentration of H_2SO_4 solution. When the reaction time was prolonged, the cellulose fibers of different sizes were introduced into the cement paste. The effect of cellulose fiber size on the microstructure of cement paste was studied by SEM. The results showed that the hydrophilicity and super adsorption of cellulose fiber made the cement hydration product C-S-H gel grow on its surface. The macroscopical cellulose fiber absorbs water at the early stage of hydration and expands in water at the later stage of water release. The phenomenon of dry shrinkage and emptying occurs, which reduces the density of the water slurry and thus affects the volume stability of the cement matrix composite. The micro- and nanoscale cellulose fiber matches the C-S-H gel scale of cement hydration product on the scale, its crystal nucleus action induces the hydration product to propagate along the fiber direction in the early stage, and to some extent promote the hydration of cement. As the hydration products on the surface of the fibers continue to grow, The effects of cellulose fibers on the hydration properties of cement were studied by means of IR TG-DSCand NMR-XRD. The results showed that the moisture absorption of the cellulose fibers at the initial stage decreased the actual water-cement ratio of the slurry, and the hydration heat release rate was low. In the later stage of cement slurry, the moisture absorbed by cellulose fiber was released outward under the action of humidity gradient and capillary pressure to ensure the continuous hydration of cement particles, so the total heat release was equivalent to that of pure cement. Cellulose fiber itself does not participate in the hydration of cement, However, the induction and regulation of microfiber can improve the degree of C-S-H gel polymerization. The macroscopic mechanical properties of cellulose fiber cement matrix composites are also studied. The results show that the small size cellulose fiber can improve the polymerization degree of C-S-H gel. Obviously improve the flexural strength of cement matrix composites, The shrinkage of cement paste is inhibited, and the smaller the fiber size, the more obvious the effect is.
【學位授予單位】：武漢紡織大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ172.1;TB332

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