The various types of Biodegradable? polymers/fibres and the processing conditions for their conversion into fabrics
While natural polymers are both Biodegradable? and sustainable, research is on-going to develop new synthetic polymers/fibres derived from renewable sources. For a material to fulfil the’ cradle to grave’ sustainability requirement, it must be both derived from a renewable source and be degradable (Fig. 3).
Figure 3: Degradable and sustainable polymers
Categories of Biodegradable? polymers/fibres
. Biodegradable? polymers can be classified into three main categories:
1) Natural polysaccharides and biopolymers; e.g. cellulose, alginate, wool ,silk, chitin and soya bean protein
2) Synthetic polymers, particularly aliphatic polyesters e.g. poly(lactic acid), Poly(ε-caprolactone)
3) Polyesters produced by microorganisms; e.g. poly(hydroxyalkanoate)s
Natural polysaccharides and biopolymers
Many natural polymers occur as fibres that are ready to be processed into yarns and fabrics, and which can ultimately be broken down by enzymes and metabolised in the ecosystem. Others such as Alginate, Chitin and Soya Bean Protein require processing to create useful fibres.
Cellulose Cotton processing includes dyeing, bleaching and spinning each with a negative environmental impact, so degradable and more sustainable man-made fibres maybe preferable.
Alginate is extracted from seaweed, and calcium alginate fibre is used in wound dressings and other wound management products, also for use in diagnostic swabs.
Wool Processing requires shearing, washing (generates lanolin), carding, and spinning to achieve a useful yarn. Woollen garments do decompose, but may produce methane and Nitrogen dioxide in some burial conditions, which may contribute to global warming and climate change.
Silk is documented to have been uses to suture wounds as far back as ancient Egypt and currently gaining much attention in the medical field as a bioresorbable material for tissue regeneration. (Click here)
Chitin (or chitosan) is a polysaccharide derived from crustacean (shrimps, crabs etc.). It has a structure similar to cellulose and can be combined with rayon to give a fabric with a soft feel and antibacterial properties.
More information on biopolymers can be found in the following link; ( Click here)
Degradable synthetic polymers (i.e. those created catalytically from monomers) include poly(lactic acid) (PLA) derived from a renewable ?monomer and Poly(ε-caprolactone) (PCL) from a petroleum product. A greater list of Biodegradable? polymers can be found at : (Click here)
Polymers from renewable ?aliphatic esters e.g. poly(lactic acid)
Poly(lactic acid) (PLA) is a linear aliphatic polyester derived from sugar or polysaccharide, a 100% renewable ?source, therefore sustainable and degradable. The monomer used to manufacture poly(lactic acid) is obtained from annually renewable ?crops (corn, sugarbeet, wheat, Fig. 3) in the agricultural carbon cycle which uses energy from the sun to convert carbon dioxide and water into starch or other fermentable sugar, which is fermented to lactic acid.
Figure 4: Potential feedstock for PLA production
PLA degrades by hydrolysis, and can be composted instead of being sent to landfill. Over the past few years NatureWorks LLC has developed large scale operations for the economic production of PLA polymer used for packaging and fibre applications. More information can be found in the following links
Polymers from synthetic monomers Poly(ε-caprolactone)
Poly(ε-caprolactone) (PCL) is a synthetic Biodegradable? polymer. It has mechanical properties similar to polyolefins (this is the polymer family to which polypropylene belongs), but unlike them is hydrolysable similar to polyester . However, it’s low melting point of around 60®C makes it unsuitable for many textile applications. Poly(ε-caprolactone) as a co-polymer with starch is probably best known under the trade name MaterBi produced by Novamont
Polyesters produced from microorganisms
Poly(hydroxyalkanoates) (PHAs) form a group which includes poly(hydroxybutyrate) (PHB), a polyester produced from bacteria. Advantages include production from fully renewable ?resources and fast and complete biodegradability. PHAs also have excellent strength and stiffness. However several serious drawbacks hinder their wider application, including brittleness of the material resulting in low toughness (which increases further during storing due to physical ageing), and a high price. PHA’s are biocompatible so could be used in the medical sector. More information can be found on PHAs at the links below http://www.tjgreenbio.com/en/about.aspx?title=About%20GreenBio&cid=25
Manufacturing potential of Biodegradable? polymers
PLA is the most commercialised of all the Biodegradable? synthetics. One of the reasons for PLAs success is that it is it is the only melt-processable fibre from annually renewable ?natural resources. Both Filament? and spun yarns can be produced from PLA. Fabrics produced from spun yarns have a ‘natural’ hand and are considered to feel similar to cotton in this respect. Fabrics from Filament? yarns have a cool and soft hand and exhibit a high fluidity or drape with a degree of Elasticity?. Below is a list of the positive and negative attributes associated with the manufacturing processes and textiles produced from PLA. Although PLA is used as the example, other Biodegradable? textiles would be judged by similar standards-here the key issues to note are in Bold type.
Positive attributes of textiles manufactured from PLA
- The moisture management properties of good wicking, faster moistures spreading and drying mean that garments are comfortable.
- The elastic recovery and Twist? usually intended to be cut or stretch-broken for use in staple fibre or top form.">Tow?.">Crimp? retention properties provide excellent shape retention and crease resistance
- Thermosetting capabilities of the fibre provide for controlled fabric stability, with garments having low shrinkage through repeated washing
- PLA fabrics with no separate flame retardant treatments have passed the US tests 16 CFR 1610 and have also achieved the standards specific for children’s sleepwear, 16 CFR 1615 and 16 CFR 1616.
- The after-care properties of garments in washing are very positive. There is no damage in repeated laundering of PLA fabrics: testing has been carried out under simulated conditions in accordance with AA TCC standards, with no degradation observed.
Negative attributes of textiles manufactured from PLA
There are also certain factors in this relatively early stage of technical and commercial developments that are somewhat restrictive to the development across a full apparel spectrum.
- The melting point of the polymer that are commercially available today is relatively low at 170C. This means that consumer after-care of garments, garment pressing and ironing temperatures have to be lower than the popular fibres of cotton and PET.
- Hydrolytic degradation of polymer can occur, particularly under combined aqueous high temperatures and alkaline conditions; the degree of hydrolysis is influenced by the time, the temperature and the pH. This is particularly significant in in the dyeing and finishing processes, because if the appropriate finishing conditions are not observed it will cause a reduction of the molecular weight of the polymer and therefore the strength of the yarn of fabric.
The range of applications for PLA can be found at: (Click here)