Improvement of Locally Produced Low-Density Polyethylene

In the present work, a polymer composite was fabricated by mixing LDPE with different wt% of pigment (Fe 2 O 3 and TiO 2 ) to obtain desirable properties in fabrication single screw-extruder was utilized , this mixing machine operated at a temperature between (150-170)C o .some of mechanical properties, such as tensile, impact, hardness and bending test were determined at different weight fraction of composite materials. It was found that the addition of pigment (TiO 2 and Fe 2 O 3 ) to the LDPE leads to increase the modulus of elasticity, tensile strength, tensile strength at break, shore hardness on other hand it decreases the % elongation at break, and for the impact strength.


Introduction
Low density polyethylene LDPE is the most important thermoplastic polymer, which is of practical use in many industrial applications.Polyethylene is the most important thermoplastic polymer.Low-density polyethylene (LDPE) is produced by the polymerization of highly purified ethylene at very high pressure in the presence of a trace of oxygen [1, 2, and 3].It is flexible and has a lower maximum temperature range than highdensity polyethylene.It finds use in many industrial applications and has good resistance to water, alkalis and inorganic salt and also has good resistance to moderate resistance of false oil and it has a moderate resistance to petroleum [4].

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Since the very early stages of the development of the polymer industry it was realized that useful products could only be obtained if certain additives are incorporated into the polymer matrix [5].Additives used in plastic materials are normally classified according to their specific function, rather than on a chemical basis [6].Mixtures containing one or more polymers and various ingredients such as stabilizers, filler, and colorant [7,8].Colorants are added to produce color in the polymeric part; they are separated into pigments and dyes [9].The particular color desired and the type of polymer will affect the selection of the colorants [10].Many workers investigated the phsico-mechanical properties of filled LDPE with additives.Malik.[11],studied the mechanical properties of PE extended to draw ratio in the (20-40) range have been determined and compared with corresponding properties of the polymers containing particulates including TiO 2 rutile, carbon black, iron oxide and mica.
Young.[12], studied the dispersion of titanium dioxide agglomerates with the linear low density polyethylene (LLDPE) by using a cone and plate device installed within a temperature controlled oven.Tibor and James [13], studied the effect of colorants on the mechanical properties of PE.Five pigment were investigated (titanium dioxide, cadmium yellow, iron oxide red, carbon black and phthalocyanine blue .Flores [ 14], studied the influence of filler structure on micro hardness of carbon black-low density polyethylene composites Surat and Yusuke [15], studied the solubility of carbon dioxide / low density polyethylene (LDPE)/titanium dioxide (TiO 2 ) composite was measured using a magnetic suspension balance (MSB) a temperature from 423 to 473 K 0 and pressure up to 15 Mpa.In the present work a composite material was fabricated using LDPE with different weight percentage of Fe 2 O 3 and TiO 2 by using single screw-extruder to obtain material with desire mechanical properties.

Experimental materials
In this work two main types of materials were used; Commercial LDPE of a density equal to 0.9235 gm/cm 3 .And inorganic pigment (TiO 2 rutile type and the particle size used equal (60.40) µm.and Fe 2 O 3 , the type of iron oxide used is hematite and the particle size is equal 40.62(µm))

Methods
The single-screw extruder machine was used to mix raw materials (LDPE and pigment).The compounding process involves mixing of different weight percent of LDPE and inorganic pigment.The weighted samples were inserted to a single screw machine at temperature ranging from (150-170) o C and rotation increases from (0-60) r.p.m..The compounding time involved was less than (5 min).After compounding process was completed (i.e., the melt became homogenous), the homogenous mixture then pressed in the hydraulic press by applying temperature and pressure at the same time the temperature applied to the upper and lower sides of mold while the sample was still under the applied pressure.(10MPa) and temperature (150 o C) for a (5min).A sample sheet with dimension (290x 205x4) mm was obtained .thetest were done on sets of the LDPE with different formulations as shown in table (1) The prime consideration in determining the general utility of a polymer is its mechanical behavior, tensile properties, impact strength, hardness and modulus of elasticity were carried out for examining the mechanical properties of the samples , The tensile strengths at break values were determined by using tensile test according to ASTM D638 [16].Shore D hardness was used to determine the hardness of the polymer materials, maximum Test Load: 50 N at Shore According to ASTM.Charpy test was used to determine the impact strength of the polymeric material, the samples of impact test were notched by (notch instrument) according to ASTM(D256-87) [16] .Three point system was used to determine the modulus of elasticity of low-density polyethylene with TiO 2 and Fe 2 O 3. to ASTM ( D790m-86)

Results and Discussion: Tensile Test
Figure (1) shows the variation of tensile strength ( ơ u ) of LDPE with different wt.%.of TiO 2 and constant Fe 2 O 3 content (7% wt) at different exposure times between (0-250) hrs. Figure (2) shows the variation of tensile strength 1063 (ơ u ) of LDPE with different wt.%.of Fe 2 O 3 and constant TiO 2 content ( 7% wt).From these figures (1-2 ) it is clearly seen that after the addition of pigment as a filler to LDPE the tensile strength increases with increase of wt% pigment (TiO 2 and Fe 2 O 3 ) added.This may be due to the fact that increase the wt.% of pigment particles will lead to a better adhesion between polymer and filler.Figure (3) illustrates the relation between the tensile strength at break ( ơ TB ) of LDPE at different wt.% of TiO 2 and constant % Fe 2 O 3 (7%).Figure ( 4) illustrates the relation between the tensile strength at break (ơ TB ) of LDPE at different wt.% of Fe 2 O 3 and constant % TiO 2 (7%).From these figures (3 and 4) it is clearly seen that increasing %pigment (TiO 2 and Fe 2 O 3 ) content leads to an increase in the fracture stress.This may be due to the binding forces between molecules .This leads to decrease in the elastic movement of polymer chain which leads to increase the fracture strength [6].This results is good agreement with results obtained by Tibor and and James [13]. Figure (5) shows the variation of % elongation at break (ζ B ) of LDPE at different wt.% of TiO 2 and constant % Fe 2 O 3 while (7%) Figure ( 6) shows the variation of % elongation at break (ζ B ) of LDPE at different wt.% of Fe 2 O 3 and constant % TiO 2 (7%) at different exposure times between (0-250) hrs.From these figures (5 and 6), it is clearly seen that increasing of wt.% of pigment particles (TiO 2 and Fe 2 O 3 ) lead to decrease in the %elongation at break, because the elongation at break of polymer composite depends on the elongation of filler and polymer [9], furthermore cracks can form either within or around the particles.Therefore, the voids and cracks do not transfer stress, making the material more compliable and thus lowering the material elongation.

Impact strength
Figure 7 shows the variation of impact strength of LDPE at different wt.% of pigment particle (TiO 2 ) and constant at % Fe 2 O 3 (7%).Figure 8 shows the variation of impact strength of LDPE at different wt.% of pigment particle (Fe 2 O 3 ) and constant % TiO 2 (7%).The results show that increasing the wt.% of pigment TiO 2 and Fe 2 O 3 lead to decrease in the impact strength, also increase of pigment causes a decrease in samples toughness, because the addition of pigment particle causes an increase in the strain rate which leads to carry part of fracture energy and it will act as crack growing that leads to fracture and it will distribute the applied fracture stress.Therefore the toughness of the polymer decreases and its ability to absorb and dissipate energy decrease, thus the polymer needs low impact energy to fracture [7].
Hardness Test: -In the present work Durometer hardness type (shore -D) was used to measure the hardness.Figure 9 shows the variation of hardness test of LDPE at different wt % of TiO 2 and at constant % Fe 2 O 3 (7%).Figure 10 shows the variation of hardness test of LDPE at different wt % of Fe 2 O 3 and at constant % TiO 2 ( 7%). Figure (9 and 10) show that the shore hardness increases with the increasing of wt.% of pigment particle (Fe 2 O 3 and TiO 2 ) ranging between (9-15) %.As the wt.% of pigment added increases the ability of polymer to resist plastic deformation increase [10].It is well known that the hardness originally depends on some important factors such as: type of the linking forces between the molecules and type of the surface and other effective conditions.thisresults in good agreement with result obtained by Malik [11].

Bending Test
The modulus of elasticity (E) 1s a measure of the stiffness or rigidity of materials depending upon strength of interatomic bonds and compositions .Figure 11 illustrates the relation between the modulus of elasticity of LDPE at different wt.% of TiO 2 and constant % Fe 2 O 3 (7%).Figure 12 illustrates the relation between the modulus of elasticity of LDPE at different wt.% of Fe 2 O 3 and constant % TiO 2 (7%).From these figures (11 and 12) it is clearly seen that the increase of wt.% of pigment particles (TiO 2 and Fe 2 O 3 ) leads to increase in the modulus of elasticity.This increase in modulus of elasticity is due to the increase of linking force between the molecules of the matrix and thus become more elastic which leads consequently to a smaller deformation of sample, ultimate increase of modulus of elasticity [5].