Modification
of Jute Fiber
The development of
environment-friendly green materials is because of natural fiber’s
biodegradability, light weight, low cost, high specific strength compared to
glass and carbon, recycling and renewing natural sources. The jute fibre is an
important bast fibre and comprises bundled ultimate cells, each containing
spirally oriented micro- fibrils bound together. The primary component of the
fibre is cellulose, which is a linear condensation polymer consisting of
Danhydroglucopyranose units joined together by β-1, 4-glucosidic bonds. The
major part of the cellulose consists of a microcrystalline structure with high
order of crystalline regions. Other components of the jute fibre are
hemicelluloses, lignin, pectin, waxy and water soluble substances. Because of
the structural features, the high level of moisture absorption and poor
wettability of the natural fibre material results in insufficient adhesion
between fibres and polymer matrices leading to debonding during use and aging.
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| Jute Composite |
In order to develop composites with better mechanical properties and environmental performance, it is necessary to impart hydrophobicity to the fibres by chemical reaction with suitable coupling agents or by coating with appropriate resins. Such surface modification of jute fibre would not only decrease moisture adsorption, but would also concomitantly increase wettability of fibres with resin and improve the interfacial bond strength, which are critical factors for obtaining better mechanical properties of composites. The modification is required to improve the wettability and compatibility of the fibre with resin matrix to produce strong fibre-matrix interface. Modification can be done in three different ways.
i)
Physical modification
Different
physical treatments like boiling of fibre with or without pressure, plasma
treatment etc can improve the cleaning of fibre surface which can react with
resin easily to form a strong interface. Polymeric coatings of jute fibre with
phenol-formaldehyde or resorcinol formaldehyde resins by different approaches
are highly effective in enhancing the reinforcing character of jute fibre,
giving as high as 20-40% improvements in flexural strength and 40-60%
improvements in flexural modulus. These modifications improve the fibre-matrix
resin wettability and lead to improved bonding.
ii)
Chemical modification
The
chemical modification involves mainly etherification, etherification,
cyanoethylation, grafting etc. All these chemical reactions involve mainly the
hydroxyl groups of the fibre and the modified fibre develops certain
characteristics like low moisture regain, improved compatibility with resin
etc. Jute is chemically treated with isopropyl triisostearoyl titanate
(abbreviated as titanate), g - aminopropyl trimethoxy silane (abbreviated as
silane), sebacoyl chloride (SC), and toluene diisocynate (TDI). All these
reagents are expected to block the hydroxy groups of jute thus making the
fibres more hydrophobic.
iii) Graft
copolymerisation.
Jute can
be graft copolymerised with vinyl monomers such as methyl methacrylate, ethyl
acrylate, styrene, vinyl acetate, acrylonitrile and acrylamide in the presence
of different redox initiator systems such as vanadium - cyclohexanol, vanadium
- cyclohexanone, etc. Grafting of polyacrylonitrile (10-25%) imparts 10-30%
improvements in flexural strength and flexural modulus of the composites.
Grafting of polymethylmethacrylate is also effective in this respect, though to
a lower degree.
iv)
Bio-chemical modification
Grey jute
fibre contains some natural as well as added impurities, which needs to be
cleaned for making jute fibre suitable for composite preparation. Moreover,
removal of some amount of hemicelluloses as well as lignin makes the fibre more
suitable for its compatibility with resin, which ultimately results in better
jute reinforced products. Several processes have been tried on jute fibre,
which include scouring, bleaching, enzyme treatment, alkali treatment,
thermo-hydrolysis etc. to improve its adhesion with resin. These modification
processes also lead to some reduction in its tensile property but if the
treatments are carried out at optimum conditions the composites produced shows
improved tensile as well as flexural behaviour
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