Effect Of Heat Treatment On Polyester Needle Punched Nonwovens

Needle punched nonwovens technology is an early development technology in China's nonwoven industry. The products have strong market competitiveness and occupancy rate. They are mainly used in the fields of synthetic leather, filter materials, geotextiles, decorative fabrics and so on. In recent years, due to Spunlaced With the rapid development of the technology and product performance of spunbonded and melt blown technology, people have put forward higher requirements for the performance and diversified development of Needle Punched Nonwovens Technology and products.

The research on needle punched nonwovens focuses on raw material selection, fiber quantification, needle penetration depth and density. However, there is still a lack of in-depth research on the use of heat treatment technology to improve its structure and properties. Especially for polyester needle punched nonwovens as an air filtration material, how to use heat treatment technology to improve its filtration efficiency and expand its application and environmental protection advantages need further exploration.

During heat treatment, the structure and morphologic structure of fiber will be changed, so that the structural units with lower stability will be transformed into structural units with higher stability. The microscopic changes caused by heat treatment will be comprehensively reflected in the macro properties of fibers and products, such as dimensional stability, strength, and touch.

Therefore, heat treatment process is commonly used to improve the structure and properties of nonwoven materials, so as to improve its performance and meet the application of Nonwovens in sanitary, ring filtration and geotechnical fields. To this end, we choose the appropriate temperature and time to heat the polyester needle punched nonwovens and conduct various performance tests.

The experimental material is polyester needle punched nonwovens produced by Jiangsu Ying Yang Nonwoven Machinery Co., Ltd. The equipment includes DSC-Q200 differential scanning calorimeter, R-3 stereotype dryer, YG026A fabric strength tester, LZC-H type filter material comprehensive performance test bench, CFP-1100A capillary flow pore measuring instrument, PL203 electronic balance and YG141D fabric thickness gauge.

The heat treatment part of the experiment is made of R-3 stereotyped drier. The polyester needle punched nonwovens are treated at 1 degrees, 2, 3 and 4min respectively at 210 degree C lateral fixed length. After they are removed, they are naturally cooled at room temperature and static 24h. Before and after heat treatment, the properties of the polyester needle punched nonwovens treated at different time are compared with those of the untreated ones, and the pore size is compared with that of the untreated ones. Filtration performance The diameter and pore size distribution of polyester needle punched nonwovens before and after heat treatment were tested by CFP-1100A PMI capillary flow pore measuring instrument. The efficiency of filtration of polyester needle punched nonwovens before and after heat treatment was tested by LZC-H type filter material comprehensive performance test stand.

The total velocity of polymer crystallization is controlled by the rate of crystal nucleation and the growth rate of crystal. During crystallization, temperature affects nucleation rate and crystal growth rate. When the temperature is too high, it is not conducive to the formation of nuclei. The temperature is too low, which will affect the growth rate of crystal. Crystallinity and crystal distribution have a certain effect on the physical and mechanical properties of polyester fibers and fabrics.

When the temperature rises to 180 degrees C~200 degrees C, the growth rate of the nucleus increases, while the molecular chain still has considerable movement activity, and it is easy to diffuse into the crystal lattice. The crystal growth rate also accelerates and the total crystallization rate increases rapidly. Therefore, the crystallization process needs to be very short at this temperature, basically crystallizing in 1min, and the crystal peak is sharp.

When the temperature is between 200 degrees C~230 and C, with the increase of temperature, the thermal movement of molecules is intense, and the nuclei formed by the orderly arrangement of molecular chains are unstable or not easy to form. Although the molecular motion ability is strong, the total crystallization rate is relatively low, and the time needed to complete the crystallization process increases gradually. Especially at 230 degree C, the crystallization rate is over 10min, and the crystalline peak is not obvious. So at 210 degree C, the crystallization rate is moderate.

To sum up, PET At 210 degrees C, the time of crystallization was 3min, and the heat treatment was carried out by selecting 1, 2, 3 and 4min according to the time needed to complete the crystallization. The mechanical properties of polyester needle punched nonwovens were obviously improved by heat treatment. With the increase of heat treatment time, the crystallinity was improved, the breaking strength of base cloth increased, and the elongation at break decreased.

The experimental results show that, on the one hand, with the increase of heat treatment time, the average pore size of polyester needle punched nonwovens decreases and the pore size distribution becomes narrower. On the other hand, the efficiency of particle filtration for small particle size increased, especially for particle size larger than 2.0um. The filtration efficiency increased from 46% to 70%, and the comprehensive filtration efficiency was improved.