LADY'S FINGER FIBRES FOR POSSIBLE USE AS A REINFORCEMENT

IN COMPOSITE MATERIALS

Md. Moniruzzaman*, Mohd. Maniruzzaman*,M..A. Gafur**, C. Santulli***

* Department of Applied Chemistry and Chemical TechnologyIslamic University, Kushtia, Bangladesh

**Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh

***Department of Electrical Engineering, Università di Roma – La Sapienza, Rome, Italy

SUMMARY

• Lady's finger (okra: Abelmoschus esculentus) fibres

• Chemical treatments and micro-structural effect

• Raw and treated fibres tensile strength

• Okra fibres-bakelite composites: tensile and flexural

strength

• Conclusions

OKRA FIBRES

Raw okra fibresOkra (Abelmoschus esculentus)

Okra (Lady's finger) fibres, extracted from the bark of the okra bahmia plant, aplant of the Malvaceae family, diffused e.g., in North-East India and in the MiddleEast, have an irregular mixrostructure including large lacunae.The main use of okra fibres in materials is as a moisture absorber or a source ofpolysaccharides for possible synthesis of biodegradable polymers with suitablechemical grafting.

CHEMICAL TREATMENTS

Series Chemical treatment

1 None: raw fibres

2 Bleaching with sodium hypochlorite

3 Acetylation with acetic acid

4 Bleaching with sodium hypochlorite + acetylation with acetic acid

5 Treatment with sodium sulphate

6 Bleaching with sodium hypochlorite + treatment with sodium sulphate

7 Alkalisation with sodium hydroxide

8 Bleaching with sodium hypochlorite + alkalisation with sodium hydroxide

One of the problems in using okrafibres is their difficult extraction.There are two aspects whichconcur to the definition of this issue,first the separation of the technicalfibre, and second the “washing out”of non-structural matter,such as wax, pectin, etc.

It is to be demonstrated whetherthe fibre withstand a secondarytreatment after bleaching or if justa primary treatment would bepreferable.

From the initial results, it appears that any treatment is able to ease the separation of the technical fibre, also because okra fibres tend to be only loosely connected after retting.

EFFECT ON THE MICROSTRUCTURE

CONSIDERATIONS ON MICROSTRUCTURE (PRE- AND POST-TREATMENT)

• SEM micrographs of fibres showed a non negligible presence of voids along the fibre length in raw okra fibres. After treatment, the resulting technical fibres have much less scattered diameters.

• However, the results showed that the presence of internal voids was in some cases increased, because of non selective nature of treatment, which degraded lignocellulosic structure as well as "cleaning" the fibres.

• This is particularly true for sodium sulphate treatment and bleaching + alkalisation respectively, whilst the most conservative treatment, leading to lower internal void percentage, appeared to be acetylation.

TENSILE PROPERTIES OF OKRA FIBRES (RAW AND TREATED)

A primary bleaching leads to improved properties of the fibresin most cases, except for the sodium sulphate treatment,where the fibres appear to have been substantially damaged.

TENSILE STRENGTH

Only the introduction of 5% wt. of raw fibres leads to a substantial improvement. A smaller improvement is observed with the same amount of bleached fibres.

FLEXURAL STRENGTH

The trend shown for tensilestrength of raw okra fibre composites can here beconfirmed.Once again, introducing more than5% wt. fibres does not leadto improvement in properties.Also, fibre bleaching leadsto further decrease in compositeproperties.

CONCLUSIONS

• This preliminary attempt of introducing okra fibres in a polymer matrix showed some possible scope only for very low volume (few percents) of reinforcement. Higher volume of reinforcement would result in a difficult resin impregnation, as an effect of the variable geometry of the technical fibre.

• This issue could be solved by appropriate chemical treatment: however, an appreciable improvement has been only shown by fibre bleaching, whilst in other cases the reduced void content, whenever obtained, did not lead to enhanced mechanical properties.

• This implies that a sounder analysis and comparison of the possibilities of chemical treatment on these fibres would be needed, possibly implying different chemicals concentration.