WVTR of bio derived composite resins  

Posting by brooke jenkins on June 17, 2008 at 18:43:46.

To All:

Nowadays bio-derived composite resins - like polylactide and furan based resins - combined with natural flax (obtained from bast) fibres - rather than petrochemical-based products - is a hot topic. It is stated that material properties are rather promising, not only because of environmental friendly disposal, but also because of intrinsic flax performance. For example: it is told that natural flax fibres have a comparable strength and equal fire-resistance properties and that they are 10-30% lighter than glass fibres (no doubt about that). Assuming that limitations in processing technologies and molded part performance will be overcome within a relative short term (also with support from the European Union, see the recently commenced Biocomp project), my interest is the mechanical and chemical retention of the following materials when exposed to a water vapour (moisture humidity 0 to 100% at ambient conditions):

- Ciba Geig LY556 Epoxy Resin reinforced with 50 wt% natural flax fiber;
- Polylactide based resin with 20 wt% natural flax fibre;
- Furan based resin with 20 wt% natural flax fibre.

How does this compare to the diffusion, permeation and corrosion behaviour of similar resins reinforced with glass fibres? And how about Interlaminar shear strength (ILLS) of flax and resins considered, in humid conditions compared to glass fibre reinforced polymers?

Brooke Jenkins

p.s. what about the long term water vapor transmssion rate (WVTR) of these bio composites; are they comparable to the WVTR of say a 35 volume percent glass reinforced commonly used GRP, say polyester, bisphenol A or phenolic epoxy material?

          follow up posts
    On 06 Jan 2009 at 21:35:15 Brooke Jenkins posts:
    Hi all,

    I am still interested in the chemical and long term mechanical properties of biocomposites, especially in a long term humid environment (80%, 90%, 100% of moisture). Specific interest are the following biocomposite formulations:

    - Polylactide based resin with 20 wt% natural flax fibre;
    - Furan based resin with 20 wt% natural flax fibre.

    Some basic information like water WVTR, diffusion coefficient, water solubility, resin - flax interface behaviour and retention of Young modulus is already worthful, since I can not find a lot of chemical-physical property information on the bio composites described.

    Thanks in advance for your remarks and comments!

    Brooke Jenkins
    [responses: 3]
      On 07 Jan 2009 at 10:30:57 Mark van Brakel posts:
      Interesting question.

      Currently in The Netherlands there are some green biocomposites projects going on. One involves the projected future replacement of steel by a biocomposite nose and real panels of the Dutch InterCity trains. The bio composite contains natural fibres, probably flax fibres, and ordinary high fire resistant resin. The suggested "bio solution" has lower weight and is more environmental friendly since it does not contain glass fibres. The overall long term physical properties - very probably also including the water permeation diffusion resistance of the flax - resin combination - are currently still subject to research. The Dutch composite manufacturer company NPSP Composieten B.V. will manufacture the biocomposite train nose panels.

      Yesterday I read that NPSP Composieten will also produce green automotive components, as to be used in cars, scooters etc.

      [responses: 2]
        On 08 Jan 2009 at 16:51:42 Composite Agency posts:
        Thanks Brooke and Mark:

        Natural fibres, like flax and hemp, have a relative high strength and stiffness to weight ratio, relative high toughness, good thermal properties and are biodegradable. However there are some challenges in the practical use, which is an intrinsic poor compatibality between the fibre and several matrices, including pe, pp, vinyl ester, epoxy and polyurethane resin materials and inherent high moisture uptake and subsequent swelling of the flax (or hemp which is also used).

        At 23 degrees Celsius, the 100% moisture absorption of most low or medium hydrophobic polymers - including pe, peek, polyimide and epoxy resins - is below 1%, whereas the water solubility in flax is approx. 7% (hemp approx. 8%).

        Whether this behaviour is a problem depends - i.e. leads to cracks and undesired dimensional composite change - on many factors. Mentioning a few: the laminate build-up, the chemical treatment of the fibres (alkali / acid), the resin used, the dual mode diffusion and sorption character, and the dimensionnal shape of the final application.

        The best option is to simulate the laminate by the CheFEM software, also before commencing with any laboratory experiment. Be warned that accelerated testing (high temperature to make use of time-temperature superposition) will very probably produce incorrect results. Note that the limited use of (hydrophilic) Kevlar as composite reinforcement has also been partially due to misinterpretation of water update behaviour and incorrect accelerated laboratory testing.

        Composite Agency Team
        [responses: 1]
          On 29 Jan 2009 at 09:43:02 Brooke Jenkins posts:
          Many thanks so far.

          Could you produce the water or vapour diffusion / permeation concentration profile and mass transfer for the flax - epoxy bio composite for a laminate consisting of 3 different plies? I remember this was once done for the water vapour transmission rate (WVTR) determination of GRP consisting of glass veil, chopped strand mat and a woven roving layer, after they had performed ASTM E96 and ASTM D570 laboratory tests for each layer seperately. The appplication is a cubic composite container for an electronic device.

          [responses: 0]

    On July 01, 2008 at 10:05:35 Lutz Meyer posts:
    I would like to add a similar question with regard to ageing of windmill composite under mechanical stress and salt water exposure.
    What is the influence of salt water on the long term service life of blades made from unsaturated polyester or epoxy resin reinforced with glass fibre in the severe stress conditions. Is exposure to salt water more severe than demineralized or "normal" water, especially in case of mechanically unstressed and stressed state? Does a modest strain modify the permeability rates of a composite material?

    Secondly, is flax reinforcement an option for windmill blades? Are bio reinforcement or bio polymers currently applied in the windmill farms on sea in Germany, Denmark or Netherlands?

    Lutz Meyer

    [responses: 1]

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