Indian Journal of Fibre & Textile Research Vol. 25, December 2000, pp. 295-297

Chemical resistance and tensile properties of epoxy/polymethyl methacrylate blend coated bamboo fibres

A Varada Raj ulua, G Babu Rao & R Lakshminarayana Reddy Department of Polymer Science & Technology, Sri Krishnadevaraya University, Anantapur 5 1 5 003, India

Received 18 January 2000; accepted 22 February 2000

The untreated and I % aqueous NaOH treated bamboo fibres (Dendrocalamus strictus) were coated with epoxy, polymethyl methacrylate (PMMA) and their blends. The chemical resistance of these fibres to acetic acid, nitric acid, hydrochloric acid, sodium hydroxide, sodium carbonate, ammonium hydroxide, benzene, toluene and carbon tetrachloride was studied. It has been observed that the uncoated fibres dissolved completely in nitric acid, while the fibres coated with epoxy, PMMA and their blends were resistant to all the acids and alkalis studied. The fibres coated with PMMA and blend of epoxy/PMMA showed a decrease in weight when immersed in the solvents, indicating that the coated fibres are not resistant to the solvents. The coated fibres show lower water absorption as compared to the uncoated fibres. The tensile load-at-break of the epoxy/PMMA coated fibres is higher than that of the uncoated, PMMA-coated and epoxy-coated fibres. These observations indicate that the bamboo fibres and the PMMAIepoxy blend are suitable materials for making composites having better tensile properties and chemical resistance to acids and alkalis.

-Keywords: Bamboo fibre, Epoxy/PMMA blend, Epoxy resin, Polymethyl methacrylate, Tensile load

1 Introduction Several studies on the composites made from

thermoset materials and natural fibres l ike jute, wood, bamboo, sisal , cotton, coir, wheat straw, etc. have been reported 1 -7. For making the natural fibres reinforced plastics, suitable matrix materials are to be identified. It is, therefore, customary to test the performance of the matrix-coated fibres and if they show improved properties, then the system can be recommended for making the composites. Recently, Varada Rajulu et ai .8.9 studied the chemical resistance and tensile properties of epoxy and styrenated . polyester coated bamboo fibres and suggested that these are favourable materials for making the composites. For toughening of epoxy resin, the thermoplastics, such as polymethyl methacrylate 10 and pol ycarbonate I I , were added and these blends were found to possess better properties than the thermosets. Though the bamboo is extensively used as a valuable material from times immemorial (because of its high strength - to - weight ratio), the studies on these fibres are meager. In the present study, bamboo fibres were coated with epoxy, PMMA and epoxy/PMMA blends and their ' chemical resistance and tensile properties

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studied to ascertain whether the epoxy/PMMA ­bamboo fibres system can effectively be used for making the composites.

2 Materials and Methods

2.1 Materials

2.1.1 Bamboo Fibres

Bamboo fibres (Dendrocalamus strictus), procured from Tripura in the dried form, were soaked in 1 % NaOH solution for 30 min to remove greasy material and lignin from the fibres9. These fibres were then washed thoroughly in distilled water and dried under the Sun for two weeks. The length of the fibres was found to be 22cm and the fibre cross-section was rectangular with breadth and thickness varying from 0. 1 to 0.6mm. The fibres with a thickness of 0.2mm were selected for the study. For studying the tensile properties and chemical resistance, the fibres were cut to 1 5cm and 2cm lengths respectively.

2.1.2 Chemicals

Glacial acetic acid, conc. mtnc acid, conc . hydrochloric acid, conc. ammonium hydroxide, aqueous sodium carbonate (20%) and aqueous sodium hydroxide (60%) were used.

The resin matrix system (Araldite L Y 5052/hardener HY 5052), supplied by Mis Hindustan Ciba- Geigy,

296 INDIAN J. FIBRE TEXT. RES. , DECEMBER 2000

was used. PMMA with a number average molecular weight of 98,000 (supplied by MIs GSFC, Baroda) was used.

For making the blends having 2.5%, 5%, 7 .5%, 10%, 1 2.5%, 15% and 1 7.5% of PMMA, 10% PMMA solution in toluene was added to the resin (L Y 5052) in appropriate volumes. The mixture was then kept in vacuum until the entire solvent got evaporated. To this mixture, the required quantity of hardener HY 5052 was added and mixed thoroughly.

2.2 Methods

2.2.1 Sample Preparation

For tensile strength, the fibres soaked in the epoxylPMMA blend were vertically hanged to a wooden frame and kept in a vacuum oven at 65 DC for 1 2h to complete the curing. For chemical tests, the short fibres were soaked in the resin mixture. The excess resin was removed by placing the fibres i n the vertical position. The fibres were then placed on glazed polyester sheet and cured as described above.

2.2.2 Measurement of Tensile Load

The tensile load-at-break of the coated and uncoated bamboo fibres was determined using Mikrotech Tensometer employing disk wire chucks. Ten samples were tested in each case and the average tensile load was determined.

2.2.3 Measurement of Chemical Resistance

The chemical resistance of the bamboo fibres with and without coating of epoxylPMMA blend was studied as per ASTM D 543-87 method 1 2. In each case, ten pre weighed samples were dipped in the respective chemicals for 24h, removed immediately, washed with distilled water and then dried by pressing them between the filter papers. The samples were then weighed and the percentage weight loss/gain was determined.

3 Results and Discussion Using viscosity, ultrasonic velocity and refractive

index, Varada Raj ulu et aZ1 3 .found that the blend of epoxylPMMA is immiscible. The values of average tensile load-at-break of the bamboo fibres before and after coating are given in Table 1 . It i s clearly evident that the tensile load is low for the uncoated fibres (7.62 kgf) whereas i t i s high for epoxylPMMA blend coated fibres. However, for the fibres coated with epoxy and PMMA, the increase in tensile load over the uncoated fibres is found to be only 10% and

Table 1 - Tensile load-at-break of uncoated, epoxy coated, PMMA coated and Epoxy/PMMA blend coated bamboo fibres

Fibre

Uncoated

Epoxy/PMMA blend coated 2.5" 5.0" 7.5" 1 0.0" 1 2.5" 15 .0" 1 7.5"

Epoxy coated PMMA coated

"PMMA (%) in epoxy/PMMA blend

.� 12 >i " i!! 10 • .a n; "U • .. 8 c-o ...J � 'iii 6 c: � 0 2 4 6 8 1 0 1 2

Tensile load-at-break kgf

14

7.62

9 .86 8 .86 8.80 10. 1 3 9.73 9 .87 9.32 8.39 8.79

16

-

18 20

% PMMA in PMMA I Epoxy Blend

Fig. 1 - Vmiation in tensile load-at-break of PMMAIepoxy blend coated bamboo tibres witl": polymethyl methacrylate content

1 5 .4% respectively. The variation in tensile load-at­break with the percentage of PMMA in the blend is shown in Fig. 1 . It i s clearly evident that the tensile load increases slowly with the increase in PMMA content. However, no regular trend is observed for the increment in tensile load-at-break with PMMA content. The immiscible nature of epoxylPMMA may be responsible for such an observation.

The weight loss/gain for the fibres treated with various chemicals is shown in Table 2. It is observed that the uncoated fibres got completely dissolved in nitric acid after Ih of immersion, whereas the fibres coated with epoxylPMMA blend show weight gain. It is also observed that both the coated and uncoated fibres are resistant to acetic acid, hydrochloric acid, sodium hydroxide, sodium carbonate and ammonium hydroxide. However, it is observed that though the uncoated and epoxy-coated bamboo fibres are resistant to solvents, the blend-coated fibres show a weight loss on solvent treatment. This is due to the fact that PMMA, which is present in the blend, gets dissolved in the solvents. No regular trend in the weight loss/gain is observed for the blend with PMMA. The immiscible nature of the blend may be responsible for such an observation. Further, it is

RAJULU et al.: CHEMICAL RESISTANCE AND TENSILE PROPERTIES OF COATED BAMBOO FIBRES 297

Table 2 - Effect of chemicals on weight of bamboo fibres coated with epoxy, PMMA and their blends

Chemical % change in weight after dipping for 24h Uncoated Epox�/PMMA blend coated fibre Epoxy PMMA

fibre 2.5" 5.0" 7.5"

Acetic acid 1 8.0 6.9 3.3 9.2 Nitric acid Completely 1 0.2 1 3 .8 1 1 .6

dissolved Hydrochloric acid 24.2 1 .7 4.6 5. 1 Sodium hydroxide 1 7.3 1 3. 1 30. 1 0.9 Sodium carbonate 25.6 1 0.3 9.2 1 0.2 Ammonium hydroxide 17.9 6.9 3.8 1 .7 Benzene 1 9.6 -3.4 -5. 1 -0.06 Toluene 22.6 - 1 .5 -4.6 -5.4 Carbon tetrachloride 20.4 -9.0 -9.6 -8.8 Water 27.6 6.4 1 0.7 9.9

"PMMA (%) in epoxy/PMMA blend

observed that the uncoated bamboo fibres absorb high quantity of water (27.6%), while the epoxy-coated fibres are water resistant (water absorption is only 0.7%). The blend coated fibres show intermediate water absorption. Table 2 shows that the blend-coated fibres gain chemical resistance to acids and alkalis whereas the resistance to solvents decreases.

Acknowledgement One of the authors (A VR) is thankful to the

University Grants Commission (UGC), New Delhi, for the award of a major research project.

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