Preparation of Raw Jute Fabric Reinforced and Low Lignin Content Modified Jute Fabric Reinforced Polyester Composites-Effects of Gamma Radiation on Their Properties
Md. Asadul Hoquea*, Md. Anwarul Kabir Bhuiyaa, Md.
Saiduzzamana , Md. Ashadul Islama
aDepartment of Materials Science & Engineering, University of Rajshahi,
Rajshahi-6205, Bangladesh.
*E-mail: [email protected]
Mubarak A. Khanb and S. M. Shauddinb
bInstitute of Radiation and Polymer Technology, Bangladesh Atomic Energy Commission,
Dhaka-1000, Bangladesh.
Abstract—Raw jute fabrics reinforced polyester composite (as RJPC) and polyethylene glycol modified bleached jute fabrics reinforced polyester composite (as MBJPC) were fabricated by the heat-press molding technique. Prior to the composite formulation, low lignin content bleached jute fabrics were chemically modified with polyethylene glycol for the better compatibility of the fabrics with the polyester matrix and enhancing elongation properties. All the composites were heat cured and thereafter irradiated with γ-ray at various doses for the complete cross-linking of the matrix phase. The irradiated composites showed highest improved physical and mechanical properties at the 1000 Krad γ-radiation dose. However, the hard and sunlight sensitive high lignin content raw jute fabrics reinforced polyester composites (γ-RJPC) showed higher tensile strength, tensile modulus, flexural strength and flexural modulus compared to that of low lignin content irradiated modified bleached jute fabrics reinforced polyester composite (γ-MBJPC).
On the contrary, γ-MBJPC showed higher elongation properties than that of γ-RJPC. After the γ-ray irradiation, both the γ- RJPC and γ-MBJPC developed high degree of cross linking among the polyester molecules and thereto fabrics with the consequence of significant changed of surface morphology as observed by AFM, which ultimately lead to improved mechanical properties.
Key words: Raw jute fabrics, Modified jute fabrics, Polyethylene glycol, Polyester resin, γ-radiation, Composites, Mechanical properties
I. INTRODUCTION
The advancement in the field of material science led to many new and advanced materials. Composites are one of them, which are adopted in various engineering applications.
Many authors [1–3] stated many properties of natural fibers reinforced plastics which make them suitable for a variety of applications. The use of natural fibers as reinforcements in polymer composites to replace synthetic fibers like glass and carbon is currently receiving increasing attention because of
the advantages, including cost effectiveness, low density, high specific strength, biodegradability as well as their availability as renewable resources [4]. Currently, a wide variety of agricultural species like straw, jute, bamboo, sisal or pineapple leaf, have been considered for use in the production of plant fibre reinforced polyester composites [5–7]. Many authors have reported a number of natural fibre reinforced polymer composites showing the dependency of physical and mechanical properties on the nature, mass fraction and orientation of the fibres in the matrix phases and, molding temperatures and pressures [8-10].
Jute, a lingo-cellulosic fibre crop of international eminence and a large volume of agricultural product of Bangladesh, possess good mechanical properties at low density, which makes them fit as reinforcements in the preparation of natural fiber reinforced polymer composites. The incorporation of jute or jute fabrics in the composite materials will create a new frontier for proper utilization of this large volume agricultural product of Bangladesh. But the main objection of using jute in transparent composites is the photo-degradation of the jute which causes the abrupt fall of tensile strength of the composites. This photo-degradation occurs due to the presence of high percentage of UV sensitive lignin that acts as the cementing materials for the bridging of fibre units. This high lignin content can be reduced by controlled bleaching of jute fibres or fabrics with minimum loss in mechanical properties. However, recently, many authors have reported that chemically modification of jute could improve its physical and mechanical properties as well as reduces light sensitivity [11-12].
We, here mainly emphasize the use of low lignin content chemically modified bleached jute fabrics as the long lasting reinforcement component in the polymer matrix composite and a comparative study is made on the physical and mechanical properties of low lignin content modified jute composite and raw jute composite.
II. EXPERIMENTAL
Materials
Jute fabrics (Tossa jute) were collected from the local market of Rajshahi, Bangladesh. Polyester resin and methyl ethyl ketone peroxide were procured from Luxchem Polymer Industries, Malaysia and Beijing Credit New Material Co., respectively. Hydrogen peroxide, polyethylene glycol (PEG), and aluminium sulphate, sodium silicate, sodium triphosphate, sodium carbonate were purchased from Merck (India).
Methods and Instrumentations
Scouring: Scouring of jute fabric was performed using a solution containing 2 gm/L of sodium carbonate and 1 gm/L of a nonionic detergent at a fabric-to-liquor ratio of 1:20 (W/V) at 60°C for 30 min, where after, the fabric was washed with water and dried in air [13].
Bleaching: Bleaching of the jute fabric was performed in aqueous media using a solution containing 0.5% hydrogen peroxide (H2O2), 1.66% sodium silicate, 0.42% trisodium phosphate (Na3PO4), 0.08% sodium hydroxide and 0.08%
nonionic detergent in a 1000 mL beaker at a fabric-to-liquor ratio of 1:6 (W/V) for 1 h at 80°C. After bleaching, the fabric was washed with distilled water, neutralized with dilute acetic acid and finally washed with distilled water until the wash liquor was neutral.
Surface Modification: Bleached jute fabrics were treated with optimum condition of 100% PEG and 6% Al2(SO4)3 for 90 minutes at 70°C temperature for the grafting of PEG onto the jute surfaces. Prior to the modification, optimum PEG conc., Al2(SO4)3 conc. time and temperature were determined.
IR Spectroscopy: FT-IR spectroscopic measurements were carried out with Spectrum-100, FT-IR Spectrum, Perkin Elmer using KBr pellet technique. The jute fabric samples were cut into very small pieces. Then, the measurements were performed by mixing and grinding a small amount of samples (1 mg) with dry and pure KBr (200 mg). Mixing and grinding were accomplished in a mortar by a pestle [14].
Composite Fabrication: The jute fabrics (raw jute fabrics or modified bleached jute fabrics) were sandwiched with unsaturated polyester resin containing methyl ethyl ketone peroxide (MEKP) as cross-linking agent. The resin and cross- linking agent were mixed in the ratio of 1:0.02 by weight.
Composite sheets of desired size (15cm ×13cm) were prepared by compressing three layers of jute fabrics in between the liquid polyester resin mixed with cross-linking agent. The prepared sandwich was then compressed in the
heat press (Carver, INC, USA, model 3856) at 105oC for 5 min under 5 tons pressure.
Irradiation: The composite samples made with raw jute fabrics and modified bleached jute fabrics were irradiated using a Co-60 gamma source (25 kci) with the different doses of 200-1400 Krad at Bangladesh Atomic Energy Commission, Savar, Dhaka, Bangladesh.
Mechanical Testing: The tensile and bending tests of the composites were carried out by a universal testing machine (Hounsfield H50KS) according to ASTM D638 and ASTM D790 standard methods, respectively. All the results were taken as the average value of five samples.
Atomic Force Microscopy (AFM): Study of atomic force microscopy (AFM) was carried out with “XE70 Park Systems” in contact mode system. Samples viewed by AFM do not require any special treatments (such as metal/carbon coatings) and does not typically suffer from charging artifacts in the final image.
III. RESULTS AND DISCUSSION
Modification of Jute Fabric
Modification of bleached jute fabric with PEG was performed with the optimized monomer conc. (100%), catalyst conc. (6%), modification time (90 min) and temperature (70°C). From the Fig. 1 it is seen that beyond the optimum conditions, grafting of PEG started to decreased, and this is due to the increasing rate of homopolymerization rather than grafting at the higher monomer and catalyst concentration, longer reaction time and elevated temperature of modifying bath [14,15].
IR Spectra of bleached and modified jute fabric
The infrared spectra of the bleached (a) and PEG treated bleached jute fabrics (b) are presented in Fig. 2. Bleached jute fabric contains hydroxyl group (–OH) as well as carboxylic
Fig. 1 Modification of jute fabric with PEG at optimum conditions.
group (–COOH) which gave overlapping IR absorption in the wide range of 3600–2500 cm-1. While the modification of bleached jute with PEG, the number of hydroxyl group increased and decreased in carboxylic groups which is predicted as the narrowing of overlapping absorption of –OH and –COOH in the IR spectra of modified jute fabric. The intense hydroxyl absorption is attributed as the hindrance of hydrogen bonding of –OH groups attached to the bulky cellulosic ring structures. The –C–H stretching in the bleached jute is seen in around 2920–2850 cm-1 (–C–H of cellulosic structure) which in the modified fabric becomes as intense absorption (of –C–H of cellulosic unite and PEG) confirming the attachment of PEG by modification.
Tensile Strength (TS) and Flexural Strength (FS)
Tensile strength (TS) and Flexural strength (FS) of raw jute fabric reinforced polyester composites (RJPC) and modified bleached jute fabric polyester composites (MBJPC) with and without γ-radiation have been shown in Fig. 3. It is observed that, both the TS and FS of the RJPC showed higher values than that of MBJPC with and without γ-radiation. This may be explained in terms of higher lignin content that is responsible for the higher stiffness of the raw jute fabric that imparts higher tensile strength and tensile modulus in RJPC.
Again, the increased values of tensile strength and tensile modulus for the RJPC and MBJPC after γ-radiations are due to the increase in cross-linking in the polyester matrix.
Although raw jute fabric reinforced polyester composites shows superior properties of TS and FS, prolong exposure to sunlight will cause rapid deterioration of the properties by the photochemical degradation of lignin in raw jute fabric [16].
Tensile Modulus (TM) and Flexural Modulus (FM)
It is seen from the Fig. 4 that Tensile Modulus (TM) and Flexural Modulus (FM) of raw jute fabric reinforced polyester composite (RJPC) are higher than that of modified bleached jute fabric reinforced polyester composite (MBJPC). As higher the values of TS and FS indicate more stiffness and low flexibility, MBJPC will be more flexible and will show higher elongation of breaking. Inherently the low lignin content of modified jute fabric shows more flexibility and higher elongation than that of raw jute fabric, so modified bleached jute fabric originates higher flexibility in MBJPC.
Again, TM and FM of both the composites increased after γ-radiation with persisting higher values for raw jute fabric reinforced composites are attributed as the increased in cross- linking extend in the matrix.
Elongation at break
Elongations at breaking of raw jute fabric polyester composite and modified bleached jute fabric polyester composite were measured before and after γ-irradiations. The
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400 225
%, Transmitance(a.u)
Wavenumbers (cm-1) C – H Streching
2905.78 – OH
– OH a nd –COOH Overla pping
– CO – – CO – (a)
(b)
Fig. 2 IR Spectra of bleached jute fabric (a) and modified jute fabric (b)
0 30 60 90 120 150
RJPC γ-RJPC MBJPC γ-MBJPC Mechanical Strength (MPa)
Sample Name
TS FS
Fig. 3 Tensile Strength (TS) and Flexural Strength (FS) of raw and modified jute reinforced composites at 27 wt% jute content before and after γ- radiation (1000 Krad).
0 1 2 3 4 5
RJPC γ-RJPC MBJPC γ-MBJPC Mechanical Strength (GPa)
Sample Name
TM FM
Fig. 4 Tensile Modulus (TM) and Flexural Modulus (FM) of raw and modified jute reinforced composites at 27 wt% jute content before and after γ-radiation (1000 Krad).
elongation properties are shown in the Fig. 5. From the figure, it is seen that the higher elongations were observed for the composites before irradiation and maximum elongation of breaking (7.23%) was found for the composite prepared with modified bleached jute fabric. This is because of the flexible nature of low lignin content of bleached jute, which further became more flexible by the chemical modification with polyethylene glycol (PEG). Furthermore, PEG acts as the flexible bridging component between the fabric and matrix provide the additional elongation for MBJPC compared to RJPC. The lower flexibility of composites after radiation may be attributed as the increased of cross-linking in the matrix by irradiation which made the composites more ductile.
Surface morphology analysis
By using AFM, the surface of raw jute fabric and modified jute fabric reinforced polyester composites (RJPC and MBJPC) were observed before and after γ-irradiations. The AFM images of the composites surfaces are shown in Fig. 6 where the surfaces of the composites (RJPC and MBJPC) without irradiation [Fig. 6 (a) and (c)] showed smoother than the composites with irradiations. Radiation induces highly dense cross-linking in the matrix which improve the compactness and increase the roughness of the surfaces as can be seen in the [Fig. 6 (b) and (d)].
IV. CONCLUSION
Raw jute fabric reinforced polyester composite (γ-RJPC) showed better tensile strength, tensile modulus, flexural strength and flexural modulus compared to that of PEG treated bleached jute fabric reinforced polyester composite (γ- MBJPC) for both the γ-irradiated or non-irradiated composites. However, as the lignin undergoes rapid photochemical degradation, rapid loss in tensile strength will be occurred for raw jute fabric reinforced polyester composite than PEG treated bleached jute fabric reinforced polyester composite. Due to the elastic bridging of PEG in between fabric and polyester matrix, PEG modified bleached jute fabric reinforced polyester composite showed better elongation at breaking for the composites with or without radiation compared to that of raw jute fabric reinforced polyester composite. As the physical and mechanical properties of both the raw jute and modified bleached jute fabric reinforced composites are comparable, γ-MBJPC will perform better for the long range applications.
ACKNOWLEDGEMENT
The authors are very much grateful to National Science &
Technology (NST), Bangladesh for their financial support and also grateful to Atomic Energy Commission (AEC), Bangladesh for giving support for laboratory facilities.
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