随着工业的飞速发展，噪声污染日益严重，不仅危害人体身心健康，还会影响仪器、建筑物的寿命，是急需解决的难题之一，特别是低频噪声波长长、穿透力强，很难处理，一直是一个科技难题。噪声控制的方法中，应用吸声降噪材料是最简单、有效的手段。聚氨酯（PU）泡沫是一种已经广泛应用的多孔型吸声降噪材料，制备工艺简单、成本低廉，但其低频吸声效果普遍较差。目前，常通过添加空气层、与共振结构复合或加入多孔填料的方法改善PU的低频吸声性能，然而前两种方法会使PU材料的体积增加，不利于在一些限域空间使用，因此添加多孔填料是一种不错的选择。纤维素是一种天然生物质材料，纤维素气凝胶（CA）基于其优越的多孔结构、超高的比表面积和可生物降解性，是一种环境友好的理想吸声材料。基于此，本文探索了一种改善PU泡沫低频吸声性能的方法，将CA微球作为功能填料复合到PU多孔吸声材料中，将二者的吸声机制协同，改善传统PU吸声材料低频吸声差的问题，制备出低频吸声性能优异的纤维素气凝胶微球/聚氨酯（CA/PU）复合多孔吸声材料。取得的研究成果如下：

  （1）研究了PU原料体系中，发泡剂、催化剂、表面活性剂的添加量对PU多孔材料孔结构和吸声性能的影响。以聚醚、异氰酸酯、纯水、三乙烯二胺（DABCO）、二甲基硅油为原料，通过一步发泡法制得PU泡沫吸声材料，研究发现发泡剂、催化剂、表面活性剂的用量能影响体系发泡反应与凝胶反应的平衡，从而影响PU多孔吸声材料的密度、孔尺寸、开孔率。当发泡剂水用量为2.6 wt％、催化剂DABCO用量为0.45 wt％、表面活性剂二甲基硅油用量为3.7 wt％时，制备的PU泡沫在0-5000 Hz的综合吸声性能最好，低、中、高频平均吸声系数分别为0.17、0.70、0.94。

  （2）研究了一种简便、环保的制备微球形CA的工艺，通过控制置换溶剂的种类和浓度实现了对CA微球孔结构的调控。用NaOH/尿素体系溶解纤维素，通过乳化法制备纤维素水凝胶微球、再经叔丁醇溶剂置换和冷冻干燥工艺获得CA多孔微球材料，研究发现，叔丁醇/水溶液作为置换溶剂时，随着叔丁醇浓度的增加，溶剂结晶速率增大，晶粒尺寸下降，制得的CA微球孔径越小，孔隙率越高，密度越低，比表面积越大。50 wt%叔丁醇制备的CA微球比表面积达61.40 m²/g，平均孔径为14.04 nm，堆积密度为0.059 g/cm³，粒径集中分布在200-300 μm，平均粒径为202.0 μm，属于介孔材料。

  （3）将CA微球作为功能填料复合到聚氨酯多孔吸声材料中，研究了微球孔结构对CA/PU复合多孔材料吸声性能和力学性能的影响。通过一步共混发泡制备了CA/PU复合多孔吸声材料，研究发现，CA微球的加入使PU多孔吸声材料的吸声峰值向中、低频方向偏移，压缩强度也得到提升，比表面积越大、孔径越小的CA微球对PU泡沫低频吸声性提升越多。采用50 wt%叔丁醇制备的CA微球填充，并且填充量在1.5 wt%时，CA/PU复合多孔吸声材料在500 Hz以下低频平均吸声系数达到0.30，比单纯的PU多孔吸声材料的低频平均吸声系数提升了76.5%，填充量在2.5 wt%时，CA/PU复合多孔吸声材料的压缩强度比单纯的PU泡沫提升了3.6倍。

  With the rapid development of industry, noise pollution is becoming increasingly serious, which not only endangers human health, but also affects the life span of instruments and buildings. Noise pollution is one of the urgent problems to be solved, especially the low frequency noise has long wavelength and strong penetration, which is difficult to deal with and has always been a science puzzle. The most simple and effective way to control noise is to use sound absorbing materials. Polyurethane (PU) foam is a widely used porous sound absorption material, and its preparation process is easy and low cost, but its sound absorption in low frequency is poor. At present, air layer, resonance structure and functional filler are generally used to improve the sound absorption performance of PU in low frequency. However, the first two materials will increase the volume of PU, which is not conducive to use in some small spaces, so adding porous filler is a good choice. Cellulose is the natural biomass material. Cellulose aerogel (CA) is an ideal environmentally friendly sound absorbing material due to its porous structure, high specific surface area, and biodegradability. Based on this, this paper studies a method to improve the sound absorption performance of PU foam in low frequency , that is, adding CA microspheres into PU porous sound absorption materials as functional fillers.The combination of their sound absorption mechanism improves the sound absorption performance of PU materials in low frequency, and prepares CA/PU materials with excellent sound absorption performance in low frequency. The main research achievements are as follows:

  (1) This study examines the effects of varying amounts of blowing agents, catalysts, and surfactants within a PU raw material system on the pore structure and acoustic absorption performance of PU porous materials. Utilizing polyether, isocyanate, pure water, triethylene diamine (DABCO), and dimethyl silicone oil as raw materials, PU foam sound-absorbing materials were fabricated through a one-step foaming process. It was found that the quantities of blowing agents, catalysts, and surfactants can influence the balance between the foaming reaction and the gelation reaction, subsequently affecting the density, pore size, and open-cell content of the PU porous sound-absorbing materials. The optimal sound absorption performance across 0-5000 Hz was achieved when the formulations included 2.6 wt% water as the blowing agent, 0.45 wt% DABCO as the catalyst, and 3.7 wt% dimethyl silicone oil as the surfactant, with average sound absorption coefficients of 0.17, 0.70, and 0.94 at low, medium, and high frequencies, respectively.

  (2) The study also explored an environmentally friendly, simple method for fabricating spherical CA microspheres by controlling the type and concentration of displacement solvents to tune the pore structures of CA microspheres. Cellulose was dissolved in a NaOH/urea system, and cellulose hydrogel microspheres were prepared via an emulsification method, followed by solvent exchange with tert-butanol and freeze-drying processes. It was found that using a tert-butanol/water solution as the displacement solvent, increasing concentrations of tert-butanol accelerated the solvent crystallization rate, decreased crystal sizes, and produced CA microspheres with smaller pore sizes, higher porosity, lower density, and larger specific surface areas. Microspheres prepared with 50 wt% tert-butanol exhibited a specific surface area of 61.40 m²/g, average pore diameter of 14.04 nm, bulk density of 0.059 g/cm³, and an average particle size of 202.0 µm, predominantly in the mesoporous range.

  (3) Incorporating these CA microspheres as functional fillers into the polyurethane porous sound-absorbing material, the impact of the microspheres’ pore structures on the acoustic and mechanical properties of the CA/PU composite porous materials was studied. A one-step co-blending foaming process was used to fabricate the CA/PU composite porous sound-absorbing materials. The inclusion of CA microspheres shifted the acoustic absorption peak towards the mid and low frequency ranges and also enhanced the compressive strength. The larger the specific surface area and the smaller the pore size of the CA microspheres, the greater the improvement in low-frequency sound absorption of the PU foam. With 50 wt% tert-butanol-produced CA microspheres at a 1.5 wt% filling level, the low-frequency average sound absorption coefficient of the CA/PU composite material reached 0.30 below 500 Hz, which is a 76.5% improvement over the base PU porous sound-absorbing material. At a 2.5 wt% filling level, the compressive strength of the CA/PU composite material was 3.6 times that of the pure PU foam.

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