The composite materials are replacing the conventional materials, owing to their excellent properties. The developments of new materials are on the anvil and are thriving day by day. Natural fiber composites such as palm fiber (PF) polymer composites became more enchanting because of their high specific strength, low weight and biodegradability. Mixing of natural fiber like PF with acrylonitrile butadiene styrene (ABS) polymer is finding increased applications. In this work, PF reinforced ABS composites PF-ABS was fabricated by Injection Moulding Machine. The effect of UV-Visible radiation on PF-ABS composites was studied by means of ultraviolet-visible spectroscopy in the wavelength 200 - 1000 nm at room temperature. The present investigation shows that the addition of palm fiber modifies the absorption property of the materials. The absorption ability is maximal for 10% PF-ABS composites while minimal for 20% PF-ABS composites in the visible region of the spectrum. Optical constant like direct band gap energy, Urbach energy and Steepness parameter were determined using absorbance data. The values of direct energy band gap, Urbach energy as well as Steepness parameter were found to be in the range 2.6 - 3.9 eV, 0.40 - 0.85 eV and 0.03 - 0.06, respectively. It was observed that the value of direct band gap energy as well as Urbach energy is higher while the value of Steepness parameter is lower for PF-ABS composites with 10% palm fiber.
Natural fiber (NF) as reinforcing agent in polymer composites has generated much attention in recent years for making low cost engineering materials. Manufacturing industries like automotive, construction and packaging company are searching new materials which can replace conventional non-renewable reinforcing materials such as glass fiber due to pressure of new environmental legislation and consumer demand [
Palm leaves were collected from ten different aged trees from Burura, Comilla, Bangladesh. Hammering was done at the dividing ends of the middle rigid part of the palm leaves. Rigid part of the leaves was kept in underwater for 20 days to rotten. Rotten materials were cleaned and fiber were then separated, dried under sun light and kept at around 100˚C for one day for removal of moisture. ABS polymer was purchased from scientific shop old Dhaka, Bangladesh.
Palm fiber was sliced into 1 - 2 mm in sized. ABS and small palm fiber were dried for 1 day at 50˚C using a dryer. Fined palm fiber and ABS polymer placed into the injection moulding machine. The mixture of palm fiber and ABS polymer was heated at around 150˚C inside the injection molded machine (IMM). The molten mixture became composite and came out of the IMM. This composite was transferred into different shape of die for different test. Composites samples (with 5%, 10% and 20% palm fiber content) were prepared along with pure ABS polymer (0% palm fiber) to accomplish this research.
UV-visible spectroscopy of ABS and composites (containing 1 - 2 mm long fibers as filler) were performed in absorption mode using Shimadzu UV-1601 spectrometer (Shimadzu Corporation, Tokyo, Japan) in the wavelength range 200 to 1000 nm at room temperature. The composite sample which is a rectangular bar was in the dimension of 105.5 mm × 10.5 mm. Before performing test, the samples were kept in the incubator (Memmart, Model: ICP400) at 50˚C for one day, then removed and cooled in the desiccator. The optical absorption was measured with reference to air.
The UV-visible spectroscopy is an important powerful experimental technique for identification of various optical transitions in the materials. The optical energy gaps, the allowed direct and indirect transitions and forbidden transitions of optically active substances can be determined from the UV-visible spectroscopy studied for the potential applications such as light guide materials, optical fibers, optical coating to inhibit corrosion, etc.
The effect of palm fiber loading on the absorbance with respect to wavelength is shown in
In the case of PF-ABS composites, at around 200 nm absorbance was around 2.8 unit (for 10% PF-ABS composites). After 190 nm absorbance decrease up to 400 nm (initial point of visible region). After 400 nm, absorbance of PF-ABS composites exponentially increased up to 700 nm. Absorbance is highest at 700 nm for all PF-ABS composites. This reveals that in the UV region with the decrease of energy (with increase of wave length) absorption decreased which means PF-ABS composites transmit UV-ray rapidly. But in visible region with
the decrease of energy (wave length increased) absorbance increased meaning that low amount of visible light is transmitted. However, after visible region (after 700 nm), with decreasing energy absorption decreases while transmittance increases. The average absorbance of pure ABS and PF-ABS composites with respect to wt (%) of palm fiber in composites is summarized in
Coefficient of absorption (α) is defined as the ability of a material to absorb the light of given wavelength and can be calculated by the Equation (1),
α = 2.303 A t (1)
where A and t are absorption and thickness of the material respectively.
The absorption coefficient at various photon energies for pure ABS and PF-ABS composites is plotted in
Fiber content in composites (%) | Average absorbance |
---|---|
0% | 1.157 |
5% | 2.393 |
10% | 2.552 |
20% | 2.447 |
The optical absorption coefficient was used to determine the band gap energy of the solid polymer composites, using the Tauc relation in the following form [
α h ϑ = R ( h ϑ − E g ) S (2)
where, R is a constant not connected to the energy, Eg the optical energy band gap and S is parameter that describes the nature of band transition. The value of S = 1/2 and 2 correspond to direct and indirect allowed transitions, respectively while that of 3/2 and 3 indicate direct and indirect forbidden transitions, respectively. The Eg can be estimated from extrapolation of the straight-line part of the (αhν)1/S against hν graph to hν = 0. The direct band gap energy (Edg) and indirect band gap (Eig) was computed from the plots (αhν)2 against hν and (αhν)1/2 against hν, respectively which are shown in
obtained values of Edg, are noted in
Generally, the spectral reliance of α is investigated in the region of the photon energies under energy gap of the materials. This region is termed as Urbach spectral tail which indicates the gradient of the exponential edge. The relation between α and photon energy (E) in the Urbach spectral tail region can be expressed as [
α = α 0 exp ( E E u ) (3)
where a 0 , Eu are a constant and Urbach energy respectively. The Eu can be worked out as the tail of the exponential absorption edge or as the breadth of the tails of localized states. The graph obtained by plotting lnα against hν should be linear whose gradient gives the value of Eu. The lnα vs hν plots for pure ABS and PF-ABS composites are represented in
PF-ABS composites (% of palm fiber) | Direct Band Gap (eV) |
---|---|
Pure ABS (0% fiber) | 2.6 |
PF-ABS composites with 5% fiber | 3.5 |
PF-ABS composites with 10% fiber | 3.9 |
PF-ABS composites with 20% fiber | 3.8 |
PF-ABS composites and minimum for pure ABS. The steepness parameter (σ) that represents the expansion of the optical absorption end because of interaction of electron phonon or exciton-phonon [
σ = k T E u (4)
where k and T are Boltzmann constant and absolute temperature, respectively. In calculation of σ in this study, the value of T was 300 K. The calculated values of σ are tabulated in
The value of α as well as λ can be used to find the values of extinction coefficient, K by using the simple equation [
K = α λ 4 π (5)
The variation of K for pure ABS and PF-ABS composites with respect to wavelength of the UV-visible light spectrum is shown in
Wt (%) of palm fiber in composites | Urbach energy, Eu (eV) | Steepness parameter, σ |
---|---|---|
Pure ABS (0% fiber) | 0.40 | 0.06 |
PF-ABS composites with 5% fiber | 0.84 | 0.03 |
PF-ABS composites with 10% fiber | 0.85 | 0.03 |
PF-ABS composites with 20% fiber | 0.61 | 0.05 |
5%, 10% and 20% PF-ABS composite samples, total ten samples from two age groups were taken for extinction co-efficient calculation. The extinction co-efficient of PF-ABS composites is much higher than the pure ABS. The extinction co-efficient increased slightly with the addition of palm fiber in PF-ABS composite. Similar result was found in PVA-LiF composite by S. Hadi et al. [
The UV-visible properties of pure ABS as well as PF-ABS composites were investigated using UV-visible spectrometer. The result indicates that addition of palm fiber modifies absorption property of composite materials. The absorption ability is enhanced for 10% PF-ABS composites. The direct band gap energy varies at 2.6 - 3.9 eV. The highest direct band gap energy is obtained for 10% PF-ABS composites. The values of Urbach energy and Steepness parameter vary at 0.40 - 0.85 eV and 0.03 - 0.06 eV, respectively. Maximum Urbach energy is observed while minimum Steepness parameter is for 10% PF-ABS composites. The extinction coefficient of PF-ABS composites is greater than that of pure ABS polymer matrix.
Neher, B., Bhuiyan, Md.M.R., Kabir, H., Gafur, Md.A. and Ahmed, F. (2018) Fabrication and Optical Characterization of Palm Fiber Reinforced Acrylonitrile Butadiene Styrene Based Composites: Band Gap Studies. Materials Sciences and Applications, 9, 246-257. https://doi.org/10.4236/msa.2018.92016