Preparation and properties of polyvinyl alcohol-carbon black/hollow sphere foam sound absorption composites
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摘要: 噪声污染影响人类心理和生理健康。多孔材料在中高频段吸声性能较好，但在低频段较差。本文以粉煤灰空心球和水玻璃等为原料，采用两次固化成型工艺制备了空心球泡沫多孔基体材料，再通过真空浸渍、普通热干燥或冷冻干燥等方法在多孔材料中引入柔性聚乙烯醇-炭黑(PVA-C)第二相，最终制得了PVA-C/空心球泡沫复合吸声材料。结果表明：所制备的多孔复合吸声材料的抗压强度达到1.65 MPa，吸声性能相比空心球泡沫多孔材料基体在低频100~1000 Hz提高了35.2%，降噪系数达到0.523，提高了10.1%。研究结果为多孔吸声材料的吸声性能改善和实际应用提供了依据。Abstract: Noise pollution greatly affects human mental and physical health. Porous sound absorption materials usually perform well in middle and high frequency bands, but improvement still needs in low frequency bands. In this work, hollow sphere foam matrix were prepared with fly-ash hollow sphere and sodium silicate as the raw materials firstly. Subsequently, flexible polyvinyl alcohol-carbon black (PVA-C) composite was introduced into the porous matrix through vacuum impregnation and ordinary heat drying or freeze drying process to obtain PVA-C/hollow sphere foam composites. The results show that the compressive strength of the obtained porous composite is more than 1.65 MPa. The sound absorption performance is improved by 35.2% in the range of 100-1000 Hz, compared with the hollow sphere foam matrix. The noise reduction coefficient reaches 0.523, which is increased by 10.1%. The results of the study provide a basis for the improvement of sound absorption performance and practical application of porous sound absorbing materials.
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噪声影响人类的工作生活和心理健康，甚至会对听力系统造成不可逆转的伤害[1-2]。多孔吸声材料，如聚合物泡沫[3]、多孔纤维[4]、多孔陶瓷[5]及金属泡沫[6]等，内部具有无数细微孔隙，孔隙之间彼此连通，因此在中高频段(>1000 Hz)拥有优异的吸声性能[7-12]，但是在低频范围1000 Hz以下吸声效果不佳[13-17]。
通过将薄膜材料与多孔材料有机结合，可在低中高全频段实现吸声。例如，Nine等[18]在网格型三聚氰胺框架中自组装互连氧化石墨烯薄片，所制备的层状结构复合材料在500 Hz频率下具有72.7%的增强效果；Verdejo等[19]通过在聚氨酯中负载碳纳米管，在1~6.3 kHz中高频段的吸声性能提高了15%以上；Bechwoti等[20]研究了低频声波在活性炭中的传播，得出活性炭对低频声波的过量吸收主要是由于表面声抗的降低而不是表面声阻的变化引起的。碳材料和薄膜材料的引入，不仅可以提高黏滞作用及热效应，还可以提高材料的阻尼效应，在气固界面处将更多的声能转化为热能，进而提高吸声性能。
炭黑具有较大的比表面积和优异的物理性能，是多孔材料常用的填充材料[19, 21]，同时聚乙烯醇(PVA)具有优异的抗拉强度和柔性，成膜性好[22]。基于此，本文设计了一种新颖的聚乙烯醇-炭黑(PVA-C)/空心球泡沫复合吸声材料。首先通过超声和磁力搅拌得到均匀的PVA-C悬浮液，而后采用真空浸渍、普通热干燥或冷冻干燥等方法在空心球泡沫多孔材料涂覆PVA-C，优化多孔材料内部孔结构，以改善材料的低频吸声性能。
1. 实验材料及方法
1.1 原材料
粉煤灰空心球(郑州浩达，一级粉煤灰，粒径600~800 μm)、水玻璃(德望化工，模数2.0~3.5)、碳酸钠(阿拉丁，99.5%)、四硼酸钠(阿拉丁，99.5%)、氢氧化钠(阿拉丁，98%)、聚丙烯短纤维(汇祥纤维，长度2~3 mm)及炭黑(金利化工，纳米级)、聚乙烯醇1788型(阿拉丁，分析纯)、分散剂BYK180(德国毕克，分析纯)、聚乙烯吡咯烷酮K30(上海沃凯，分析纯)。
1.2 聚乙烯醇-炭黑(PVA-C)/空心球泡沫复合吸声材料的制备
空心球泡沫多孔基体材料制备：称取100 g水玻璃和7.5 g片状NaOH，磁力搅拌使NaOH完全溶解，得到溶液1；另将5 g Na2B4O7、2 g Na2CO3和33.3 g去离子水混合，在80℃水浴锅中加热搅拌直至粉末完全溶解，得到溶液2；然后将溶液2倒入溶液1中搅拌至澄清，得到待用的水玻璃溶液A；然后取75 g粉煤灰空心球与0.5 g聚丙烯纤维混合均匀得到混合干料B，将混合干料B与水玻璃溶液A倒入不锈钢圆柱形模具中，在烘箱中100℃固化24 h而后提高至120℃固化12 h两次成型，脱模即得空心球泡沫多孔基体材料，记为HSFS。
PVA-C/空心球泡沫多孔复合材料的制备：先将不同含量的炭黑在100 mL去离子水中超声分散30 min，随后加入0.5 g分散剂BYK180和0.1 g PVP，磁力搅拌12 h至分散均匀，然后加入3 g的PVA在80℃水浴锅中加热搅拌至完全溶解，取出后室温继续搅拌6 h，最终得到均质PVA-C悬浮液。将均质PVA-C悬浮液倒入装有空心球泡沫多孔基体材料的烧杯中，以空心球泡沫多孔材料为基体，真空浸渍PVA-C悬浮液30 min。最后，将浸渍有PVA-C悬浮液的空心球泡沫多孔材料干燥处理，得到PVA-C/空心球泡沫复合吸声材料。将80℃普通热干燥6 h得到的样品记为HSFS-HD，80℃冷冻干燥48 h得到的样品记为HSFS-FD。样品命名见表1。
表 1 样品名称及制备方法Table 1. Sample name and preparation methodSample Preparation method HSFS Hollow spherical foam porous materials HSFS-HD HSFS impregnated with polyvinyl alcohol-carbon black (PVA-C) suspension is heat-dried (HD) at 80℃ for 6 h HSFS-FD HSFS impregnated with PVA-C suspension is freeze-dried (FD) at 80℃ for 48 h PVA-C composite film PVA-C suspension dried on glass substrate at 80℃ for 4 h 同时，为了考察PVA-C悬浮液的成膜性能，将聚乙烯醇∶炭黑(PVA∶C)不同质量比的悬浮液在玻璃基板上涂膜，80℃干燥4 h，得到PVA-C复合薄膜。
1.3 表征方法
用梅特勒热重仪(TG 3+，梅特勒-托利多公司)测试样品的失重，99.99% 的氮气作为保护气体，测试温度范围30~700℃，升温速率为10℃/min。用X射线衍射仪(3 kw-D/MAX2500 V，Rigaku)分析其物相，Cu Kα，波长λ=0.15406 nm，扫描步长10°/min。用傅里叶红外光谱仪(FTIR，Bruker VERTEX 70型)测试样品表面基团，KBr压片法，扫描范围400~4000 cm−1。用光学显微镜(TSView，上海光学仪器厂)和扫描电子显微镜(Flex SEM 1000，日立高新公司)观察和分析样品的表面形貌。样品的孔隙率采用阿基米德排水法测定。采用阻抗管仪器吸声测试系统(北京声望声电技术有限公司，SW477/SW422型)测试样品的吸声性能，传递函数法计算样品的吸声系数α，根据下式计算250、500、1000和2000 Hz下吸声系数的平均值记为降噪系数(NRC)：
NRC=α250Hz+α500Hz+α100Hz+α2000Hz4 (1) 2. 结果与讨论
2.1 PVA-C的形貌分析
PVA-C的光学显微镜照片(图1(a)~1(d))和分散液实物照片(图1(e))显示存放数天后，制备得到的PVA-C均质悬浮液依旧稳定，没有出现分层、沉降现象。这是由于PVA吸附在炭黑表面，作为稳定剂阻止了炭黑颗粒的团聚和沉降。悬浮液干燥后得到的薄膜照片(图1(e))显示PVA-C复合薄膜具有一定的柔韧性和强度。
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图 1 PVA∶C不同比例分散液的光学显微镜照片：(a) 5∶1；(b) 10∶1；(c) 20∶1；(d) 50∶1；(e) PVA-C复合薄膜与PVA-C悬浮液照片Figure 1. Optical microscope photographs of dispersions with different PVA∶C ratios: (a) 5∶1; (b) 10∶1; (c) 20∶1; (d) 50∶1; (e) Photographs of PVA-C film and dispersions图2展示了多孔材料HSFS基体及PVA-C/空心球泡沫复合吸声材料HSFS-HD和HSFS-FD的SEM图像。如图2(a)、2(b)所示，多孔材料基体是由空心球颗粒黏结构成相互连通的骨架结构及骨架之间的孔隙构成，孔隙在亚微米尺度。孔隙之间的相互连通有利于入射声波的进入及声波在孔隙内部的传播损耗。真空浸渍后两种不同的干燥方法可以实现PVA-C与空心球泡沫多孔材料的有效结合(图2(c)~2(f))。普通热干燥后的复合吸声材料HSFS-HD空心球外壁紧密地包覆了一层PVA-C复合薄膜，孔隙的连通性和孔隙率得以很好地保持(图2(c)、2(d))。图2(e)、2(f)显示冷冻干燥后在复合吸声材料HSFS-FD空心球外壁形成了PVA-C复合三维多孔网状结构，该结构增加了孔形状的复杂度，也有利于增强声波损耗。
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图 2 多孔材料基体((a), (b))、普通热干燥((c), (d))和冷冻干燥((e), (f))处理后附着在基体内孔壁的PVA-C (10∶1)复合薄膜的SEM图像Figure 2. SEM images of porous matrix ((a), (b)), PVA-C (10∶1) composite film adhered to the innerwall of the matrix pore after heat treatment ((c), (d)) and freeze drying ((e), (f))2.2 PVA-C的结构与物相组成
为了研究PVA-C的物相和表面基团组成，同时排除粉煤灰等组分的干扰，单独对PVA-C薄膜做了XRD和FTIR测试。图3为不同 PVA-C 复合薄膜的 XRD 图谱，可以看出，炭黑在24.08°处和44.36°处出现了C(111)和(100)的衍射峰。纯PVA的主衍射峰出现在19.38°，对应的晶面为(101)晶面 。随着共混物中PVA含量的增加，C在44.36°的衍射峰消失。同时衍射峰逐渐发生左移，PVA-C不同比例(5∶1、10∶1、20∶1、50∶1)的样品对应的衍射峰分别出现在22.92°、20.10°、20.06°和19.9°。这表明随着PVA的加入，PVA-C复合膜的结晶度降低。
图4为不同PVA-C复合薄膜的FTIR 图谱，3626 cm−1和3440 cm−1处的吸收峰是PVA分子、炭黑表面及KBr吸水造成的O—H拉伸峰，1580 cm−1左右的吸收峰是炭黑表面类醌结构C=O伸缩的特征吸收峰[23]。2940 cm−1处对应PVA分子中C—H非对称拉伸峰，1445 cm−1处对应C—H2的弯曲振动峰，1041 cm−1处对应C—O—C拉伸峰[24-25]。这一结果进一步证实PVA和C已成功复合在一起。
2.3 PVA-C的热稳定性
热稳定性是建筑材料应用中必须考虑的一个重要因素。图5为PVA-C复合薄膜的热重分析曲线及局部放大图。炭黑在600℃发生快速氧化，650℃失重平衡，而PVA在500℃左右失重接近平衡，其失重主要是由于羟基的脱水及碳链的分解。炭黑与PVA相比，热稳定性更高。因此PVA-C复合薄膜相比纯的PVA具有更高的热稳定性。并且PVA-C复合薄膜的失重率远小于纯炭黑和纯PVA。随着PVA-C质量比的降低，失重率进一步降低。
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图 5 不同PVA-C复合薄膜的TG分析曲线(a)及其局部放大图(b)Figure 5. TG analysis curves (a) of different PVA-C composite films and partial enlarged figure (b)2.4 PVA-C的吸声性能
图6为采用热干燥制备的不同PVA∶C比例(5∶1、10∶1、20∶1和50∶1)多孔复合材料(厚度均为30 mm)的吸声系数曲线。这些材料在低频和高频都有良好的吸声性能，其中低频(<1000 Hz)吸声性能相比于未加PVA-C，分别提高了16.1%、12.2%、7.6%和7.6%。当PVA∶C比例为5∶1、10∶1、20∶1时，多孔复合材料在1000~6300 Hz高频范围的平均吸声系数分别为0.687、0.729和0.672，对比未加PVA-C分别提高了2.8%、9.1%和0.6%，而PVA∶C比例为50∶1时的平均吸声系数则下降了2.2%。这是由于C含量具有相对优值，C含量过低时高频声波在PVA-C界面处的吸收较弱，存在更多的反射，从而导致吸声系数下降。4种复合材料对应的降噪系数(NRC)分别为0.519、0.521、0.486和0.485，当PVA∶C比例为10∶1时，此时的降噪系数最大。
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图 6 不同PVA∶C比例下空心球泡沫多孔复合材料的吸声系数曲线(热干燥) (a)和曲线的局部放大图 (b)Figure 6. Sound absorption coefficients of porous composites with different PVA∶C ratios obtianed by heating drying (a) and its partial enlarged figure (b)![]()
图 7 多孔材料基体与两种干燥方法处理后所得PVA-C/空心球泡沫多孔复合材料的吸声系数曲线(a)和曲线的局部放大图 (b)Figure 7. Sound absorption coefficients of porous marix and PVA-C/hollow sphere foam composites obtained by two different drying methods (a) and its partial enlarged figure (b)当PVA∶C比例为10∶1时，比较冷冻干燥处理得到的泡沫多孔复合材料(HSFS-FD)与多孔材料基体(HSFS)和热干燥(HSFS-HD)得到的泡沫多孔复合材料的平均吸声系数和降噪系数。图7为HSFS、HSFS-HD和HSFS-FD多孔复合材料(厚度30 mm)的吸声系数曲线。可以看出无论是普通热干燥还是冷冻干燥处理，引入PVA-C后，100~1000 Hz低频的吸声性能均有明显提高(12.2%和35.2%)。这是由于低频入射声波引起柔性PVA-C复合薄膜的振动，消耗了低频噪声，与文献中的结论一致[26]。在高频1000~6300 Hz，热干燥和冷冻干燥样品表现出不同的吸声效果，热干燥得到的样品提高了9.1%，而后者冷冻干燥得到的样品下降了2.4%。这两种样品的降噪系数NRC分别提高了9.7%和10.1%。表2为不同PVA∶C比例下多孔复合材料的平均吸声系数和降噪系数对比。
表 2 不同PVA∶C比例的多孔复合材料平均吸声系数α和降噪系数NRC的比较Table 2. Comparison of average sound absorption coefficient α and NRC of porous composites with different PVA∶C ratiosSample α100-1000 Hz α1000-6300 Hz NRC HSFS 0.304 0.668 0.475 HSFS-HD (5∶1) 0.353 0.687 0.519 HSFS-HD (10∶1) 0.341 0.729 0.521 HSFS-HD (20∶1) 0.327 0.672 0.486 HSFS-HD (50∶1) 0.327 0.653 0.485 HSFS-FD 0.411 0.652 0.523 Notes: α100-1000 Hz—Average sound absorption coefficient in the 100-1000 Hz frequency;
α1000-6300 Hz—Average sound absorption coefficient in the 1000-6300 Hz frequency; NRC—Noise reduction coefficient of the sample.相比热干燥，冷冻干燥处理后在孔隙内部形成了PVA-C复合三维网状薄膜，这一结构增加了空气的流程和流阻，使原本大孔结构变成了由多小孔组成的网状结构，意味着孔径减小。PVA-C复合三维网状薄膜附着在多孔材料孔隙内部时，其材料声阻抗的实部增加，增加的阻力大约是由膜的气流阻力乘以膜的厚度所决定，正如文献[27]中所报道。同时，由于高频声波在PVA-C复合网状薄膜在界面处穿透能力较弱，部分被反射，吸收减少，因此在高频段吸声性能略有下降[28]。质量密度定理决定，与中高频声波相比，穿透能力强的低频声波更难以被反射和吸收[28]。
STL=10lg[1+(πfρdρ0ccosθ)2] (2) 式中： STL表示声波的传播损失；f为声波的频率；ρ0为空气的质量密度；c为声波在空气中的速度；θ为入射声波的入射角度；d为材料的厚度；ρ为材料的质量密度。因此，当PVA-C复合薄膜引入多孔材料时，多孔材料对低频声波的入射和传播没有明显影响。此外，当声波在狭窄地孔隙中传播时，热损失和黏滞作用会导致声能的损耗。在100~1000 Hz低频范围，由于普通热干燥后PVA-C复合薄膜附着在空心球外壁，不像冷冻干燥后可以形成三维网状结构，因此PVA-C复合薄膜的振动效应不如PVA-C三维网状结构[29-30]。总之，引入PVA-C复合薄膜可以产生黏弹性薄膜固有的阻尼特性，除了增加摩擦和复合薄膜界面之间的声波耗散之外，薄膜的振动也进一步损耗声波能量，从而提高了材料的吸声性能。
声波在多孔复合材料中的传播如图8所示。声波通过空心球泡沫多孔材料传播时，一部分声能在孔隙中多次反射，与孔壁形成摩擦，产生黏滞作用与热效应而被吸收；另一部分声能被空心球内部空气柱的振动所耗散，如图8(a)所示。当空心球泡沫多孔材料外壁涂覆PVA-C时(图8(b))，在界面处产生大量的声反射和气流摩擦，导致入射声波耗散。如图8(c)所示，网状结构将多孔材料内部孔隙重新划分，使入射声波的传播路径更加曲折，声程增加，类似于增加多孔材料的厚度[31]。此外，当声波穿过PVA-C复合材料时，声能通过炭黑颗粒的吸收、反射和折射及炭黑与PVA之间的摩擦而被有效地耗散[32-33]。
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图 8 3种多孔吸声材料声波传播示意图Figure 8. Schematic diagram of sound wave propagation of three porous sound absorbing materials多孔吸声材料除孔结构外，厚度也是影响吸声材料性能的主要因素，尤其对低频吸声性能而言。因此，本文制备的吸声材料与文献中报道的不同厚度的材料进行了对比，从图9可见，本工作报道的多孔复合材料的NRC值优于大部分吸声材料[28, 34-55]，且在500 Hz下具有良好的吸声系数，扩宽了多孔吸声材料的频率范围。
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图10为3种材料的应力-应变曲线，抗压强度达到1.65 MPa以上。对比HSFS，复合后其弹性模量出现降低，这是由于HSFS在水中浸渍后软化导致的，两种干燥方式不同，冷冻干燥时间相比与热干燥，干燥时间更长，因此其弹性模量下降程度也更大。对比其他文献中多孔吸声材料的抗压强度(表3)，除了钢渣[14]和地聚物[52]，本文所制备的多孔复合材料的抗压强度是最高的。
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图 10 三种不同多孔吸声材料的应力-应变曲线Figure 10. Stress-strain curves of three different porous sound absorbing materials表 3 近年来文献报道的多孔吸声材料抗压强度比较Table 3. Comparison of the compressive strength of porous sound-absorbing materials reported in recent works3. 结 论
本文报道了一种聚乙烯醇-炭黑 (PVA-C)增强多孔吸声复合材料。主要考察了PVA-C/空心球泡沫复合材料所采用的干燥方式及聚乙烯醇∶炭黑(PVA∶C)不同比例对复合材料微观形貌、吸声性能及力学性能的影响，同时阐述了复合材料吸声强化机制。具体结论如下：
(1) 对于采用热干燥和冷冻干燥获得的样品，添加PVA-C的多孔复合材料在100~1000 Hz范围内的平均吸声系数分别提高了12.2%和35.2%，降噪系数NRC分别提高了9.7%和10.1%；
(2) 同时PVA-C增强多孔吸声复合材料具有良好的力学性能，抗压强度达到1.65 MPa。复合后，其抗压强度无明显变化，弹性模量略有下降；
(3) 在刚性吸声体中引入柔性第二相材料，不仅增加摩擦和复合薄膜界面之间的声波耗散，而且薄膜振动也进一步损耗声能，有利于强化低频吸收，进而提高多孔材料的低频波段吸声性能。
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图 1 PVA∶C不同比例分散液的光学显微镜照片：(a) 5∶1；(b) 10∶1；(c) 20∶1；(d) 50∶1；(e) PVA-C复合薄膜与PVA-C悬浮液照片
Figure 1. Optical microscope photographs of dispersions with different PVA∶C ratios: (a) 5∶1; (b) 10∶1; (c) 20∶1; (d) 50∶1; (e) Photographs of PVA-C film and dispersions
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图 2 多孔材料基体((a), (b))、普通热干燥((c), (d))和冷冻干燥((e), (f))处理后附着在基体内孔壁的PVA-C (10∶1)复合薄膜的SEM图像
Figure 2. SEM images of porous matrix ((a), (b)), PVA-C (10∶1) composite film adhered to the innerwall of the matrix pore after heat treatment ((c), (d)) and freeze drying ((e), (f))
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图 5 不同PVA-C复合薄膜的TG分析曲线(a)及其局部放大图(b)
Figure 5. TG analysis curves (a) of different PVA-C composite films and partial enlarged figure (b)
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图 6 不同PVA∶C比例下空心球泡沫多孔复合材料的吸声系数曲线(热干燥) (a)和曲线的局部放大图 (b)
Figure 6. Sound absorption coefficients of porous composites with different PVA∶C ratios obtianed by heating drying (a) and its partial enlarged figure (b)
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图 7 多孔材料基体与两种干燥方法处理后所得PVA-C/空心球泡沫多孔复合材料的吸声系数曲线(a)和曲线的局部放大图 (b)
Figure 7. Sound absorption coefficients of porous marix and PVA-C/hollow sphere foam composites obtained by two different drying methods (a) and its partial enlarged figure (b)
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图 8 3种多孔吸声材料声波传播示意图
Figure 8. Schematic diagram of sound wave propagation of three porous sound absorbing materials
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图 9 近年来文献报道的多孔吸声材料吸声性能比较：(a) 不同试样厚度与500 Hz处吸声系数对应关系；(b) 不同试样厚度与降噪系数对应关系[28, 34-55]
Figure 9. Comparison of the sound absorption properties of porous materials reported in recent work: (a) Sound absorption coefficient of samples with different thicknesses at 500 Hz; (b) Noise reduction coefficient of samples withdifferent thicknesses[28, 34-55]
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图 10 三种不同多孔吸声材料的应力-应变曲线
Figure 10. Stress-strain curves of three different porous sound absorbing materials
表 1 样品名称及制备方法
Table 1 Sample name and preparation method
Sample Preparation method HSFS Hollow spherical foam porous materials HSFS-HD HSFS impregnated with polyvinyl alcohol-carbon black (PVA-C) suspension is heat-dried (HD) at 80℃ for 6 h HSFS-FD HSFS impregnated with PVA-C suspension is freeze-dried (FD) at 80℃ for 48 h PVA-C composite film PVA-C suspension dried on glass substrate at 80℃ for 4 h 
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表 2 不同PVA∶C比例的多孔复合材料平均吸声系数α和降噪系数NRC的比较
Table 2 Comparison of average sound absorption coefficient α and NRC of porous composites with different PVA∶C ratios
Sample α100-1000 Hz α1000-6300 Hz NRC HSFS 0.304 0.668 0.475 HSFS-HD (5∶1) 0.353 0.687 0.519 HSFS-HD (10∶1) 0.341 0.729 0.521 HSFS-HD (20∶1) 0.327 0.672 0.486 HSFS-HD (50∶1) 0.327 0.653 0.485 HSFS-FD 0.411 0.652 0.523 Notes: α100-1000 Hz—Average sound absorption coefficient in the 100-1000 Hz frequency;
α1000-6300 Hz—Average sound absorption coefficient in the 1000-6300 Hz frequency; NRC—Noise reduction coefficient of the sample.
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表 3 近年来文献报道的多孔吸声材料抗压强度比较
Table 3 Comparison of the compressive strength of porous sound-absorbing materials reported in recent works
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目的
噪声污染问题已严重影响人类心理和生理健康。因此解决噪声污染问题已成为当今社会环境保护中最重要的工作之一。吸声材料是改善环境噪声中最有效的措施。无机多孔材料不仅具有宽频带吸声特性，而且还同时满足材料的绿色环保、低成本、力学性能以及防火阻燃等条件，在吸声降噪领域具有重要的研究价值。多孔材料在中高频段吸声性能较好，但在低频段较差。
方法选用粉煤灰空心球和水玻璃为原料，通过模压-两次固化成型等工艺制备空心球泡沫材料。采用共混法制备了聚乙烯醇-炭黑( PVA-C) 悬浮液，并将空心球泡沫材料通过真空浸渍和普通热干燥或冷冻干燥等方法，在刚性吸声体中引入柔性 PVA-C 第二相材料，利用 PVA-C 复合薄膜对空心球泡沫材料基体内部孔结构进行了重新优化。
结果①FT-IR 图中可以观察到 PVA 分子和炭黑的官能团，这一结果进一步证实 PVA 和 C 已成功复合在多孔材料基体中。②SEM图显示普通热干燥后的多孔材料基体骨架内壁紧密地包覆了一层 PVA-C 复合薄膜，孔隙的连通性和孔隙率得以很好地保持；冷冻干燥后在多孔材料基体内壁形成了 PVA-C 复合三维网状结构，这种网状结构形成多孔，同时增加了孔形状的复杂度，这些都有利于增强声波损耗。③无论是普通热干燥还是冷冻干燥处理，引入 PVA-C，100-1000 Hz 低频的吸声性能均有明显提高(12.2%和 35.2%)。这两种样品的降噪系数 NRC 分别提高了 9.7%和 10.1%。④所制备的多孔复合材料的抗压强度与未复合前的空心球泡沫材料相比，复合后并未降低材料的抗压强度，抗压强度达到 1.65 Mpa 以上。
结论在刚性吸声体中引入柔性第二相材料，不仅增加摩擦和复合薄膜界面之间的声波耗散，而且薄膜振动也进一步损耗声能，有利于强化低频吸收，进而提高多孔材料的低频波段吸声性能。
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空心球泡沫多孔材料以其丰富、环保、成本低、易加工成型、吸声性能优异等优点，在吸声降噪领域吸引了越来越多的研究。但由于多孔材料对低频声波的吸收能力有限，导致其低频范围吸声性能不佳，严重阻碍了它的实际应用。
本文通过将粉煤灰空心球与水玻璃等原料在模具中经两次固化成型制备得到空心球泡沫多孔材料，再通过真空浸渍、热干燥或冷冻干燥等方法在多孔材料中引入柔性聚乙烯醇-炭黑(PVA-C)第二相，制备了一种刚性-柔性复合材料 (PVA-C/空心球泡沫)，引入PVA-C复合薄膜不仅可以产生粘弹性薄膜固有的阻尼特性，除了增加摩擦和复合薄膜界面之间的声波耗散之外，薄膜的振动也进一步损耗声波能量。结果表明所制备的多孔复合吸声材料的抗压强度达到1.65 MPa，吸声性能在低频100-1000 Hz提高了35.2%，降噪系数达到0.523，提高了10.1%。通过在刚性吸声体中引入柔性第二相材料，强化低频吸收，有效提高了多孔材料的低频波段吸声性能。
(a)不同比例PVA-C/空心球泡沫多孔复合材料的吸声性能(热干燥)，(b)多孔材料基体与两种干燥处理(HD热干燥，FD冷冻干燥)后多孔复合材料的吸声性能
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