Abstract:

Objective Noise pollution is harmful to people's daily life and health. Knitted materials have the characteristics of porous structure, high machinability and softness, which have research significance for sound absorption and noise reduction. According to research, polyvinyl alcohol(PVA)nanofiber membrane has excellent sound absorption performance in the low and middle-frequency band, which may be complementary to the knitted textiles. In order to verify the effectiveness of knitted fabric-based composite sound-absorbing materials in absorbing noise, we explored the sound absorption performance and other fundamental characteristics of composite material of PVA nanofiber membrane and Milano rib knit in this paper.

Method A wool/acrylic fiber (50/50) blended yarn and a 100% wool yarn were used to produce the Milano rib knitted fabrics, whose linear density is 35 tex×2 and is 42 tex ×4 respectively. PVA nanofiber membrane is prepared by the electrospinning method. By placing the knitted fabric on the receiving plate in the electrospinning device, the PVA membrane was directly formed on the knitted fabric, creating the acoustic material. Three factors that may affect the acoustic characteristics i.e., fabric density, yarn types, and use of membrane were examined by orthogonal experiment and range analysis.

Results Eight samples are tested and the test results are summarized (Fig.3). The average sound absorption coefficients of each sample at medium and low frequency (250-1 600 Hz) and high frequency (2 000-6 300 Hz) are compared. The sound absorption coefficients of the 8 samples in the middle and low-frequency band (250-1 600 Hz) are all less than 0.1, and there is no significant change. The sound absorption effect of sample No.3 is relatively better. In the high-frequency range (2 000-6 300 Hz), sample No. 1 has the best sound absorption effect, with the average sound absorption coefficient higher than 0.3, which can be used as sound absorption material for research, and the other samples have little difference in sound absorption effect. It can be seen that the factor that has the greatest impact on the sound absorption performance of the sample is the use of membrane, and the optimal combination of all factors is "density dial scale 2, wool/acrylic fiber (50/50) blended yarn and covering membrane". Multiple groups of data are obtained by multiple measurements of each fabric, and the average value is obtained (Fig.5). The samples are arranged in the order of average permeability from high to low, which is 7 > 6 > 8 > 4 > 5 > 2 > 3 > 1. The range analysis method is used for further study of the influence level of density dial scale, yarn type, and the membrane covering or not on fabric breathability, and by comparing the value of R', yarn type demonstrates the greatest influence on air permeability(Tab.6). When the level of the three factors is "density dial scale 4, wool yarn (100%), and not covering membrane", the fabric has the best air permeability. The thickness of each sample is not very different, so the influence on the sound absorption performance is not great(Fig.7 and Fig.8). The order of the weight of square meters from high to low is 5 > 3 > 2 > 1 > 8 > 6 > 7 > 4, indicating that sample No. 5 is the heaviest and sample No. 4 is the lightest. According to the areal density of the fabric, these 8 samples belong to medium thickness fabric.

Conclusion This paper explores the application of composite material combining nanofiber membrane and knitted fabric in the field of sound absorption and noise reduction. The results show that the composite material has a certain effect on sound absorption and reaches the standard of sound absorption material. This research work also investigates the optimum parameters for sound absorption of the material. The results show that the influence factors of the sound absorption performance of the composite are membrane covering or not, density dial scale, and yarn type in descending order. The optimum combination parameters are found to be density dial scale 2, wool/acrylic fiber (50/50) blended yarn, and covering membrane. The average sound absorption coefficient of the material is over 0.3 so it can be used as acoustic material. The sound absorption performance of the fabric is greatly improved by the PVA nanofiber membrane and the sound absorption coefficient of the fabric increases from the increase in the fabric density.

Key words: Milano rib knit fabric, polyvinyl alcohol, sound absorption property, electrospinning, composite