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Journal of Saudi Chemical Society (2015) 19, 88–91 King Saud University Journal of Saudi Chemical Society www.ksu.edu.sa www.sciencedirect.com ORIGINAL ARTICLE Mechanical properties of filled high density polyethylene Moayad N. Khalaf * Chemistry Department, College of Science, University of Basrah,...

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Journal of Saudi Chemical Society (2015) 19, 88–91

King Saud University

Journal of Saudi Chemical Society www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Mechanical properties of filled high density polyethylene Moayad N. Khalaf

*

Chemistry Department, College of Science, University of Basrah, P.O. Box 773, Basrah, Iraq Received 8 August 2011; accepted 24 December 2011 Available online 8 January 2012

KEYWORDS Polyethylene (PE); Mechanical properties; Composites

Abstract Mechanical properties of (HDPE M624) with three filler (inorganic and organic) composites were assessed with respect to the effect of the filler content. The filler varied from (5% to 25%) by weight in the composite. Obvious improvement in the mechanical parameters was recorded depending on the filler type and mesh size. The mechanical properties of loaded compressed sample have been evaluated through several parameters concerning the elastic deformation based on measuring the load–elongation characteristics. The behavior of stress–strain curve was analyzed in terms of cold drawing model. No experimental difficulties appeared at any mixing ratio, and these difficulties were due to the separation in phase which makes the sample possible for processing in the normal extruders. ª 2012 Production and hosting by Elsevier B.V. on behalf of King Saud University.

1. Introduction Several manufacturers are producing wood–thermoplastic composites from recycled materials. In a little over a decade, the use of plastics and fiber–thermoplastic composites for decking has grown to about 6% of the exterior decking market (Smith and Carter, 1999). Larger markets within the building industry could be developed, such as the roofing market, but lack of durability performance data and reluctance of home builders to utilize undemonstrated products have hampered market development. Thermoplastics have several favorable characteristics as components in composites, including recycla* Tel.: +964 7801042860; fax: +964 40417970. E-mail address: [email protected]. Peer review under responsibility of King Saud University.

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bility, moldability high specific strength and modulus, low cost, low density, and low friction during compounding (Rietveld and Simon, 1992). Wood–polymer composites have excellent dimensional stability under moisture exposure and better fungi and termite resistance (Maldas and Kokta, 1991; Verhey et al., 2001). In this paper we investigated, mechanical properties of (HDPE with calcium carbonate, fiber glass and lignocellulose) for different filler weight percentages (5–25%). Parameters such as tensile strength, Young’s modulus, elongation at break, impact and Shore D have been measured at room temperature. The results were analyzed based on (stress–elongation) relationship. 2. Experimental 2.1. Materials High density polyethylene injection of grade (SCPILEX M624) (MI = 6.0 g/10 min) and (density = 0.960 g/cm3) was sup-

http://dx.doi.org10.1016/j.jscs.2011.12.024 1319-6103 ª 2012 Production and hosting by Elsevier B.V. on behalf of King Saud University.

Mechanical properties of filled high density polyethylene 25 20 Stress (N/mm2)

plied by the state company for petrochemical industry (SCPI). Lignocellulose (LC) filler from the round basis of date palm leaf cultivaf content (27.23%) lignin (Mengeloglu and Karakus, 2008). Calcium carbonate (CC) was supplied by Omya company, France (mesh size = 2.5 lm), fiber glass (FG) was supplied by ppg industries Inc. The lignocellulose filler was dried at 110 °C for 1 h before being milled in laboratory grinder to (mesh size = 45 lm).

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Mixer-600 attached to Haake Rheocord Torque Rheometer supplied by Haake Company was used to prepare the composite polyethylene. The tensile testing measurements were carried out on Instron 1193 instrument at room temperature according to ASTM D638 (Bledzki et al., 2007, 2011; Bukhaev and Sabarwal, 1984). Specimens were tested from each sample. Tensile-impact strength test was conducted according to ASTM D1822-93 by Tinius Olsen Testing Machines Co., Willow Grove, PA. Durometer readings were performed according to ASTM D2240-97. The Durometer hardness tester (Shore Instrument and MFG Co., Freeport, NY) consists of a pressure foot, an indentor, and an indicating device. Two types of Durometers most commonly used are Type A and Type D. Due to the slightly harder sample being examined; the Type D gauge was used. 2.3. Preparation of polyethylene composite The filler was mixed with 60 g of polyethylene using mixer-600 attached to Hakke rheocord meter with the following condition: mixing time 15 min, mixing temperature 160 °C and velocity 32RPM. The percent of fillers in the filled high density polyethylene is shown in Table 1. In order to prepare the molded specimens for mechanical analysis, the compounded polyethylene is introduced into a laboratory compressor less than 5 ton at 175 °C for (3 min). The pressure was then raised gradually up to 15 ton for (6 min), finally cooled to room temperature. 3. Results and discussion Stress–strain relationship in polymers is considered as complex dependencies, and is not linear in nature. Tensile characteristics (tensile strength at yield, % elongation and Young’s modulus) have been determined from the stress–strain curve. Typical curve shows the effect of the filler on the HDPE mechanical properties was shown in Fig. 1 which was of the

Figure 1 Typical stress–strain curve for 5% of LC filler in polyethylene.

(stress–strain) curve of HDPE loaded with 5% LC filler measured at a constant rate loading at room temperature. Stress–strain curve describes the material characteristics and is less dependent on the arbitrary choice of specimen profile. It is well known that polyethylene belongs to (soft and tough polymers) where this behavior has been characterized with low modulus and low yield stress. Fig. 2 presents the tensile strength (TS) data of the HDPE/filler composite for the three fillers used in this work. Analyzing the data of TS for the three given fillers, it can be observed that an increase in fillers’ (CC and LC) concentration leads to substantial increase in the properties up to an optimum concentration of (CC = 5% and LC = 15%) above which these properties tend to decrease. For the FG with fiber length (1–3 mm) we expect poor dispersion in the polymer matrix which causes decrease of the TS of the composite for which the polyethylene/FG has less value than the polyethylene matrix for all concentration of the FG filler. The reinforcing ability of the fillers did not just depend upon the mechanical strength of the fillers but on many other features, such as polarity (types of functional group) of the filler, surface characteristics and particle size of the fillers (Bukhaev and Sabarwal, 1984; Lewis and Nielson, 1970). These results are comparable to those reported by Bledzki et al., 2011. Considering that the fillers’ efficiency in the mechanism of these HDPE/(CC and LC) composites can be defined as a function of maximum TS properties’ improvement achieved indicates the best dispersion of CC filler due to the small particle size with large surface area at low concentration (5%). Above this concentration agglomeration of the filler takes place, while for the LC with higher particle size (45 lm) the functional groups (–OH, –OCH3, –C‚O) being the control 27 LC

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Figure 2

Effect of filler on the tensile strength of HDPE M624.

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Figure 3

Effect of filler on the Young modulus of HDPE M624.

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Figure 4

Effect of filler on the % elongation of HDPE M624.

factor that increases the interfacial adhesion between the HDPE and the LC filler for which the TS increases to optimum concentration (15%) (Bajwa et al., 2011). Figs. 3 and 4 show the Young’s modulus and elongation at break of the HDPE/ fillers. The data show improvement of the young modulus of the composite and dramatic decrease in the %elongation for all fillers till below 15%. After 15% of filler, it is clear that there is no significant effect on %elongation. This behavior for the composite is a result of the improved stiffness of the composites which was attributed to interaction between the polyethylene and fillers and also the fillers has less elongation value than the polyethylene (Al-Hajjaj and Saki, 2010). Fig. 5 shows the Impact strength of the composite. The impact strength value of the HDPE/(CC and LC) was dramatically decreased than the HDPE value due to the types (particle form) of the filler (Yang et al., 2007). While for fiber glass with 60

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Figure 6

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Effect of filler on the Shore D of HDPE M624.

fiber length (1–3 mm) the impact strength of HDPE/FG was improved (Bledzki et al., 2007), the impact resistance of fiber-reinforced composite depends on fiber rigidity, interfacial stress resistance and fiber aspect ratio. The strength of the matrix, the weakest part of the material, should be related to the failure process. The involvement of fibers in the failure process is related to their interaction with the crack formation in the matrix and their stress transferring capability. The total energy dissipated in the composite before the final failure occurs is a measure of its impact resistance (Mohanty et al., 2001). The total energy absorbed by the composite is the sum of the energy consumed during plastic deformation, the energy needed for pulling out the fiber out of the matrix and the energy needed for creating new surfaces for that reason the impact strength of the HDPE/FG was increased. Fig. 6 shows the hardness of the composite. The hardness is defined as the resistance of a material to deformation, particularly permanent deformation, indentation, or scratching. The Durometer hardness test is used for measuring the relative hardness of soft materials. The test method is based on the penetration of a specified indentor forced into the material, under specified conditions. Higher Durometer hardness readings are considered positive results. From the data it was evident that the HDPE/FG has the higher than the other fillers (CC and LC) which was in agreement with the data of the Young modulus (Mengeloglu and Karakus, 2008; Khalf and Ward, 2010). 4. Conclusion Lignocellulose (LC) filler from the round basis of date palm can be a potential candidate for the synthesis of natural reinforced composites. It has been found that the composite materials can possess appreciable mechanical strength compared with other fillers. Percent loading of the lignocellulose filler has been found to affect the magnitude of the composite. Eco-friendly, low density and high mechanical properties of the composite have made them good reinforcing materials for the synthesis of composite materials.

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References

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Effect of filler on the impact strength of HDPE M624.

Al-Hajjaj, A., Saki, T., 2010. Improving the design stresses of high density polyethylene pipes and vessels used in reverse osmosis desalination plants. J. Saudi Chem. Soc. 14, 251–256.

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