This research work has been undertaken to fabricate environmentally friendly biocomposites for biomedical and household applications. Sponge-gourd fibers (SGF) obtained from Luffa cylindrica plant were chemically treated separately using 5 and 10 wt% NaOH, acetic anhydride and benzoyl chloride solutions. SGF reinforced polylactic acid (PLA) biocomposites were fabricated using melt compounding technique. Surface morphological, structural, mechanical and thermal properties, as well as antibacterial activities of raw and chemically modified SGF reinforced PLA (SGF-PLA) composites were characterized by field emission scanning electron microscopy, Fourier transform infrared spectrometry, X-ray diffractometry, universal testing method, thermogravimetry, and Kirby-Bauer agar diffusion method, respectively. Surface morphology indicates that after treatment of fibers, the interfacial adhesion between PLA and fibers is improved. X-ray diffractometry result shows that chemical treatment of fibers improves the crystallinity and exhibits new chemical bond formation in the composites. After chemical treatment, compressive strength of the composites is found to increase by 10% - 35%. The thermal stability of the treated fiber reinforced composites is also found to increase significantly. The composites have no antibacterial activities and no cytotoxic effect on non-cancer cell line. Soil burial test has confirmed that the composites are biodegradable. Benzoyl chloride treatment of fibers shows superior mechanical properties and enhances thermal stability among the composites.
Material researchers, engineers and scientists are always determined to produce either improved traditional materials or completely novel materials; composites are an example of the second category. In recent years, the development of biocomposites from biodegradable polymers and natural fibers have attracted great interests in the composite science, because they could allow complete degradation in soil or by composting process and do not emit any toxic or noxious components [
Among biodegradable plastics, polylactic acid (PLA), a linear aliphatic thermoplastic, has been one of the most promising candidates for various applications, because of its agricultural origin and biodegradability [
The primary advantages of using this fiber as additive in polymer are that it has low cost, low density, non-abrasive nature, high possibility of filling levels, low energy consumption, high specific properties, biodegradability, wide varieties, availability throughout the world and a generation of rural/agriculture based economy. The main components of SGF are cellulose and lignin of which the amount of the former one varies from 55% - 90% and the second one is within the range of 10% - 23% [
The effect of chemical treatment, especially alkali and methacrylamide on the mechanical properties of SGF-reinforced polymer composites has been studied earlier [
PLA in pellet form was purchased from Titan chemical, Pasir Gudang, Malaysia. SGF were collected from rural area of Jamalpur district in Bangladesh. The as-received SGF were cut carefully to separate the outer mat core from the inner fiber core. Only the outer mat core was used in this study. Single fibers were separated by hand until fine particulate fibers were obtained. Promising chemical modifiers like sodium hydroxide (NaOH) for alkalization, acetic acid (CH3COOH), acetic anhydride [(CH3CO)2O] and sulphuric acid (H2SO4) for acetylation, and benzoyl chloride (C6H5COCl) and Ethanol (C2H5OH) for benzoylation were procured for treatment of SGF. 1,4-dioxane was purchased from the chemical market in Dhaka for dissolving PLA. All chemical compounds were the products of Merck, Germany.
1) Alkalization
SGF were cut into 10 mm length and were soaked in 5 and 10 wt% solution of NaOH at 30˚C maintaining a liquor ratio of 20:1. The fibers were washed with distilled water to remove dirt and other water soluble impurities and then immersed in NaOH solution for 2 h. They were washed several times with fresh water to remove NaOH solution sticking to the fiber surface, neutralized with dilute acetic acid solution and finally washed again with distilled water to maintain the pH value of 7. The fibers were sonicated for 1 h at 50˚C in an ultrasonic cleaner [model: VGT-1860QTD, MTI, USA] and then dried at room temperature for 48 h followed by oven drying at 100˚C for 6 h.
2) Acetylation
10 g dried SGF were immersed in distilled water for 15 min, pressed out and then introduced in a Buchner funnel. The wet fibers were transferred to a stoppered bottle and covered with 150 ml of glacial acetic acid. After being shaken occasionally for 1 h, the fibers were pressed out as before. Then a solution of 10% acetic acid in distilled water and 1 ml concentrated H2SO4 at 25˚C was prepared. The SGF were kept in this solution. The mixture was shaken vigorously for about 1 min and then 50 ml of 5 and 10 wt% acetic anhydride solution was added and again shaken vigorously for about 1 min. The resultant solution was held 5 min at 25˚C. The SGF were sonicated for 1 h at 50˚C in an ultrasonic cleaner. The SGF were then washed with distilled water. Finally, the fibers were dried at 60˚C and then stored in desiccators.
3) Benzoylation
The SGF were initially alkaline pre-treated in order to activate the hydroxyl groups of the cellulose and lignin in the fibers. Then the fibers were suspended in 10% NaOH, and 5 and 10 wt% solution of benzoyl chloride for 15 min. The isolated fibers were then soaked in ethanol for 1 h to remove the benzoyl chloride. Then the fibers were sonicated for 1 h at 50˚C in an ultrasonic cleaner. Finally, the fibers were washed with distilled water and dried in an oven at 80˚C for 24 h.
1) Preparation of neat PLA foam
In a beaker, neat PLA was dissolved in 1,4-dioxane by stirring with a magnetic stirrer and heating simultaneously. After 20 - 30 minutes the solvent is turned into viscous form. The viscous material was placed in a square shaped pot. After cooled in normal temperature the pot was placed in a refrigerator at −20˚C. After 24 h the sample was shifted to the vacuum dryer. After 24 h the sample was removed from the dryer and obtained as foam. The prepared neat PLA foam is here-in-after abbreviated as PLAF.
2) Composite preparation
The composites were prepared by solution mixing with SGF and PLA pellets dissolved in 1,4-dioxane by stirring using a magnetic stirrer and heating simultaneously. The prepared composites are coded as untreated fiber reinforced PLA composites (UFPC), alkali treated fiber reinforced PLA composites (ALT-FPC), acetic-anhydride treated fiber reinforced PLA composites (ACT-FPC) and benzoyl-chloride treated fiber reinforced PLA composites (BCT-FPC). The composites, prepared with fibers treated at 5 wt% chemical concentrations are here-in-after indicated as 5ALT-FPC, 5ACT-FPC and 5BCT-FPC, and that prepared with fibers treated at 10 wt% chemical concentrations are here-in-after indicated as 10ALT-FPC, 10ACT-FPC and 10BCT-FPC. 5 and 10 wt% chemically modified fiber reinforced composites are here-in-after introduced as 5TFPCs and 10TFPCs, respectively. In all of these composites the fiber content is 5 wt%.
Water intakes of the composites were measured according to ASTM: C-67-91. The test specimens were cut in a size of 6 cm length, 2 cm width and 0.5 cm thickness. The cut samples were kept in an oven at 80˚C for 24 h. It was taken out from the oven and immediately weighed. Let this weight be Wi. The samples were then immersed in distilled water of 23˚C and kept for 24 h. It was taken out from the water, wiped by a cloth, dried in air and then weighed. Let this weight be Wf. Then the amount of water intake was calculated by the following formula:
Water intake (%) = [ W f − W i W f ] × 100 (1)
The above procedures were repeated for 2 days to 30 days for all samples. It is noteworthy that the cut sides of the samples were coated with araldite to prevent from penetrating water into the sample.
The degradation under soil of the composites was performed according to ASTM: G-160. For this method, the samples were kept in an oven at 80˚C for 24 h. It was taken out from the oven and immediately weighed. Let this weight be wi. The samples were then buried under soil kept in a pot. The pot was covered with a plastic net and exposed to atmospheric conditions for 7 days. Readings were taken of the changes in the weight loss of the samples at intervals of 7 days for approximately one month. To determine the weight loss the specimen of each sample was taken out from the soil, wiped by a dry cloth or tissue paper, quickly washed with cold water and dried in an oven at 80˚C to a constant weight. Let this weight be wf. Then the percentage of weight loss was calculated by the following formula:
Weight loss (%) = [ w i − w f w i ] × 100 (2)
Fourier Transform Infrared (FTIR) spectra of the samples were recorded at room temperature by using a double beam IR spectrophotometer (model: Frontier, FT-IR/NIR Spectrometer, PerkinElmer, Japan) in the wave number range of 650 - 4000 cm−1. For these measurements, the samples were crushed for recording the attenuated total reflectance (ATR)-FTIR spectra in the transmittance (%) mode.
The Bruker D8 ADVANCE XRD was used for taking pattern of X-ray diffraction (XRD). In this machine, a high voltage power supply (35 kV, 20 mA) was used to generate X-ray radiation. The composites were finely ground to prepare the disc specimen of same thickness for each category of samples. 1 g chopped samples were compressed in a cylindrical mold with a pressure of 1 MPa. The samples were step-wise scanned by XRD over the operational range of scattering angle between 10˚ to 30˚, with a step of 0.02˚, using the CuKα radiation of wavelength λ = 1.5406 Å. The data were recorded in terms of the diffracted X-ray intensity (I) versus 2θ. The relative intensity is calculated by the following equation:
I = I T F P C I U F P C (3)
Compressive strength (CS) tests of PLAF, UFPC and differently treated fiber reinforced PLA composites (TFPCs) were performed by a universal testing machine (UTM) (model: H10KS, Hounsfield, UK) following ASTM: D-638-98 at a crosshead speed of 1 mm/min, keeping a gauge length of 10 mm. The CS values were calculated by the following equation:
Compressive strength, CS = P/A (4)
where P = Maximum load applied to the sample, A = Area of the sample (for the four-sided specimen, A = LW, where L is the length and W is the width of the sample).
The fractured samples of PLAF, UFPC and TFPCs obtained from the compressive strength tests were examined using a field emission scanning electron microscope (FESEM) (model: JSM-7600F, Jeol, Japan) at an acceleration potential of 20 kV. The fractured surfaces of the specimens were sputter-coated with a thin layer of platinum using a JFC-1600 auto fine coater.
Thermo gravimetric analyzer (TGA) coupled with a differential thermal analyzer (DTA) (model: EXSTAR, TG/DTA 6300, Seiko, Japan) was used in this study. The samples were heated from room temperature up to 600˚C in a nitrogen atmosphere at a heating rate of 20˚C/min. TGA is used primarily for determining thermal stability of samples. Data are recorded as thermograms of weight versus temperature.
Antibacterial activities of UFPC, ALT-FPC, ACT-FPC and BCT-FPC were measured against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus with agar diffusion method by Kirby-Bauer, 1985 [
Cytotoxic effect of the samples was also examined. Vero cell line, kidney epithelial cells extracted from an African green monkey, was maintained in Dulbecco’s modified eagles’ medium (DMEM) containing 1% penicillin-streptomycin (1:1) and 0.2% gentamycin and 10% fetal bovine serum (FBS). Cells (3.7 × 104/250 µl) were seeded onto 48-well plates and incubated at 37˚C + 5% CO2. Next day, autoclaved samples were added to each well. Cytotoxicity was examined under an inverted light microscope after 72 h of incubation. Duplicate wells were used for each sample.
The degradation of composites has been evaluated by measuring the weight loss of samples, which have been soil buried in outdoor for 28 days.
The ATR-FTIR spectra of the PLAF, UFPC, ALT-FPC, ACT-FPC and BCT-FPC are shown in
variation in the FTIR spectra of
From the above stated experiment of FTIR, especially from
The XRD patterns of PLAF, UFPC, ALT-FPC, ACT-FPC and BCT-FPC are illustrated in
The compressive strength (CS) test results for PLAF, UFPC, and 5 and 10TFPCs are shown in
In all of the composites, the CS value is found to increase by 10% - 35% after chemical treatment. This increase can be attributed to the reduction in the
porosity of foam type PLA and an enhancement in mechanical bond strength [
the interfacial adhesion between matrix and SGF powder is found to be improved. In
temperature at 50% weight loss is considered as the thermally stable temperature for the sample [
Sample | To ˚C | Ts ˚C | Te ˚C |
---|---|---|---|
PLAF | 315.58 | 349.80 | 370.74 |
UFPC | 286.33 | 322.71 | 338.87 |
5ALT-FPC | 323.77 | 356.72 | 380.02 |
10ALT-FPC | 326.40 | 356.85 | 382.06 |
5ACT-FPC | 303.93 | 353.93 | 379.04 |
10ACT-FPC | 324.22 | 357.00 | 386.58 |
5BCT-FPC | 331.85 | 363.85 | 386.92 |
10BCT-FPC | 368.82 | 405.34 | 423.69 |
From the results presented in
peak of DTA for all samples indicate the melting temperature (Tm) of the samples. The starting points of second endothermic peak correspond to the degradation temperatures (Td) of the samples. The DTA indicates that the Tm value of 5ALT-FPC is more than others, but the Td value of 10BCT-FPC is 404.41˚C, which appears as the highest value observed among the composites. The Tm and Td values for different samples are inserted in
The observed results strongly suggest that the benzoyl chloride treated fiber reinforced PLA composites are thermally more stable than others and the chemical treatments of SGF result in slow thermal decomposition. This may be connected to the different decomposition behaviors of the molecules of the differently treated SGF. The decomposition of the parent molecule, benzoyl chloride, is highly condition-dependent with the sample heating rate and temperature of decomposition playing a preponderant role in the course of the decomposition [
Sample | Tm ˚C | Td ˚C |
---|---|---|
PLAF | 173.43 | 385.38 |
UFPC | 173.00 | 319.00 |
5ALT-FPC | 195.85 | 384.00 |
10ALT-FPC | 182.88 | 385.50 |
5ACT-FPC | 184.70 | 363.74 |
10ACT-FPC | 189.42 | 387.20 |
5BCT-FPC | 180.00 | 391.80 |
10BCT-FPC | 192.69 | 404.41 |
The protocols in this research describe the growth and maintenance of Vero cells using DMEM as the culture medium. The DMEM is a very common culture medium, but a variety of other media can also be successfully used with Vero cells. Depending on the application, it may be desired or necessary to count the number of cells (i.e., if a specific number of cells need to be analyzed, plated, etc.). The concentration of cells in suspension (following trypsin treatment) was determined using a hemacytometer. In this Figure, the black shadows indicated the amount of death cells and the light colors indicated the survivor cells. The images proof that the prepared samples are not harmful for non-cancer cell of human body.
The chemical modifications of SGF have accelerated the degradation under soil of the SGF-PLA composites, showing increased percentage of weight loss. The additional peak found for ACT-FPC and BCT-FPC from the FTIR analysis demonstrates that the acetic anhydride and benzoyl chloride have interacted chemically with the SGF. The increased intensity of the XRD peak suggests an
Sample ID | Survival of cells (Vero) | Remarks/Results |
---|---|---|
Solvent (-) | 100% | No cytotoxicity was observed on Vero cell (non-cancer cell) line. |
5 ALT-FPC | >95% | |
5 ACT-FPC | >95% | |
5 BCT-FPC | >95% |
increase in crystallinity of the composites. The formation of voids within the PLA matrix is minimized by fiber treatment, indicating that after the treatment of SGF with chemicals, the interfacial adhesion between PLA and SGF is improved. The chemical treatment of SGF has increased the compressive strength of the composites. The highest value of mechanical strength and thermal stability are found for BCT-FPC. The composites show no antibacterial activities, confirming degradable by bacteria or other micro organs in environment. The composites also didn’t show any cytotoxicity on Vero cell (non-cancer cell) line, so that non-cancer cell will be grown and these are not harmful to use in human body for medical purposes. The composites, prepared by treated SGF can be used by substitute of the non-degradable composite materials.
Al-Mobarak, T., Gafur, Md.A. and Mina, Md.F. (2018) Preparation and Characterization of Raw and Chemically Modified Sponge-Gourd Fiber Reinforced Polylactic Acid Biocomposites. Materials Sciences and Applications, 9, 281-304. https://doi.org/10.4236/msa.2018.92019