Relaxation of knitted fabrics is a
prerequisite to restoration of fabric properties and performance. The Hong Kong
Research Institute of Textiles and Apparel (HKRITA) has developed a new low
pressure relaxation (LPR) process for sweater manufacturing.
Conventional washing and tumble drying
(WTD) is used for relaxation in sweater manufacturing and is achieved by
mechanical agitation. However, it is time consuming and involves a lot of water
and energy consumption. It also adversely affects the surface texture of the
product.
Unlike the conventional WTD process, the
LPR process developed by HKRITA applies micro-agitation to achieve sweater
relaxation.
The process is based on the principle that
when air pressure drops, water evaporates and its volume expands. The force
field created by water vapour expansion in a garment acts on its fibres and
yarns, resulting in an agitation action occurring, which has a relaxation
effect on the garment. A LPR chamber is built to provide a suitable environment.
More
sustainable with less water and electricity
The LPR process is potentially beneficial
to sweater production, according to HKRITA. Compared to WTD, the new process is
far more sustainable since the LPR process uses less water and electricity with
shorter processing time, while restoring more effectively the sweater
properties of dimensional stability, fabric appearance and hand feel at the
same time.
It is estimated that the LPR process takes
only 3-5 minutes (depends on the type of fibre) to complete while WTD takes 2-3
hours. Each sweater undergoing a LPR process only consumes 0.2 litres of water
and 0.132kWh of energy.
In addition, the LPR offers a cleaner
fabric appearance, higher pilling test grade and brighter colours especially
for darker shades such as black and navy blue.