麦秸石膏复合材料力学性能和抗火性能研究

为提高麦秸利用率,增强石膏板力学性能,改善现有木基石膏板的抗火性能,试验以粒径分别为0.30～0.60和0.18～0.30 mm的粗、细2种麦秸纤维为增强相,以建筑石膏为连续相,采用复合常温固化型结构胶粘剂代替添加石膏缓凝剂的传统方式,提出了麦秸石膏复合材料初步成型和加湿增强的两步法制备工艺,并与杉木纤维和杉木刨花石膏复合材料的力学性能和抗火性能进行对比。结果表明,细麦秸纤维石膏复合材料的物理力学性能优于粗麦秸纤维石膏复合材料,其内结合强度、静曲强度、弹性模量和吸水厚度膨胀率分别为0.33 MPa、7.1 MPa、2370 MPa和2.82%,满足《LY/T1598-2011石膏刨花板》标准的要求。由于麦秸本身具有较低的导热系数和较高的灰分含量,麦秸石膏复合材料具有较杉木石膏复合材料更优的抗火性能,其点燃时间较杉木纤维石膏复合材料高,无明显热释放速率峰值。与杉木纤维石膏材料和杉木刨花石膏材料相比,细麦秸纤维石膏复合材料的总热释放量分别低48.18%和35.87%,CO2生成速率主峰分别低42.25%和38.81%,CO生成速率主峰相近,残重率略高。试件残照表明麦秸石膏复合材料试件燃烧后外观形貌更完整,炭化程度减轻。通过扫描电镜发现,麦秸纤维的外表面较光滑,石膏主要吸附在麦秸的内表面,较小纤维单元有利于增加石膏与麦秸内表面的接触面积。因此,从微观上说明了细麦秸纤维石膏复合材料的力学性能较高的原因。麦秸秆光滑的外表面几乎充满SiO2,这也说明了麦秸石膏复合材料有较好抗火性能的原因。研究可为石膏基复合材料的功能提升和麦秸石膏复合材料产品的工程应用提供参考。

Mechanical properties and fire resistance of gypsum-based composites with wheat straw

In order to improve the full utilization of wheat straw, to enhance the mechanical properties of gypsum board and to increase the fire resistance of wood-based gypsum board, a new preparation process of gypsum-based composites with wheat straw was put forward in this study. The thick and small wheat straw fiber were used as the reinforcing materials in gypsum-based composites, and their dimension were in the range of 0.30-0.60 and 0.18-0.30 mm, respectively. The gypsum was employed as the continuous phase in the composites. The ambient temperature curing structural adhesive was used to replace the traditional gypsum retarder in the new preparation process of gypsum-based composites. The preparation process consisted of an initial forming stage for initial strength and a curing stage, where the objectives were gypsum hydration and the strength further increased, respectively. Compared with the conventional gypsum composites with Chinese fir fiber and Chinese fir particle, the mechanical properties and fire resistance of gypsum-based composites by adding wheat straw fiber with different dimension were tested and analyzed. The results showed that the physical and mechanical properties of gypsum-based composites with small wheat straw fiber were lower than those of gypsum-based composites with Chinese fir fiber, but were better than gypsum-based composites with thick wheat straw fiber. The internal bond strength, modulus of rupture, modulus of elasticity and thickness swelling of gypsum-based composites with small wheat straw fiber were 0.33 MPa, 7.1 MPa, 2 370 MPa and 2.82%, respectively, and could meet the requirements of gypsum particleboard standard. According to the lower thermal conductivity and higher ash content of wheat straw than wood materials, the time to ignition of gypsum-based composites with wheat straw was higher than that of gypsum-based composites with Chinese fir fiber, and there was no obvious peak heat release rate in the fire resistance test. Compared with the gypsum-based with Chinese fir fiber and Chinese fir particle, the total heat release of gypsum-based composites with small wheat straw fiber was 48.18% and 35.87% lower, respectively. The main peak of CO2 production rate was 42.25% and 38.81% lower than that of Chinese fir fiber and particle gypsum composites, respectively. The main peak of CO production rate was comparable to wood-gypsum composites. The weight percent retains of small wheat straw fiber gypsum composites was slightly higher than that of Chinese fir gypsum composites, and the appearance after burning test was more complete and the degree of carbonization was lighter obviously. Due to the smooth outer surface of the wheat straw, the gypsum was mainly attached to the internal surface of the wheat straw by microscopic observation using scanning electron microscope. Therefore, the small straw fiber could increase the contact area between the internal surface and the gypsum, which indicated the inherent reason for the better physical and mechanical properties of small wheat straw fiber gypsum composites. The smooth outer surface of the wheat straw was almost covered with SiO2, which also explained the superior fire resistance of wheat straw gypsum composites. The study can be a reference for the performance improving on the gypsum-based composites with wheat straw fiber and its application in project.