水泥—木梗纤维复合吸声材料的组成、性能及吸声模型研究

【作者】 余海燕；

【导师】 姚燕；

【作者基本信息】 中国建筑材料科学研究总院 ， 材料学， 2006， 博士

【摘要】 针对如何制备出相容性好、吸声性能优良、结构耐久的水泥-木梗纤维复合吸声材料的关键问题，研究了木梗纤维与水泥的适应性、水泥-木梗纤维体系组成的优化以及水泥-木梗纤维复合材料的耐久性，并探讨了影响理想多孔结构的因素，建立了理想多孔吸声材料的传声与吸声模型。研究表明，组成木梗纤维的纤维素、半纤维素、木质素等是影响水泥凝结硬化的主要原因。在水化初期(1小时以内)，纤维素、半纤维素严重影响了水泥的水化硬化速度，二者的影响程度基本相当；而木质素对水泥水化硬化的影响是开始的十几分钟严重降低了水泥水化速度，17分钟到1小时内其对水泥水化的影响不是很大。在1小时到3天内，半纤维素和木质素对水泥水化硬化的抑制作用很强，而纤维素的作用相对较弱。组成木梗纤维的化学纯物质对水泥水化硬化的影响具有加和性，建立了木梗纤维与水泥相容性的预测模型，可以通过木梗纤维的化学组成初步判定其对水泥水化硬化的影响程度。加入硅灰、对木梗纤维进行热处理或氢氧化钙浸泡处理都能有效地改善木梗纤维与水泥的适应性。另外，加入促进水泥水化硬化或阻止木梗纤维分解的化学外加剂能显著改善水泥与木梗纤维的适应性。水泥-木梗纤维复合吸声材料的组成显著影响复合材料的声学性能和力学性能。实验结果表明：木梗纤维的几何尺寸对复合吸声材料的性能影响很大，由长度较长、截面较小的木梗纤维制得的复合材料具有良好的吸声性能。木梗纤维的长度对复合材料的力学性能影响很大，随着木梗纤维长度的增加，复合材料的抗折强度和断裂韧性提高。不同比例的长、短木梗纤维混掺可以制得吸声性能优异的复合吸声材料。另外，水泥-木梗纤维复合吸声材料的厚度、密度、复合材料背后设置空腔以及采用层合梯度结构等对材料的吸声性能都有较大的影响。由于木梗纤维干湿循环变形量很大，导致水泥-木梗纤维的尺寸稳定性较差。实验研究表明，经多次干湿循环后，在硬化水泥浆体与木梗纤维的界面处出现沟槽，从而降低了水泥浆体与木梗纤维之间的作用，使复合吸声材料的强度和韧性降低，并且随着干湿循环次数的增加，水泥-木梗纤维复合吸声材料的上述性能不断降低。把木梗纤维放入丙烯酸乳液、甘油酸酯和硬脂酸混合液、有机硅憎水剂中浸泡处理，能改善制品抗干湿循环的变形性能，但多次干湿循环后，复合材料的尺寸稳定性也逐渐降低。硬化水泥浆体孔溶液的碱度较高，不利于白腐菌、褐腐菌等微生物的生长，因此水泥-木梗纤维复合材料具有很高的抗生物侵蚀性。通过对多次干湿循环后试样破坏形态的研究，建立了水泥-木梗纤维复合材料的微结构和抗干湿循环破坏模型，认为水泥浆体和木梗纤维之间存在界面；在木梗纤维内部，纤维素纤维与结合相半纤维素以及木质素之间也存在界面，前者的结合主要是物理作用，后者的结合是化学作用。在非干湿循环状态下，应力破坏主要发生在木梗纤维与水泥浆体的界面处；而在干湿循环状态下，由于半纤维素与木质素在碱性环境下的水解，导致木梗纤维内部纤维素纤维与木质素以及半纤维的作用严重削弱，复合材料应力状态下的破坏主要为纤维撕裂破坏，木梗纤维内部界面成为整个复合材料的薄弱环节。通过对理想多孔体吸声性能的研究，得出孔结构是影响吸声材料的主要因素，并且在相同空隙率的条件下，随着孔径的减小吸声材料的吸声性能提高；在相同孔径的条件下，随着空隙率的增加，吸声材料的吸声性能提高。孔的长度(也就是吸声材料的厚度)也是影响材料吸声性能的因素，增加孔的长度对改变材料的吸声频率特性有很重要的影响。另外，表面层空隙率高、孔径较大而内部空隙率较低孔径较小的类层合结构有利于声波在材料内部的传播和吸收，是多孔材料理想的孔结构。同时，建立了水泥-木梗复合吸声材料声传播及吸收的模型，认为吸声材料的结构是影响材料吸声性能的关键因素，多孔材料表面的结构特点影响声波的透过性能，表面开孔率越高、孔径越大越利于声波的透过，为声波在吸声材料内部的高效吸收提供了条件；多孔材料内部结构是决定材料对声波吸收的重要条件，较高的空隙率、细化的孔结构、合理的声传播距离有利于吸声材料对声波的吸收。并且通过合理的材料结构设计可以制备出吸声性能优异的吸声材料。更多还原

【Abstract】 To develop cement-based wood fiber sound absorption material that have good compatibility between wood and cement, excellent performance of sound absorption and outstanding durability, the author has systematically studied the properties of wood and cement, optimized the composition of cement-wood fiber system, and the durability of the composite material. It is also discussed the factors that influence sound absorption of ideal porous sound absorption material. A model is established to describe sound wave absorption in ideal porous material.It is indicated that the main factors influencing the setting time of cement is the composition of wood fiber, that is, cellulose, hemicellulose and lignose. During the initial stage of hydration (less than 1 hour), cellulose and hemicellulose affect the hydration rate of cement severely, to a same extent. However, in the first ten minutes, lignose decreases the hydration rate of cement significantly. From 1 hour to 3 days, hemicellulose and lignose retarded the hydration of cement strongly. Compared with that, the effect of cellulose is much small. Based on the observations, the compatibility between wood and cement has been established. The compatibility can be improved by measures of adding silica fume into cement paste, pre-heating the wood fiber or pre-treating it using saturated lime. In addition, chemical admixtures can be used to improve the compatibility between cement and wood fiber.The composition of cement-based wood fiber sound absorption materials can influence the acoustic and mechanical performances. The result of experiment showed that, the size of wood fiber affects the performance composite greatly, and the composite made of large aspect ratio wood fiber has much better sound absorbing performance. Increasing the length of wood fiber, bending strength and toughness will be improved. The composite made of certain proportion of long and short wood fibers has excellent sound absorbing performance. In addition, thickness and density of cement-based wood fiber sound absorption materials influence the sound absorption performance. Creating cavum behind the composite or density gradient distribution will cause the first resonance frequency transfer towards lower frequency.The cement-based wood fiber sound absorption material has poor stability in dimension because wood fiber has larger distortion after several drying and wetting cycles. The result of experiment showed that, there was a groove at the interface of wood fiber and cement paste after several drying and wetting cycles. This leads to the bond reduction between wood fiber and cement paste, which results in the decrease in flexural strength and toughness. Increasing drying and wetting cycles, has the same effect with large decrease rate. Pre-treating wood fiber in 10% acrylic emulsion (by volume), or soaking in organic silicon repellent agent, the dimensional stability of composite will improve greatly. But its stability still gets worse and worse with drying and wetting cycles. Because of the rather high alkalinity of cement paste, the brown and white rot fungi cannot survive. As a result, the composite has an excellent fungi resistance. A model of micro-structure and anti cycle destruction is established through the study on destruction of cement-based wood fiber composite undergoing drying and wetting cycles. It shows that there are two interfaces in the composite, one is between cement paste and wood fiber, the other is between cellulose fiber and hemicellulose as well as lignose. The first bond is molecule force, and the second one is chemical force. Without undergoing drying and wetting cycles, the destruction occurs at the interface between cement paste and wood fiber; while after several cycles, hemicellulose and lignose will decompose under alkali environment, the bond between cellulose fiber and hemicellulose, lignose becomes very weak, therefore this interface is the weakest part in the composite.Through the study on the sound absorption property of ideal porous material, it can be concluded that pore structure is the main factor affecting sound absorption property of a composite. At the same porosity, absorption performance can be improved by reducing aperture. On the other hand, the absorbing performance can be improved with the porosity increasing at the same aperture. With the increase of pore length, the first resonance frequency transfers towards lower frequency. In addition, the distribution of higher porosity with much bigger pores at the surface and lower porosity with smaller pore inside the materials is the best pore structure for sound absorption. At the same time, a model is established to show the diffusion and absorption of sound wave. Sound absorption of material is determined by its porous structure. The higher the porosity and the bigger the aperture is, the better sound diffusion will be. On the other hand, inner porous structure of the composite is the main factor for sound absorption, the higher the porosity and the smaller the aperture is, the better sound absorption will be.更多还原