Mechanical and Morphological Properties of HDPE: PP and LDPE: PP Polymer Blend Composites Reinforced with TiO 2 particles

In this research two groups of polymer blends have been prepared First group included (High density polyethylene (HDPE): Polypropylene (PP))While the Second group (included Low density polyethylene (LDPE): Polypropylene (PP)) both groups prepared withpolypropylene of (20% and 80%). From the results of tensile test for the prepared blends it has been showed that the optimum blending ratio was (20%LDPE:80%PP and 20%HDPE:80%PP) which thenreinforced with (2, 5 and 8wt %) oftitanium dioxide (TiO 2 ), particle size (0.421µm). Titaniaparticles were mechanically mixed with the polymers prior tomelt mixing for better dispersion. Polymerblend composites were obtained by using single screw extruder. Results showed that mechanical properties increased as titania content increased except elongation.Furthermore the result recorded highest values ofimpact strength and fracture toughness at2%wt TiO 2 which is 312 Mpa and 572.8Mparespectively,for the polymer blend (20%HDPE: 80%PP) composite and for the polymer blend (20%LDPE: 80%PP) composites the impact strength and fracture toughness are 262.5Mpa and 468 Mpa respectively.The mechanical properties values of 20%HDPE: 80%PP is higher than 20%LDPE: 80%PP polymer blendcomposites. Scanning electron microscopy (SEM) imagesshowed that there isbonding developed between TiO 2 and polymer blends in some regions.


‫و‬ HDPE: PP ‫البوليمري‬ ‫الخالئط‬ ‫لمتراكبات‬ ‫المجهرية‬ ‫و‬ ‫الميكانيكية‬ ‫الخواص‬ ‫ة‬ ‫التيتانيوم‬ ‫اوكسيد‬ ‫بدقائق‬ ‫المقواة‬ LDPE: PP
A new approach to the science and technology [1].Blending of two polymers in a possible way to tailor their individual properties in a single material.The properties of polymer blends strongly depend on their morphology which is determined by the size distribution and shape of distributed particles [2,3].Some studies showed that uncompatiblized immiscible polymer blends provide synergy of mechanical properties when the processing and compositional parameters are near optimum values [4][5][6].The incorporation of fillers into thermoplastics is another method widely used to enhance certain properties.The degree of property enhancement depends on the filler type, filler particle size and shape, the content of filler (Albano et al. [7] analyzed the effect of CaCO3 on blend of PP/HDPE found that the addition of this blend at 30wt% did not improve the mechanical properties of the blend) and most importantly the filler origin [8][9][10].Studies dealing with polymer blend reinforced with rigid filler to give three-phase polymer composites have been increased considerably during the last few years [11][12][13].Michel A. H.,and Hongbo Li investigated the structure development in the starch gelatinization and thermoplastic starch mixing with PE, PP, PS and showed the tensile strength, tensile modulus and elongation at break of the blend were decreased by addition of the thermoplastic starch [13].The objective of this study was to investigate the effect of titania particles content on the mechanical and morphological properties of the two types of polymer blendsbased composites.

Materialsand Experimental Methods
In this research three types of polymer materials used which were provided from the National Company for Plastic and Chemical Industries / Zaffrania -Baghdad.The polymer materials are High density polyethylene (HDPE), Low density polyethylene(LDPE)and Polypropylene (PP).Physical properties data for each polymer is given in Table (

Blending
Polymer blends of (HDPE:PP) and (LDPE:PP) both groups prepared with polypropylene of (20% and 80%) were melted in a single screw extruder machine with a screw L/D of 30:1 (Iraqi Al-Forat Company 2004 Extruder) to make strips of polymer blends with 1.5mm thickness.Tables 2 and3 show the compositions and the extrusion parameter respectively for both polymer blends and composite prepared.Samples prepared by compression moulding technique including locating previous extrudate blendstrips in a mold made of steel to have the suitable thickness for inspections which is previously heated at 160ºCfor one hour, compression technique carried out at pressure (300 kgf/cm 2 ) for (5 -10) minutes depending on the type of the blend.

Mechanical test
Samples were prepared for the tensile test in accordance with ASTM D638-87 [14].A computerized universal testing machine model (WDW-200D Jinan Shijin Group company-china) was used to conduct a test at a constant cross head speed of the order 10 mm/min at room temperature.Tensile load was applied till the failure of thesample and stress -strain curve was obtained.Each sample was tested for 3 times and average results have been reported.Impact test is performed at room temperature according to ASTM ISO 179 [15].Izodcharpy tension impact (measurement test machines Inc,Amityville-New York).Bending modulus measured from three point test, this test is performed according to ASTM D-790-78 [14] at room temperature.Hardness test carried out on a Durometer shore D scale according to ASTM D-570 [15].A creep test is performed under a constant applied load (40N) at room temperature according to BS 1178 [15].

Results and discussion:-Tensile test of HDPE: PP and LDPE: PP blend and its composite.
Polymer blends with differentweight percentages of polypropylene (20% and 80%) in bothblends (HDPE: PP) and (LDPE: PP) have been studied.The results of ultimate tensile strength and young modulus are shown in Fig. (3 a,b) respectively these figuresshowed that 80%wt of PP is the best ratio in the two types of blends (HDPE: PP) and (LDPE: PP).According to these results, polymer blends which are (20%HDPE: 80%PP) and (20%LDPE: 80%PP) are selected as the optimum polymer blend ratio and reinforced with chosen ratios (2, 5 and 8%) of titania particles.The stress -strain behavior of the net blends (20%HDPE: 80%PP) and(20%LDPE: 80%PP)and its composites are shown in Fig. (4a, b) respectively.It can be noticed that as TiO2 content increased in the blend there will be change in the behavior from hardand tough for neat blends to hard and strong for polymer blends (20%HDPE:80%PP) which reinforced with 8%wt of titania particles.d) an increase in ultimate strength values with the addition of TiO2 particles for the two groupsof blends and similar result is observed in each of fracture strength and young modulus, but differs in elongation and this related to the nature of TiO2 particles which are stiffer and stronger than the continuous polymer blend matrix [10].And it is noted from these figures that the ultimate strength, fracture strength and young modulus values for the (20%HDPE: 80%PP) blend composite is higher than the (20%LDPE: 80%PP) blend composite that may be related to the difference between both types of PE in molecular chain structure, HDPE has very little branching on the main chains, and so the chains can pack more closely together to increase crystallinity and strength [14].

Bending test of polymer blend composites
The results of three -point bending test show that the elasticity modulus of bending (E bend) values for the composites increased as TiO2 particles content increased for both types of blends (20%HDPE: 80%PP) and (20%LDPE: 80%PP) as shown in the Fig. (6) The incorporation of TiO2 with the polymer blend leads to higher bending modulus due to the interfacial reaction between polymer blend and TiO2particles,andthese values for the (HDPE: PP)blend composites is more than (LDPE: PP) blend composites.

Impact test of polymer blend composites
It has been realized from Fig. (7 a) that there is a high increment of impact strength at 2% TiO2 particles when it is compared with thenet blends in both polymerblends, but this increment has decreased gradually as TiO2 ratio increased to higher than 2% ratio, this is due to the fact that TiO2 particles are ceramic particles have a high hardness compared with the polymer materials, so that the impact strength decrease when it is added in a high ratio [10].So the best ratio that increased the impact was at 2% TiO2 and the rate of increment were 125% and 150% for both 20%LDPE: 80%PP and 20%HDPE: 80%PP blend composite respectively as shown in the reach to high values at 2%TiO2 ratio, then the rate of increment were decreased, but fracture toughness values for two group of polymer blend composites are larger than their matrix (net polymer blends).Incorporation of TiO2 particles into polymer blends leads to higher fracture toughness values due to the interfacial reaction especially when it is added in slight ratio, and provides an effective barrier for the advancing cracks [17].Also it has been noted from both Fig.

Shore D Hardness of polymer blend composites
The hardness values of Shore D increases with the increasing of TiO2 particles content in the blends as shown in the Fig. (8) .This is related to the titania particles which are ceramic particles have a high hardness compared to polymer blends.Furthermore hardness values of (20%HDPE: 80%PP: TiO2)slightly higher than hardness values of (20%LDPE: 80PP:TiO2) composites due to the difference in the chain structure for two type of PE [16].Also as shown in Fig. (10) creep modulus (the ratio of the initial applied stress to the creep strain ε(t)after a particular time and at a constant temperature of testing [16] ) of blend composites increases as reinforcement titaniaparticles increased.Furthermore, it has been also realized from Fig. (10) That creep modulus of (20%HDPE:80%PP) blend compositesis higher than (20%LDPE:80%PP) blend composite this related to the difference in the molecular chain of both types of PE.
Fig. (7a), while Fig. (7 b) showsfracture toughness values of blends were increased as TiO2 particles added to the blends and (7 a and b) that impact strength and fracture toughness values of composite materials for (20%HDPE: 80%PP)blend are higher than the other blend (20%LDPE: 80%PP).

Particle Size Distribution of TiO2 Powder Particle
size distribution of TiO2was carried out using laser diffraction particle size analyzer type (SHIMADZCE SAID-2101) inScience and Technology ministry/Baghdad.The result of particle size distribution is shown in