The evaluation of bean pod ash particles on the properties of recycled low density polyethylene (RLDPE) composites was studied. The RLDPE/bean pod ash particles (CBPp) composites were produced using compounding and compressive moulding techniques. Factorial design of experiment and analysis of variance (ANOVA) were employed for optimization. The mechanical properties and microstructure of the composites were determined. The results obtained showed that the optimum values of flexural strength were obtained at 140°C, 12 minutes, 40 wt% CBPp and 6 Mpa. The hardness values, tensile and bending strengths of the composite increased by the addition of beans pod ash particles to RLDPE composites. Compressive properties of RLDPE matrix and composites were 13.00 and 18.25 N/mm2. The fairly uniform distribution of the bean pod ash particles in the microstructure of the composites is the major factor responsible for the improvement in the mechanical properties. The obtained results of the developed composites have shown that the beans pod waste could be used as a biodegradable eco-friendly reinforcement.
In recent years there is a perceived shortage of wood fibre for composite products due to competition for fibre by pulp mills, reduced harvest and diminished log quality. Also, there is pressure from environmentalists to reduce forest use and regulatory legislation pending on disposal of agro-fibres [
During the past few decades, many polymer composites have been prepared and combined with various types of synthetic reinforcing fillers in order to improve the mechanical properties and obtain the characteristics demanded in actual applications [
There are lots of waste materials from beans pod and water sachets (recycled low density polyethylene) found in Nigerian environment. These constitute nuisance to the environment. Our desire in this study is to produce and evaluate the mechanical properties of recycled low density polyethylene/bean pod ash particulate bio- composites.
Factorial design and linear regression techniques have been widely used in the engineering analysis. These techniques consist of plan of experiments with objective of acquiring data in a controlled way, executing these experiments in order to obtain information about the behaviour of a given process [
where: A = temperature, B = time, C = reinforcer/polymer content, D = pressure.
The model selected includes the effects of main variables first-order and second-order interactions of all variables. Hence the general model is written as:
were b0 is average response of Y and b1, b2, b3, b4, b5, b6, b7, b8 are coefficients associated with each variable A, B, C, D and interaction.
Variables | Actual value | Coded value | ||
---|---|---|---|---|
Low level | High value | Low level | High value | |
Temperatures(˚C), A | 140 | 160 | −1 | +1 |
Time(minutes), B | 6 | 12 | −1 | +1 |
Reinforcer/polymer (wt%), C | 40/60 | 60/40 | −1 | +1 |
Pressure (Mpa), D | 3 | 6 | −1 | +1 |
S/No. | Temperature (˚C) | Time (minutes) | Reinforcer/polymer (wt%) | Pressure (Mpa) |
---|---|---|---|---|
S1 | 140 | 12 | 40/60 | 6 |
S2 | 160 | 12 | 40/60 | 3 |
S3 | 160 | 12 | 60/40 | 6 |
S4 | 160 | 6 | 40/60 | 6 |
S5 | 140 | 6 | 40/60 | 3 |
S6 | 160 | 6 | 60/40 | 3 |
S7 | 140 | 12 | 60/40 | 3 |
S8 | 140 | 6 | 60/40 | 6 |
Flexural strength was used as performance characteristics to deduce the optimal manufacturing parameters by using the fractional design and analysis of variance (ANOVA). The response data was analyzed using analysis of variance (ANOVA) technique at 0.05 levels of significance. Finally, degree of contribution of each signifi- cant factor was obtained so as to determine the level of its statistical importance in the model. The percentage (%) contribution gives idea about the degree of contribution of the factors to the measured response [
The uncrushed beans pods were cleaned with water and dried. After drying, the beans pods were packed in a graphite crucible and fired in a control atmosphere muffle electric furnace at a temperature of 1200˚C for 5 hours to form carbonized beans pod particles. The particle size analysis of the beans pod particles was carried out in accordance with ASTM-60. 100 g of the beans pod particles was placed into a set of sieves arranged in descending order of fineness and shaken for 15 minutes which is the recommended time to achieve complete classification. The weight retained on 100 µm was used in this research [
The RLDPE matrix and the bean pod particles were pre-dried prior to the compounding. The mixture was compounded using co-rotating twin extruder (APV Baker Ltd. England, Model: MP19PC) with L/D ratio of the screw of 25:1. Mixing speed of 60 rpm was maintained for all the compositions [
The microstructure of the bean pod particles and surface morphology of the composites were studied using a JOEL JSM 5900LV Scanning Electron Microscope equipped with an Oxford INCATM Energy Dispersive Spectroscopy system. The samples were firmly held on the sample holder using a double-sided carbon tape before putting them inside the sample chamber. The SEM was operated at an accelerating voltage of 20 Kv. The digitized images were recorded.
Before the test the samples were cut from the composites for the mechanical test in according with the recommended Standard. Prior to the test, all the samples were conditioned at a temperature of 23˚C ± 2˚C and relative humidity of 65% according to ATM D618-08 [
The flexural test was used for the optimization analysis. Flexural tests were performed on housefield tensometer testing machine. A three point bending configuration was used with specimen nominal dimension of 150 × 50 × 4 mm and a span of 96 mm. The load was applied continuously throughout the test at a uniform rate 3 mm/min [
The XRF chemical composition of the carbonized beans pod ash particles is represented in
The XRD pattern of the bean pod ash particles revealed that, the major diffraction peaks are 44.05˚, 36.06˚, 45.12˚, 47.21˚ and 26.12˚ and their inter-planar distance are 2.38 Å, 2.25 Å, 3.31 Å and 2.62 Å. Their relative intensity of X-ray scattering are 10.02, 11.79, 44.31, 1.36 and 100.00 and phases at these peaks are Carbon (C), Quartz syn (SiO2), Iron Silicon (Fe 1.34 Si 0.66), Iron Carbide (Fe7C3) and Moissanite (SiC) respectively (
Morphology of the bean pod ash particles by SEM/EDS is showed in
Oxide | SiO2 | Al2O3 | Fe2O3 | CaO | MgO | Na2O | K2O | L OI |
---|---|---|---|---|---|---|---|---|
wt% | 80.24 | 0.5 | 15.67 | 3.0 | 0.6 | 0.24 | 0.32 | 9.5 |
For the optimization of the flexural strength, the upper level and the lower level of each variable along with their coded values used in this investigation are shown in
The model equation was obtained after calculating each of the coefficients of Equation (2) using
From Equation (3) it was observed that the coefficient of A (temperatures) is negative, that of B (time) is positive, that of C (reinforce/polymer) is negative and the interaction between AC is also negative. These mean that by increasing the temperature from 140˚C to 160˚C, the flexural strength decreased by −1.02. Again, by increasing the time from 6 to 10 minutes increased the flexural strength by 0.65, while by increasing the reinforcer from 40 to 60 wt% also decreased the flexural strength by −0.88 and by increasing the temperatures and reinforcer at the same time decreased the flexural strength by −0.17. These explanations can be seen clearly in
Substituting the coded values of the variables for any experimental condition in Equation (3), the flexural strength for the composites can be calculated.
It is evident from
S/n | x0 | A | B | C | D | AB | AC | AD | F |
---|---|---|---|---|---|---|---|---|---|
1 | 1 | 1 | −1 | 1 | −1 | −1 | 1 | −1 | 5.70 |
2 | 1 | 1 | −1 | −1 | 1 | −1 | −1 | 1 | 5.67 |
3 | 1 | 1 | 1 | −1 | −1 | 1 | −1 | −1 | 6.79 |
4 | 1 | −1 | 1 | 1 | −1 | −1 | −1 | 1 | 7.50 |
5 | 1 | −1 | −1 | −1 | −1 | 1 | 1 | 1 | 7.34 |
6 | 1 | −1 | −1 | 1 | 1 | 1 | −1 | −1 | 5.5 |
7 | 1 | −1 | 1 | −1 | 1 | −1 | 1 | −1 | 8.50 |
8 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 5.67 |
ANOVA was used to determine the design parameters significantly influencing the flexural strength. The values of F calculated (F = Fishers distribution) were compared with F critical. F distribution critical values for degrees of freedom (1, 7) at 95% confidence level (see
The optimum values of flexural strength was predicted at the selected levels of significant parameters and their optimum levels have already been selected as A (140˚C), B (12 minutes), C (40 wt% CBPp) and D (6 Mpa) for the composites (see
SEM was used to study the morphology of RLDPE/bean pod ash particles composites.
Flexural strength for composites | ||||||
---|---|---|---|---|---|---|
Source | Sum of squares | DF | Mean square | Fvalue | Pvalue | Remarks |
Model | 18.13 | 4 | 4.53 | 38.32 | 0.0066 | Significant |
A | 8.30 | 1 | 8.30 | 70.18 | 0.0036 | Significant |
B | 3.34 | 1 | 3.34 | 28.24 | 0.0130 | Significant |
C | 6.25 | 1 | 6.25 | 52.81 | 0.0054 | Significant |
AB | 1.10 | 1 | 1.10 | 26.34 | 0.0559 | Not significant |
AC | 0.24 | 1 | 0.24 | 2.04 | 0.2484 | Not significant |
AD | 1.95 | 1 | 1.95 | 46.59 | 0.0508 | Not significant |
Residual | 0.35 | 3 | 0.12 | |||
CorTotal | 18.49 | 7 |
Process parameter | Parameter designation | Optimal level |
---|---|---|
CBPp | ||
Temperature (˚C) | A | 140 |
Time (minuets) | B | 12 |
Bean pod particles/polythene content (wt%) | C | 40/60 |
Pressure (Mpa) | D | 3 |
Conditions | Tensile strength (N/mm2) | Compression strength (N/mm2) | Bending strength (N/mm2) | Impact Energy(J) | Hardness values HRB |
---|---|---|---|---|---|
RLDPE matrix | 3.90 | 13.00 | 7.10 | 4.30 | 2.81 |
CBPp composites | 6.25 | 18.25 | 4.51 | 2.65 | 10.67 |
composites. Particles-matrix interface plays an important role in composite properties. A strong particles-matrix interface bond is critical for high mechanical properties of composites.
The hardness of the composite reinforced with CBPp was greater than that of unreinforced and this is because the CBPp filler contains more carbon, has smaller particles and has given off all combined moisture resulting to an increase in the hardness of the composite. However the composites have higher hardness values than the matrix. For example the hardness values of 2.81 HRB and 10.67 HRB (see
The tensile strength of the composites decreased slightly as the beans pod ash particles loading increased beyond 40 wt%. It clearly indicates that addition of beans pod ash particles improve the load bearing capacity of the composites. Similar observations have been reported by Agunsoye et al. [
Nevertheless the tensile strength obtained in this study remained within acceptable levels for outdoor and indoor structural applications [
Compressive properties of RLDPE matrix and composites are 13.00 and 18.25 N/mm2 respectively (see
The impact strength decreases with increasing bean pod ash particles in the RLDPE matrix. This is mainly due to the reduction of elasticity of material due to filler addition and thereby reducing the deformability of matrix. An increase in concentration of filler reduces the ability of matrix to absorb energy and thereby reducing the toughness, so impact strength decreases. Also it is obvious that plastic deformation of the mixed polymer matrix and the non-deformable reinforcement is more difficult than the polymer matrix. These results are in agreement with the work of other researchers [
The tensile properties are in agreement with the results obtained from the analysis of the hardness and impact strength. The increase in hardness is related with high tensile modulus and the increasing amount of hard bean pod ash particles in the RLDPE matrix. On the other hand, as can be suggested from the impact test, the elastic behavior of the matrix proportionately varies with the addition of the bean pod ash particles. As the loading of bean pod ash fillers increases, the ability of the composites to absorb impact energy decreases since there is less ratio of the RLDPE matrix to fillers. However the results obtained remained within the standard level for biocomposites [
In this present work, some mechanical and microstructural studies have been carried out on the RLDPE/bean pod ash particles composite. From the results and discussion presented in the preceding section, the following conclusions can be made:
1) RLDPE reinforced with bean pod particles was successfully produced with casting method.
2) The optimum values of flexural strength were obtained at 140˚C, 12 minutes, 40 wt% CBPp and 6 Mpa.
3) The hardness values and tensile strengths of the composite are increased by the addition of beans pod ash particles to RLDPE composites.
4) Compressive properties of RLDPE matrix and composites are 13.00, 16.90 and 18.25 N/mm2 for the matrix, UBPp and CBPp composites.
5) The fairly uniform distribution of the bean pod ash particles in the microstructure of the composites is the major factor responsible for the improvement in the mechanical properties.
6) The obtained results of the developed composites have shown that the beans pod waste could be used as a biodegradable eco-friendly reinforcement.
M. C.Ekwedigwe,E. E.Nnuka,C. U.Atuanya, (2015) Experimental Evaluation of the Mechanical Properties of Recycled Low Density Polyethylene/Bean Pod Ash Particulate Bio-Composites. Journal of Minerals and Materials Characterization and Engineering,03,362-372. doi: 10.4236/jmmce.2015.35039