Textile Recycling Technologies, Colouring and Finishing Methods

 
 
3.1.2 Polyester Recovery and Recycling 
The grades of PET polymers differ in terms of physical properties, which ultimately affects 
recycling, and designates the intended applications. The intrinsic viscosity (IV) is an important 
physical property that is a measure of the polymer molecular weight, and is related to the material’s 
melting point, crystallinity, and tensile strength.
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PET bottle resin has a higher IV and 
crystallinity, whereas fibre grade PET for textiles and technical applications range from low to 
high IV values (Table 3).
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Application 
Intrinsic Viscosity 
Value 
Fibre Grade 
Textiles 
0.40-0.70 
Technical 
0.72-0.98 
Bottle Grade 
Water bottles 
0.70-0.78 
Carbonated soft drink grade 
0.78-0.85 
Film Grade 
Biaxially oriented PET film 
0.60-0.70 
Thermoforming sheet 
0.70-1.00 
Engineering Grade 
Monofilament 
1.00-2.00 
Table 3: Intrinsic Viscosity Values of Different PET grades. 
Reproduced from [11]. 
 
 
 

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3.1.2.1 Mechanical Recycling 
Mechanical recycling of polyester consists of a re-melt process (or melt recycling). The process 
consists of the following main steps:
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-Collection, sorting, separation, and removal of contaminants or non-target materials 
-Reduction of size – crushing, grinding, shredding, or pulling 
-Heating/re-melting, and extrusion into resin pellets 
-Melt extrusion into fibres 
-Processing of fibres to fabric 
Figure 7: General route for mechanical recycling of polyester. 
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The PET recovered from mechanical recycling is often used in lower value applications, due to 
the loss of physical properties, degradation, and contamination during use cycles and processing. 
Post-consumer PET bottles (generally higher IV value) are most often recycled into PET yarns 
(lower IV values) and is a successful example of open-loop recycling. From 2015, the market of 
recycled PET spun into yarns from plastic bottles, apparel materials increased by 58%.
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The 
reverse process is not commonly practiced, due to low prices and high production capacity for 
virgin PET resin, thereby resulting in a very low incentive to invest in technology to upgrade lower 
IV materials to meet higher value specifications. Polyester from post-industrial waste or post-
consumer PET bottles most often undergo fibre-to-fibre mechanical recycling, and ease in 
recycling by this route is due to the waste material properties being relatively close to 100% PET.
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However, maintaining quality of respun polyester is a challenge in mechanical recycling, along 
with decolourization and loss of mechanical properties, as cheaper recycled polyester materials are 
known to have yellowing problems when respun from mechanical recycling routes.
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Varied 
material composition or contamination from post-consumer textile waste would be more difficult 
to mechanically recycle back into polyester fibre.
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Other options for the mechanical recycling of pre-consumer and post-consumer PET textile waste 
generally include end uses for filler materials or nonwoven materials, for furniture, mattresses, 
insulation, or automotive lining.
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