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Cassava Peel - Cowpea Hull Blended Agro-Waste Fillers: Effect on

Mechanical, Morphological and Degradation Properties of

Polypropylene

*Nwokoye, J.N., Okoye, P.A.C. and Chris-Okafor, P.U.

Department of Pure and Industrial Chemistry, Faculty of Physical Sciences, Nnamdi Azikiwe University, Awka, Anambra

cassava peel and cowpea hull were homogeneously mixed at the ratio of 50:50 to form the hybrid filler. The virgin pellets of PP

and recycled polypropylene (rPP) were filled with varying weight percentages (5, 10, 15, 20) of the blended filler and the

composites produced via injection moulding technique. The mechanical properties; tensile strength, percentage elongation at

break, hardness, compressive strength, and shear modulus were studied according to American Society for Testing and Materials

(ASTM) standards. The morphological properties were studied with a Scanning Electron Microscope at 10,000 magnifications.

The degradation study was achieved by soil burial method for one hundred and eighty (180) days period. The results of the

mechanical properties showed increased tensile strength, hardness, compressive strength and shear modulus while the percentage

elongation at break decreased as the filler load increases. The micrographs showed that the virgin PP has better adhesion and

interfacial bonding with the filler than the rPP. Biodegradation test revealed a reduction in the mass of the composites after one

hundred and eighty (180) days burial period indicating that the composite is degradable. From the findings, the cassava peel-

produced and used polymers include; polyethylene, polypropylene, polystyrene, Poly (Vinyl chloride). Polyethylene and

polypropylene are the most widely produced polymer globally because they are utilized for many applications such as packaging,

electrical insulations, construction and daily consumer products (Shaharuddin et al., 2017). Although most of these polymeric

materials appear to be single materials from their names, but they usually contain additives like modifiers, lubricants, fillers,

flame retardants, plasticizers, heat and light stabilizers or aesthetic agents to achieve desired physical, mechanical or chemical

properties on the finished products (Fried, 2009; Sindhu, 2010). They show remarkable stability under many environmental

conditions which leads to accumulation and visible pollution (Glaser, 2019). This visible pollution has led to research on

development of sustainable and environmentally friendly green materials based on renewable resources, recyclable and

biodegradable (Thompson et al., 2009). The renewable materials which are basically organic biomass are capable of degrading

within days/ weeks or months.

interaction, particle size, fibre population and distribution of the filler particles within the matrix. Ofora et al., (2016b) studied the

Mechanical Properties of Dioscorea Dumetorum Starch Filled Linear Low Density Polyethylene Composites. The experimental

test on mechanical properties such as tensile strength, elongation at break, hardness, flexural and compressive strength showed an

increase in the tensile strength, hardness, flexural and compressive strengths with reduction in elongation at break. Also, the

results showed that the filler had positive impacts on the mechanical properties as the filler volume increased and the optical

microscopy showed an improvement on the dispersion of the filler in the composite matrix as the filler volume increases. Aisien

and Ikenebomhe, (2017) investigated the effect of inorganic fertilizer N.P.K and microbial inoculants on the biodegradation

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process of cassava peel for twenty weeks at waste dump site. The results showed increased pH, decreased total soluble

carbohydrate concentrations, protein, lipids, starch, cyanide and cellulose. This indicates biodegradation of cassava peels.

Ogudo, Chris-Okafor, Nwokoye and Anekwe, (2021) worked on mixed agro-waste biocomposites of low density polyethene;

Onyenweaku, Nwokoye and Chris-Okafor, (2021) studied the mechanical and surface morphology properties of low density

polyethylene composites filled with organic materials. Blends of coconut husk and mango seed shell were used as agricultural

wastes. The results showed that the fillers had positive impacts on the flexural strength and hardness, while there were negative

impacts on tensile strength and compression strength. Nwokoye, Okoye and Chris-Okafor, (2024) worked on impact of hybrid

biomass fillers on the physico-mechanical and degradation properties of utility polymers which involved the use of varying

percentage filler load of hybrid cassava peel-rice husk filler on low density polyethylene and polypropylene. The results showed

improved tensile strength, compressive strength and hardness, reduced percentage elongation at break, irregular shear modulus,

zero effect on LDPE creep rate, irregular creep behavior for PP composites and improved degradation of the composites.

From the reviewed literature, it could be seen that no research involving cassava peel- cowpea hull blend with any polyolefin has

been done.

sieved locally and repeatedly using a grain mill machine M6FFC-270 and muslin cloth respectively to a fine powder of 75μm

mesh size.

Preparation of Composites

The fine powders of cassava peel and cowpea hull were manually mixed at the ratio of 50:50 at room temperature to form

homogeneous blend filler. The virgin crystalline pellets of PP and recycled pellets of polypropylene (rPP) were weighed at 200g,

190g, 180g, 170g, and 160g respectively and mixed with the blended filler of 0g, 10g, 20g, 30g, and 40g respectively,

corresponding to 0%, 5%, 10%, 15%, and 20% filler loading. The homogeneous filler and polymer matrix mixture was put into

the hopper of a TU150 200 gram injection molding machine. Production of the composites at 288

Mechanical Properties Analysis of the Composites

Hardness Test

This measures the depth of indentation on the surface of the composite when pierced with an indenter. The surface hardness was

Shear Strength

This is the measure of the materials ability to withstand forces that cause its internal structure to slide against itself. The shear

strength of the composites was determined according to the ASTM D-732 using the Hounsfield Monsanto Tensometer 8889

Made in England. The test piece was measured to 20mm x 20mm x 3.2mm.

Compressive Strength

This refers to a composite's ability to withstand compression. It was determined according to the ASTM D-695 using the

Hounsfield Monsanto Tensometer 8889 Made in England. The test piece was measured to 20mm x 20mm x 3.2mm.

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Morphological Analysis

Scanning Electron Microscope (SEM) model: JEOL-JSM 7600F.

IV. Results and Discussion

Mechanical Properties

The results of the mechanical properties of the PP and rPP composites with cassava peel-cowpea hull fillers are shown in the

figures below.

Tensile Strength

Figure1. Effect of filler loading on the tensile strength of PP and rPP composites

From Figure 1, the composites showed initial decrease in the tensile strength before an increase as filler content increases till

maximum then subsequent decrease with increase in filler loading. The initial decrease could be as a result of insufficiency of the

filler content. The peak values were observed at 10wt% filler load for rPP and 10wt% to 15wt% for PP. This increase in the

This measures the level a material can be drawn or stretched as a percentage of its original length.

Figure2. Effect of filler loading on percentage elongation at break of PP and rPP composites

Figure 2 shows that the percentage elongation at break decreased with increase in filler loading. This indicates that increasing

filler loading decreased the ductility/ elasticity of the polymer composites and makes it stiffer. This decrease indicates the filler

ability to facilitate stress transfer from filler to matrix. This is in line with Chris-Okafor et al., (2018); Nwokoye et al., (2024).

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Hardness

Figure3. Effect of filler loading on the hardness of PP and rPP composites

Figure 3 reveals an overall increase in hardness as the filler content increases for PP and rPP composites except for PP composite

at 10wt% that showed reduced hardness. This is an indication that the fillers enhanced the hardness of the composites which

Figure 4 shows that the composites' compressive strength increased, with the highest compressive strength at 10wt% filler load

for rPP increasing by 44.6%. This increase could be attributed to the filler reinforcing characteristics, which improved the

composite's mechanical properties due to its cellulosic nature, which is in agreement with the work of Ofora et al., (2016a), Ofora

et al., (2016b) and Nwokoye et al., (2024).

Shear Modulus

Figure5. Effect of filler loading on the Shear modulus of PP and rPP composites

In Figure 5, the shear modulus increases as the filler loading increases. This increase suggests that the fillers increased the rigidity

of the composites and enhanced the load-bearing ability of the material thus a larger force is required to deform the composites

along the plane of the direction of the force. This is in agreement with the work of Ogudo et al., (2021). Only the shear modulus

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Morphological Analysis

increases while the filler matrix interaction decreases. Thus, the strength of the rPP composites after 10wt% filler load decreases

as the filler load increases due to increase in voids that acts as fracture initiation site and reduced interfacial contact between the

hybrid fillers and the polymer matrix. This could be attributed to some factors such as the difference in the polarity of the filler

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to higher degradation of the composites. This observation corroborates the research findings of Chamas et al., (2020), Ogudo et

al., (2021) and Nwokoye et al., (2024). These authors discovered that biodegradability of composites were well pronounced and

because they are cheaper and readily available.

https://dx.doi.org/10.4314/v33i1.14

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13. Onuegbu, G. C. and. Igwe, I. O. (2011). The Effects of Filler Contents and Particle Sizes on the Mechanical and End-

Use Properties of Snail Shell Powder Filled Polypropylene. Materials Sciences and Applications, 2(7): 810-816. doi: