The nonwoven fiber-reinforced TPU composites demonstrate excellent tensile properties

Thermoplastic polyurethane (TPU) is a versatile polymer that can be used to enhance the performance of fabrics such as tensile strength, flexibility and durability. It can also be used to make fabric water repellent and waterproof. It is available in a wide range of hardnesses and grades depending on the application. A variety of processing techniques can be employed in the manufacture of TPU such as extrusion, calender and blow film melt coating. The resulting TPU can be grafted onto a range of base textiles such as polyethylene, nylon and polyester. TPU composite coated fabric is a novel product which combines the advantages of a waterproof TPU membrane with the high tensile strength of a nonwoven fibre matrix composite. This can be applied to a variety of applications such as protective clothing, inflatable life vests and rafts, conveyor belts and printing blankets.

The nonwoven fiber-reinforced TPU composites demonstrate excellent tensile properties, which are in line with the intrinsic fibre mechanical properties. However, the tensile modulus can be improved by increasing the nonwoven fibre linear density and punch densities in order to increase the fibre entanglement and mechanical bonding with the TPU matrix.

In order to develop a TPU composite-coated fabric that exhibits good tensile performance with low material consumption, a hybrid process was developed. In this process, a mixture of a low molecular weight polyether TPU and a high molecular weight aromatic urethane was used to coat the nonwoven fibres. The mixture was fed into a melt coating equipment which can be either an extrusion or a calender, with the resulting TPU melt being blown as a thin film on to the base textile.

Compared to the uncoated polycotton fabric, the TPU coated one shows a more uniform surface morphology as shown in Figure 3b. The TPU layer bridges the gaps between neighboring cotton fibers resulting in a smoother surface of the bonded nonwoven. The bonded fibers are visible as convolutional ribbon profiles.

TPU composite coating also significantly enhanced the water repellency of the bonded nonwoven. The TPU possesses a low surface energy due to the siloxane groups, which results in a high water contact angle and absolute water repellency of the bonded nonwoven. This is in contrast to the PT coated fabric which demonstrates a higher water repellency due to the hydroxyl groups of the PT which bind strongly with the surface of the cellulose.

The TPU composite coated fabric also displays good oil repellency against n-heptane, n-decane and paraffin oil. However, the PT coated fabric shows poor oil repellency against n-heptane and n-decane as well as a lower surface tension than that of the TPU coated fabric.