Monday, 19 November 2007

A resurgence of regenerated cellulosics.

In the last 2 years, massive expansions in viscose production, and the pulp required to produce it have been announced – totalling in excess of half a million tonnes of new fibre. Surprisingly none of the expansion involves the more eco-friendly lyocell route. In the absence of this new capacity, viscose and lyocell prices have risen sharply and the market is currently undersupplied due to high demand in textiles as well as nonwovens. The world’s leading producer, Lenzing is enoying full production and good prices. 2007 will be its best year ever, and they are leading the expansion.

(Source: The Saurer Report 2006-7)
Research into cellulose and its derivatives is increasing. To take a few highlights from recent conferences:
  • Processes potentially capable of giving low cost cellulosic nonwovens are now being evaluated on a pilot scale at TITK and Fraunhofer.
  • At TITK, Lenzing and Nanoval are co-operating to produce a “melt-blown” version of lyocell using the Laval nozzle to split the fibres into micro-fibres.
  • At Fraunhofer, Weyerhaeuser and Reicofil are using a 60 cm Reicofil melt-blowing nozzle as a spinnerette to produce spun-laid lyocell.
  • These processes work with low-quality dope from paper-pulp and the cellulose can be more easily alloyed with high levels of other materials such as PP.
  • Ionic liquids have made dopes with 20% cellulose from which Tencel-like fibres and alloys with other polymers have been spun on lyocell pilot equipment.
  • 30% solutions of cellulose carbamate in NMMO have been converted to fibers with tenacities above 60 cN/tex. (These solutions are anisotropic above 20%)
  • Cellulose nanofiber fiber webs for use in medicine and cosmetics have been produced by the surface culture of bacteria.
  • Cellulose nanofiber webs made by electrospinning appear to have a total free absorbency of 2000 gms/gm.
  • Work continues on the dissolution of enzyme degraded cellulose directly in caustic soda.
Could cellulosics really replace polypropylene as the workhorse fibre for disposable nonwovens?
As we have seen, the ecological logic is sound:
  • Cellulose is the only really abundant fibre-forming polymer produced and disposed within the carbon cycle. (but don’t forget alginic acid and chitin remain to be fully exploited.)
  • Pure cellulose in the form of cotton, grown organically maybe in Africa, has the least environmental impact of any fibre and would be a low-cost yet valuable crop.
  • If cellulose must be grown on land which can not be used for food crops, it must first be pulped, dissolved and regenerated to form useable fibres.
  • Numerous processes exist for making cellulosic fibres from biomass, and all are potentially carbon-neutral because the parts of the biomass unsuitable for including in the finished fibres can be used to power the pulping, dissolution and fibre spinning operations.
  • Existing dry-lay, wet-lay and air-lay nonwoven process could convert these fibres into nonwovens provided hydroentanglement is the bonding system.
  • Surface acetylation of cellulose fibres can allow some thermoplasticity for thermal bonding purposes if the extra small monetary and ecological expense can be justified. (Acetic acid is a by-product of the pulping operation.)
  • Cellulose can be spunbonded, literally, in various ways to make self-bonded nonwovens, or spun laid where hydroentanglement would be the bonding mechanism of choice.
  • Assembling finished disposables without the help of thermoplasticity would be tricky, but fabrics can be glued or even stitched together – by computer-controlled high pressure water needles - in the same way as these needles at even higher pressure are used as cutters.
  • Cellulosic fibres can be converted into superabsorbents, and such products are already used in wound care. (Cellulosic nonwovens could be treated on one side to form a self-sealing breathable backsheet.)
  • Cellulosic disposables would be fully compatible with sewage systems, especially if the fibres are short and lightly bonded, or if the products are shredded through a waste disposal unit attached to the toilet.
As an aside here, any biodegradable waste could be disposed of through shredders into the sewage system and anaerobically digested at the sewage farm to yield methane for power generation.
  • Maybe as new infrastructure is developed and old infrastructure renewed, the installation of this option would take a load off landfill and the reduce the environmental costs of collecting and transporting rubbish from homes to landfill or aerobic composters.
  • If organic matter – including urine and faeces – could be kept out of the solid waste, the collection of the remaining rubbish could be very infrequent.
  • The life cycle analysis of the disposable diaper could be improved. Diapers would be credited not just with the energy generated from their mainly cellulose construction but also with that from the excrement they have saved from the landfill.

In Conclusion

For the last 40 years, the dramatic growth of the nonwovens and disposables industry has depended on increasing use of fossil reserves. Consumers have accepted convenience products based on unsustainable, non-biodegradable materials requiring landfill disposal. Climate change and its effects are changing consumers attitude to disposables and the continuing oil supply/demand imbalance will encourage a reversion to polymers from biomass. Flushable disposables based on cellulose would be sustainable, and recyclable to energy in sewage treatment.
Calvin Woodings

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