Tuesday 25 February 2014

Wound Care with Photo-active Collagen

More from the EDANA NIA 2013 Conference in Roubaix...

Giuseppe Tronci of Leeds University School of Dentistry described advanced wound care as a $2bn market currently led by hydrogel dressings such as Convatec Aquacel .  These dressings absorb wound exudate to form a protective gel but have several limitations.  They have poor strength when wet and any attempt to increase their strength reduces exudate absorbency.  
They are also based on cellulose which does not promote the healing process as well as collagen.  Unfortunately collagen loses its integrity on extraction from tissues and needs stabilising.  

This is done as follows:

  •         Isolate type 1 collagen from rat’s tails.
  •          Functionalise it using either 4-vinylbenzyl chloride (4VBC) or glycidyl methacrylate (GMA).  These functional groups attach to the surface of the collagen triple helix structure.
  •          UV irradiation of the functionalized collagen causes cross-links to form between the triple helices stabilising the polymer, preventing dissolution and allowing gel formation.
These superabsorbent collagen gels have proved to have better swelling and compression properties than carboxymethyl celluloses, compression at a micro-level having been measured using an atomic force microscope. 

Cytotoxity according to ISO 10993-5 showed that mouse fibroblasts thrived on the gel. For fibre or nonwoven manufacture, the functionalised but unstabilised collagen can be dissolved in water at 40C, wet spun into yarn in a coagulation bath of acetone or methanol, UV-irradiated and stabilized, washed and dried.

Friday 21 February 2014

Composites from Flax and Bio-resins

More from the EDANA NIA 2013 Conference in Roubaix...

Prof. Philippe Vroman of ENSAIT (France) was working on making nonwovens and composites using flax, jute and bio-based materials to replace glass reinforced plastics with green composites.  He explained the terminology:

  •        Biocomposites referred to oil based polymers reinforced with natural fibres, or bio-sourced polymers reinforced with oil-based fibres.
  •          Bio-sourced polymers were those made from starch, castor oil or sugar-cane via ethanol such as PLA, PA11 and PE. 
  •          Green composites were bio-sourced polymers reinforced with natural fibres.
  •          Natural fibres suitable for reinforcement were flax, jute, hemp, sisal, bamboo and kenaf
Commercial examples were from the boating industry:

  •          The “Gwalaz” trimaran based on cork, flax and balsawood reinforced with flax.
  •          The “Araldite 6.5” yacht 50% of which was made from flax-reinforced composites.
  •          The “Plasmor” kayak made from flax/starch-based composite.
Flax was also being used in conjunction with glass and carbon in a variety of sporting goods and automotive panels.

Green composite manufacture involved blending the natural fibres with bio-sourced thermoplastic fibres and compression moulding them to the desired shape.  Physical properties of the composites had been measured in comparison with glass/PP structures.  All the green composites had tensile strength and flexural moduli better than the glass/PP control, with Flax/PA11 proving to be twice as strong.  50/50 Glass/PP had the best impact resistance with the 70/30 flax/PP composite coming a close second.  70/30 Flax/PLA had the best sound absorbency.  However the density of the green composites was generally much higher than the control and the effects of humidity, temperature and UV on the ageing of the green composites had yet to be determined.  In response to questions the other issues in need of further research included “fogging” when used in car interiors, costs of the green composites c.f. current products, appearance of the composites in home furnishing applications, and optimisation of the interface between fibre and resin in each case.

Monday 17 February 2014

Nanostructured Nonwovens with Self-Assembling Peptides

More from the EDANA NIA 2013 Conference in Roubaix...

Robabeh Gharaei of Leeds University (UK) said the materials of the title were being developed as nonwoven scaffolds for tissue engineering.  Such scaffolds had to be highly porous 3D structures which were biocompatible, bioresorbable, biodegradable and had an appropriate surface chemistry.  Examples given included naturally derived polymers such as collagen, chitosan, and elastin or synthetic polymers such as polycaprolactone, polylactic acid or  polyglycolic acid and its copolymers.  These could be 3D printed into the appropriate porous structure, spun into nanofibres, or even simply used as a hydrogel.  Improvements promoting cell attachment, cell proliferation, cell differentiation and extracellular formation were required, and the incorporation of self-assembling peptides within the polymer was thought to be a potential solution.

Electrospun nonwovens have therefore been made from 6% PCL in hexafluoro-2-propanol loaded with the peptides P11-4 and P11-8, both of which were bioactive and specially synthesised for use in nonwoven scaffolds.  Concentrations of 20 and 40g/l of the peptides in the dope were used and both caused the production of a biphasic structure (a mixture of filaments and short submicron fibres).  ATR-FTIR analysis of the fibres showed the presence of both monomeric and beta-sheet peptide structures. It was postulated that the peptides were self-assembling into “beta-sheet tapes” during spinning and causing this mixture. 

Asked if the biofunctionality of these nonwovens had been checked, Ms Gharaei said they hadn’t but she expected to see improvements over the current scaffolds.  The peptides did not self-assemble in solution so it must be happening during spinning.  Maybe the peptide is affecting the surface tension of the dope and thereby affecting the resulting fibres.

Thursday 13 February 2014

Nonwovens containing Methylglyoxal for Wound Care

More from the EDANA NIA 2013 Conference in Roubaix...

Sophie Bulman of Leeds University (UK) thought dressings which used Manuka Honey to increase the rate of healing of chronic wounds owed at least some of their success to the methylglyoxal content of the honey.  Infections in chronic wounds were resistant to antibiotics and while some treatment success was claimed for silver impregnated dressings, bacteria were now evolving with silver resistance also.  Alternative metals e.g. zinc and naturally derived antibacterials such as Manuka honey were therefore being evaluated.  Alginate nonwovens, knitted viscose and non-fibrous hydrocolloids were all being used as substrates for the honey but it was a difficult material to handle due to its stickiness, could cause skin rashes and was not suitable for use on the open wounds of diabetics.

Manuka honey was compared with the equivalent amount of methylglyoxal as an antimicrobial finish on textiles using ISO 20743:2007 and found to be similarly effective.  PP spunbond nonwovens samples were then coated either by electrospraying  a water-based solution of 8% PVA loaded with  11% MG, or electrospinning the same solution into a web of nanofibres.  Both methods were intended to give the maximum possible surface area.  FTIR and NMR analysis proved the PVA nanofibres contained MG. The samples were then tested using the zone of inhibition method on agar plates colonised with E. coli and S. aureus bacteria according to ISO 20645:2004.  The controls (spunbond with no MG) showed no zone of inhibition, whereas the spunbond electrosprayed with MG showed zones of 4mm for E. Coli and 6mm for S. Aureus.  The MG/PVA nanofibre coats were even more effective showing inhibition of bacterial growth up to 20 and 21mms respectively.  Asked how much MG was required to render the nonwoven antimicrobial Ms Bulman said 1mg/cm2.

Monday 10 February 2014

PP nonwovens containing non-encapsulated PCMs

More from the EDANA NIA 2013 Conference in Roubaix...

Waclaw Tomaszewski of the Institute of Biopolymers and Chemical Fibres (Poland) described the uses of Phase Change Materials in regulating the temperature of buildings (in insulation) and people (in clothing).  These chemicals absorb heat on melting and release it again on freezing and can be tailored to work at specific temperatures, e.g 220C for building insulation and 370C for clothing.  Unfortunately the PCMs are normally supplied as microcapsules and these increase the costs of products made from them, restrict the concentration in fibre to about 10% and prevent their use in fine-fibre products such as meltblown.

In this project, 4 different PCMs (all paraffin waxes) were added to PP and pelletized.  Not all the wax co-crystallized with the PP: e.g. from a 30% addition only 20% remained fixed in the polymer.  Further losses occurred due to evaporation of some of the wax from some of the PCMs during melt blowing, but meltblown PP webs containing 20% PCM were produced and tested.  Thermal imaging and measurements of temperature regulation factors showed that the PCMs were working as expected although the rates of heating and cooling affected their performance.  They worked better with gradual temperature changes.  Thermal wave propagation measurements showed that for rapid temperature changes only the PCM in the layer close to the heat source was effective. 

In response to questions Mr Tomaszewski revealed that the PCM tended to be at the surface of the fibre and could be removed by washing.  One questioner proposed using the PP/PCM pellets for the core of a bico fibre.

Saturday 8 February 2014

Laser-bonded Electrospun Nonwovens

More from the EDANA NIA 2013 Conference in Roubaix...

Christoph Hacker of RWTH Aachen University (Germany) observed that the electrospun webs needed to improve the filtration efficiency of drinking water filters are very fragile and therefore hard to laminate to stronger meltblown or spunbond nonwovens.  They are easily destroyed by hydroentanglement, needlepunching or thermal bonding, and the use of lasers alone fails because the polymers do not absorb laser energy.  The solution is to electro-spray submicron droplets of an energy absorber onto the substrate before electrospinning the fibrous layer, and for the purposes of these experiments the droplets contained carbon black to indicate how uniformly the spot-bonds were distributed.

The beam from a 100watt diode laser was spread using a prism to 35mm wide and as the laminate containing the droplets – held under pressure beneath a glass plate - was illuminated by it, the droplets heated up and spot-bonded the layers together without destroying any of the electrospun filaments.
Microscopy and peel strength tests showed the bonding process was successful and filtration testing showed that the bond points did not affect filtration efficiency.

Work continues to convert this batch demonstration process into a continuous process with wider lasers, simultaneous electrospinning and electrospraying, and a search for improved energy absorbers.  Mr Hacker thought the process might ultimately run at 10m/min.

Sunday 2 February 2014

Hydroentangled Air-laid flax Nonwovens

More from the EDANA NIA 2013 Conference in Roubaix...

Philippe Mesnage of ITFH (France) is evaluating hydroentanglement as an alternative to needlepunching for making flax nonwovens for composite reinforcement. The raw flax contains ~70-75% cellulose with 10-15% of hemicellulose, 3-5% lignin and a similar proportion of pectins. Mechanically refined flax (MRF) tows were cut into lengths of 25-35mm for airlaying and compared with a more fully refined 45mm flax intended for spinning into yarns (SF). MRF was coarse – 34 to 90 on the IFS scale (Flax Standard Index) compared with 20-30 IFS for the SF fibres. These long fibres clogged the air-lay drums and further work was carried out with fibres chopped to 15mm which could be successfully laid into ~150gms sheets.

After hydroentanglement, nonwoven tensile strengths were highest for the SF fibres (358N/5cm) compared with 215N/5cm for the best of the MRF.  Tear strengths were however comparable, presumably due to the higher denier of the MRF.  The extra stiffness of the MRF samples was not just down to the coarser fibres.  Mr Mesnage thought the non-cellulose components of the fibre were being solubilised in hydroentanglement and acting as a chemical binder.  Asked what advantages this route might have over the needlepunched route he thought there was a potential for higher productivity from the faster laying and bonding machinery and added that the end product was completely natural, made in the EU and used no added binders.

Saturday 1 February 2014

The Flexibility of Life Cycle Analysis

Adrian Wilson's paper on Life Cycle Analysis presented at INDA's Vision Conference in Dallas by Calvin Woodings on 30/1/2014 follows in full.

Life cycle assessment (LCA) is increasingly being applied to support public policy making, to the consternation of some researchers and practitioners.

Initially during the 1990s LCA methodology helped to develop eco-labels and certification schemes, evolving to inform policy documents and eventually packaging legislation in Europe. It was also employed to guide alternative-fuel policies in the US.

LCA has continued to gain ground in the 21st Century and was incorporated into the ‘Integrated Product Policy’ of the European Union (EU). It was also intrumental in the establishment of several life cycle-based carbon footprint standards and regulations for transportation fuels in the US, EU and Canada.

Critics, however, have started to question the validity and usefulness of results from LCA.

The many studies on disposable and reusable diapers have been held up as a prime example of how widely varying conclusions can be drawn from LCA comparisons of competing products.

But it is especially the use of LCA findings to make performance-based regulations (PBRs) – such as in the European Renewable Energy Directive (RED) relating to biofuels – that the most concern has been voiced.