Effect of Filler Content on the Mechanical Properties of High-density Polyethylene (HDPE)


Academic Paper, 2019

9 Pages, Grade: N/A


Excerpt

Table of Contents

INTRODUCTION

MATERIALS AND RESEARCH METHODOLOGY
Collection and preparation of the materials
Composite processing
Hardness testing
Flexural testing

RESULTS AND DISCUSSIONS
Effect of different types of fillers on the impact strength of the composite
Effect of different types of fillers on the flexural strength of the composite

CONCLUSION

Funding/Acknowledgments

ABSTRACT

In this study, the effect of various fillers (oyster shell, periwinkle shell, okpa membrane, and cashew membrane) on the mechanical properties of high-density polyethylene (HDPE) has been investigated. Results indicate that the fillers improved both the impact strength and the flexural strength of the composite. The impact strength increased with decrease in particle size, which was attributed to the fact that particulate fillers with smaller particle sizes are more dispersed in the polymer matrix than those of big particle sizes. On the other hand, the flexural strength showed optimum enhancement at 1000 µm filler size and 37.5 wt.% filler concentration. Above 37.5 wt.% filler concentration the flexural strength decreased. Comparatively, it was found that cashew membrane gave the highest enhancement in mechanical properties of the high-density polyethylene at 1000 µm filler size and 37.5 wt.% filler concentration.

KEY WORDS: High-density polyethylene (HDPE), fillers, impact strength, flexural strength

INTRODUCTION

Natural filler-reinforced polymer composites have attracted more attention recently due to benefits such as cost effectiveness, lighter weight, and renewability of the fillers. Despite the benefits, natural filler composites face some challenges that prevent their widespread use. For instance, filler-polymer incompatibility has been the subject of previous studies [1]. This incompatibility is caused by the hydrophilic nature of the filler and the hydrophobic nature of many polymers used [2-5]. Moreover, the presence of hemicellulose, lignin and other impurities have also been found to cause a lack of adhesion between filler and polymers. However, polyethylene mixed with hydrophilic fillers has shown improved compatibility [6-8].

The physical and mechanical properties of natural filler composites largely depend on the type of matrix, content and properties of the reinforcement fillers and filler–matrix interaction [8-10]. Better dispersion of the filler can be achieved by effective mixing of the components and a proper compounding process. It has been reported that by adding filler in the polymer material, the mechanical properties of the composite such as the strength can be further enhanced [2-4]. However, it had also been mentioned that the strength of the composites decreased when the filler content exceeded a critical value [10]. One of the main concerns for the use of natural fiber or filler reinforced composite materials is their susceptibility to moisture absorption and the effect on physical, mechanical and thermal properties. All polymer composites absorb moisture in humid atmosphere and when immersed in water. The effect of absorption of moisture leads to the degradation of filler matrix interface region by creating poor stress transfer efficiencies resulting in a reduction of mechanical properties.

In this research work, natural fillers such as oyster shell, periwinkle shell, okpa membrane, and cashew shell were used. These biomaterials contain large number of organic compounds and small number of inorganic materials. The effect of filler concentration and particle size on the properties of high-density polyethylene were also examined.

MATERIALS AND RESEARCH METHODOLOGY

Collection and preparation of the materials

High-density polyethylene (HDPE) was purchased at Indorama Eleme Petrochemical Onitsha, Nigeria. Oyster shells, periwinkle shells, okpa membrane, and cashew membrane were sourced from various locations in Awka, Nigeria, and were sun dried for one week. Various particle size of the fillers (850, 1000 and 1800 µm) were used throughout the experiment. A fixed 100 g of HDPE was used while for each filler type and particle size, its concentration was varied from 16 to 50 wt.%.

Composite processing

The HDPE was melted and homogenized with each of the fillers in an injection moulding machine. The operating pressure and temperature of the injection moulding machine was 150 MPa and 160 ℃ respectively, and the process time for each sample was 1 minute approximately. The raw materials to be compounded were fed into the injection moulding machine through the hopper. To get a satisfactory moulding, the shot size or shot capacity is fed into the machine.

Hardness testing

Hardness testing was performed by measuring the permanent depth of the indentation. The Brinell hardness testing method was used which consists basically of indents test material with a 10 mm diameter hardened steel or carbide ball subjected to a load of 500 - 3000 kg. The Brinell hardness test was conducted on 400 mm (span) × 40 mm (width) × 5 mm (thickness) of each of the samples using a manually operated universal testing machine. A hardened steel ball with a diameter of 10 mm was used in performing the test. The indentions on the specimens were measured (diameter-wise) and an appropriate mathematical method was used for conversion to obtain the Brinell hardness values.

Flexural testing

The 3-point flexure test is the most common for polymers. Flexural properties were carried on composite samples with dimensions 125 mm (span) × 25 mm (width) ×5 mm (thickness) using an FSA (MODEL: TUE- C 100) universal testing machine according to ASTM 790-90 standard.

RESULTS AND DISCUSSIONS

Effect of different types of fillers on the impact strength of the composite

The effect of filler type on the impact strength of the high-density polyethylene is shown in figures 1a, 2a, 3a and 4a. These figures show that the impact strength of the filled high-density polyethylene increased with the filler content (irrespective of the filler type). Therefore, the addition of the fillers into high-density polyethylene matrix improves the toughness of the material. Further, these figures revealed that the impact strength of the composite has inverse relationship with the filler particle size. Thus, as the filler particle size increases, the impact strength decreases. This was attributed to the fact that particulate fillers with smaller particle sizes are more dispersed in the polymer matrix than those of big particle sizes. Interestingly, the maximum impact strength for the fillers did not vary significantly with the filler type, as the range is between 11.5 to 12 J/m for 800 µm particle size (see figures 1a, 2a, 3a and 4a). On the other hand, a wider variation in flexural strength with filler type was observed (discussed later). Therefore, the enhancement of impact strength of high-density polyethylene did not improve significantly, irrespective of the filler type used (i.e. oyster shell, periwinkle shell, okpa membrane or cashew membrane)

Effect of different types of fillers on the flexural strength of the composite

The effect of the filler type on the flexural strength of the high-density polyethylene is shown in figures 1b, 2b, 3b and 4b for the various fillers. Generally, these figures indicate that at any particle size considered, the flexural strength of the composites increased with increase in filler contents up to 37.5 wt.%. This trend is the same irrespective of the filler type. Beyond this value, however, the flexural strength decreased owing to poor load/stress transfer. The increase in flexural strength with filler content up to 37.5 wt.% may be due to the fact that when the fillers are added to the polymer, they act like binders which stiffens the elasticity of the polymer matrix and increase the ability of the composite to absorb and dissipate energy. It appeared that the flexural strength was best enhanced when the filler particle size was 1000 µm. Moreover, the impact strength at 800 and 1000 µm did not vary significantly at all filler particle sizes (see figures 1a, 2a, 3a and 4a), whereas their flexural strength varied significantly below 37.5 wt.% filler concentration. Hence flexural strength is more sensitive to the particle size of the fillers. Overall, one can deduce that cashew membrane of particle size 1000 µm at 37.5 wt.% filler content gave the highest flexural strength of 34 N/m2 (see figure 2b). Comparatively the maximum flexural strength of the composite increased in the order: cashew membrane > okpa membrane > periwinkle membrane > oyster shell. Considering that the impact strength of the materials did not vary significantly with filler type, this study suggests that cashew membrane is potentially the best filler for the high-density polyethylene.

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Details

Title
Effect of Filler Content on the Mechanical Properties of High-density Polyethylene (HDPE)
College
Nnamdi Azikiwe University Awka
Grade
N/A
Author
Year
2019
Pages
9
Catalog Number
V509955
ISBN (eBook)
9783346077813
Language
English
Tags
effect, filler, content, mechanical, properties, high-density, polyethylene, hdpe
Quote paper
Ebuka Udeaja (Author), 2019, Effect of Filler Content on the Mechanical Properties of High-density Polyethylene (HDPE), Munich, GRIN Verlag, https://www.grin.com/document/509955

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