Studies on Swelling Propertiesof Wood/Polymer CompositesBased on Agro-Waste andNovolac

S. MISHRA, J. B. NAIK, Y. P. PATILUniversity Department of Chemical Technology, North Maharashtra University, Jalgaon 425 001,Maharashtra, India

Received: September 19, 2000Accepted: October 6, 2003

ABSTRACT: In the present work the natural and maleic anhydride esterifiedfibers of banana, hemp, and sisal are used as reinforcers in novolac resin in theratio of 40:60 (wt/wt), respectively. Absorption of water and steam in thesewood/polymer composites is studied. The absorption of water increases withincrease in time from 2 to 30 h in all fiber composites tested. Amongst all thecomposites, the maximum absorption of water is found in hemp fiber compositeand the minimum in maleic anhydride treated sisal fiber composite. The maleicanhydride esterified fiber composite shows less absorption of water than theuntreated fiber composites. Amongst all six composites, steam absorption ismaximum in untreated hemp fiber composite and minimum in maleic anhydridetreated banana fiber composite. Steam absorption in maleic anhydride treatedfiber composites is higher than the water absorption in respective fibercomposites. Untreated fiber composites show more absorption of steam incomparison to maleic anhydride treated fiber composites. C© 2004 WileyPeriodicals, Inc. Adv Polym Techn 23: 46–50, 2004; Published online in WileyInterScience (www.interscience.wiley.com). DOI 10.1002/adv.10073

KEY WORDS: Composites, Natural fibers

Correspondence to: S. Mishra; e-mail: profsm@rediffmail.com.

Advances in Polymer Technology, Vol. 23, No. 1, 46–50 (2004)C© 2004 Wiley Periodicals, Inc.

SWELLING PROPERTIES OF WOOD/POLYMER COMPOSITES

Introduction

T he increasing demand for wood, resulting indeforestation, is a great threat to society. Be-

cause of lack of suitable technology for the effi-cient utilization of agricultural waste and forestryresidues, this precious wealth goes to waste andthe net impact is the deforestation, which causesenvironmental erosion. Therefore this is the needof the hour to develop appropriate technology forutilization of agro-waste. Polymer technology maybe applied to utilize wood, agricultural waste, andforestry residues. Further exploration of this technol-ogy is highly demanded as the product developedfrom the forestry residue is economical, dimension-ally stable, possess longer life, and also provides pro-tection to the environment by checking deforesta-tion.

Certain physicochemical properties such as den-sity, swelling, and mechanical properties are knownto be affected by the presence of varying quantitiesof moisture in the fiber. Mukherjee1 has reported therole of moisture in textile fibers. Many workers2−9

have reported the effect of moisture on the mechan-ical properties of polymer composites. Because ofthe incompatibility of moisture with fibers, compos-ites made from fibers of high moisture content mightexhibit voids or porosity. As a result fiber to ma-trix adhesion is poor, causing deterioration in thecomposite properties. Rao et al.10 have reported thetechniques of reducing moisture absorption in jute-epoxy composite.

In view of the adverse effect of moisture on prop-erties of natural fiber based polymer composites, thepresent study reports on the effect of steam and wa-ter absorption (swelling properties) in six differentcomposites based on novolac reinforced by (i) ba-nana fiber (ii) hemp fiber (iii) sisal fiber and maleicanhydride treated/esterified fibers of (iv) banana (v)hemp, and (vi) sisal.

Experimental

MATERIALS

Chemicals

Phenol, formaldehyde, oxalic acid, xylene, andmaleic anhydride used were manufactured and sup-

plied by S. D. Fine Chemicals Ltd. Mumbai, India.Hexamethylene tetramine used was manufacturedand supplied by Loba Fine Chem, Mumbai, India.

Fibers

Natural (untreated) fibers were obtained from thestems of banana, hemp, and sisal. The fibers wereesterified using maleic anhydride (MA).

The banana, hemp, and sisal fibers were obtainedfrom the raw material by the process of retting. Thesefibers were dried in oven at 60◦C and cut into 2.0–2.5 mm lengths. The fibers were esterified using 2%MA in xylene. The soaking of MA was allowed for18 h. The fibers were filtered out and dried in ovenat 60◦C till fibers showed constant weight.

MATRIX RESIN

The novolac resin prepared11 in the laboratory byusing phenol and formaldehyde in the ratio 1:0.83in the presence of oxalic acid (1.5% of phenol), wasground as fine powder.

PROCESSING OF COMPOSITES

The fiber and novolac resin were taken in the ra-tio of 40:60 wt/wt and mixed in a powder blender atambient (27◦C) temperature for about 10 min. Fur-ther, the blended material was fed on to a heatedtwo-roll mill and mixed for 5 minutes at 100 ± 2◦C.“Hide” from the mill was then cooled and pulver-ized. Hexamethylene tetramine (12% of resin) andcalcium oxide (3% of resin) used as curing agent andactivator, respectively, were mixed in the pulverizedmaterial.

SAMPLE PREPARATION

The pulverized material was molded into 2-mmthick sheets by using a compression molding ma-chine, at temperature 165 ± 5◦C for 4 min while ap-plying pressure in increments of 4.8, 9.8, 14.7, and19.6 MPa for a duration of 1 min each. The mold wascooled under pressure by circulating cold water andthe sheet was removed from the mold after releasingthe pressure.

WATER AND STEAM ABSORPTIONSTUDIES

The wood/polymer composites were swollen inwater at ambient temperature and in steam for

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2–30 h. For this study the samples of dimensions 0.5× 1.0 × 10.0 cm3 were used separately. For waterabsorption studies, the samples were submerged instagnant distilled water having pH 7.0. For steamabsorption study, the samples were hung in a closedwater bath provided with heater system to boil thewater continuously. The samples were surface driedusing blotting paper after water and steam absorp-tion. Change in weight was recorded using electronicbalance having a least count of 0.1 mg.

Results and Discussion

Absorption of steam in wood/polymer compos-ites of novolac and MA treated and untreated ba-nana, hemp, and sisal fibers: the six wood polymercomposites made from novolac reinforced by MAtreated and untreated banana, hemp, and sisal fiberswere studied for steam absorption for 2–30 h. Fig-ure 1 shows that the absorption of steam increaseswith increase in time from 2 to 18 h in all the sixcomposites. Beyond 18 h no additional absorptionof steam is found in any of the six composites.

FIGURE 1. Comparison of absorption of steam inbanana, hemp, and sisal fiber composites with andwithout treatment with maleic anhydride.

Amongst the composites based on novolac rein-forced by natural (untreated) banana, hemp, andsisal fibers, after 24 h exposure to steam, hempfiber composites show a maximum (29.3%) steamabsorption and sisal fiber composites show a mini-mum (20.5%) steam absorption, while banana fibercomposites show intermediate absorption of steam(25.5%). Amongst the composites based on MAtreated (esterified) fibers, after 24 h exposure tosteam, hemp fiber reinforced novolac shows maxi-mum steam absorption (19.5%), banana fiber rein-forced novolac shows minimum steam absorption(16%), and sisal fiber composite shows intermediatesteam absorption (16.5%) although that is marginallyhigher than the moisture absorption by banana fibercomposite.

The MA treated fibers based composites showvery less absorption of steam compared to respectivenatural (untreated) fiber reinforced composites. It isobserved from the results that the steam absorptionis minimum in the MA treated banana fiber compos-ite while untreated hemp fiber composite shows themaximum absorption of steam.

In all six composites the rate of absorption ofsteam decreases with increase in time up to 18 h; be-yond this period of time no additional absorption ofsteam is observed up to 30 h (Fig. 1). All six compos-ites based on novolac reinforced by maleic anhydride(MA) treated and untreated fibers show drastic re-ductions in the rate of absorption of steam after 12 h.exposure and do not show any additional steam ab-sorption after 18 h.

Absorption of water at ambient temperature inwood/polymer composites of novolac reinforcedby MA treated and untreated banana, hemp, andsisal fibers: Fig. 2 shows the results of water ab-sorption at ambient temperature by all six com-posites of novolac reinforced by MA treated anduntreated banana, hemp, and sisal fibers. It is ob-served from Fig. 2 that the absorption of water in-creases with increase in time in untreated and MAtreated fiber composites. Amongst the compositesbased on novolac reinforced by natural (untreated)banana, hemp, and sisal fibers, the untreated hempfiber composite shows maximum absorption of wa-ter (19.5%) at ambient temperature, untreated sisalfiber composite shows the minimum absorption ofwater (11%), and the absorption of water in untreatedbanana fiber reinforced novolac composite (13%) isintermediate between these two fiber compositesfor the entire period of time. Amongst the compos-ites based on MA treated fibers, water absorptionis maximum in MA treated hemp fiber composites

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FIGURE 2. Comparison of absorption of water inbanana, hemp, and sisal fiber composites with andwithout treatment with Maleic anhydride.

(14.5%), minimum in MA treated sisal fiber compos-ites (9.5%), and MA treated banana fiber compositeshows intermediate water absorption (10.5%).

From these results it is found that the MA treatedfiber composites show lesser absorption of waterthan the untreated respective fibers composites.

It is very clear from Fig. 2 that the rate of absorp-tion of water is highest in the first 2 h in all thesefiber composites. The rate of absorption of water inMA treated fiber composites is less than that in therespective untreated fiber composites.

MECHANISM OF STEAM AND WATERABSORPTION

As discussed in our earlier work12,13 the MA ester-ifies the free OH groups present in banana, hemp,and sisal fibers, and that reduces absorption of wa-ter and steam in composites. Amongst all six com-posites, absorption of water and steam is maximumin untreated hemp fiber reinforced novolac compos-ite due to the maximum (98%) number of free OHgroups in the hemp fibers. Sisal fibers contain theminimum (48.3%) free OH groups that are ester-ified upon MA treatment, hence MA treated sisal

fibers reinforced novolac composites shows mini-mum absorption of water.

Steam penetrates more in comparison to wa-ter, therefore results in more absorption. Waterpenetrates slowly and to a lesser extent thansteam, which results in less absorption of water bycomposites.

Conclusions

The following conclusions can be drawn from thisstudy.

1. The absorption of water and steam increaseswith increased time in all the six fiber compos-ites.

2. No additional absorption of steam is observedafter 18 h exposure in untreated and MAtreated fiber composites of the respective fibers.

3. The absorption of steam is maximum innatural (untreated) hemp fiber compositesand minimum in MA treated banana fibercomposites.

4. The absorption of water is the maximum in un-treated hemp fiber composites and the mini-mum in MA treated sisal fiber composites.

Acknowledgments

The authors are deeply grateful to the reviewersfor their comments.

References

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