Elaboration Of Rubber Profiles For Auto Industry

Elaboration of Rubber Profiles for Auto-industry

A.A.Yehia*, A.I. Khalaf, and D.E.El Nashar,

Polymers and Pigments Department, National Research Centre, Cairo 12622, Cairo, Egypt

Abstract

EPDM is extensively used in automotive applications, especially for the automotive profiles. EPDM is favored over NR and SBR; due to its highly saturated main chain that leads to superior heat resistance, ozone resistance and weathering resistance.

This study aims to elaborate rubber profiles for autos windows and doors based on EPDM and EPDM/LLDPE blends formulations. The prepared rubber compounds and vulcaniztes of different formulations were evaluated by determining the rheometric characteristics and physico-mechanical properties. The rheometric and physico-mechanical tests reveal that:

The peroxide cure creates more crosslinks than sulfur cure.

Maleic anhydride plays a good role as compatibilizer for EPDM/LLDPE blend system.

The designed rubber profiles are characterized by good stability against heat and UV radiations.

All data will be discussed and the optimum formula would be recommended to rubber industry.

Keywords: Rubber, Blends, Physcio-mechanical properties, Auto-industry.

Introduction

Ethylene-propylene rubbers & elastomers (also called EPDM and EPM) continue to be one of the most widely used and fastest growing synthetic rubbers having both specialty and general-purpose applications. Versatility in polymer design and performance has resulted in broad usage in automotive weather-stripping and seals, glass-run channel, radiator, garden and appliance hose, tubing, belts, electrical insulation, roofing membrane, rubber mechanical goods, plastic impact modification, thermoplastic vulcanizates and motor oil additive applications.

Ethylene-propylene rubbers are valuable for their excellent resistance to heat, oxidation, ozone and weather aging due to their stable, saturated polymer backbone structure. Properly pigmented black and non-black compounds are color stable. As non-polar elastomers, they have good electrical resistivity, as well as resistance to polar solvents, such as water .

Thermoplastic elastomers are finding growing importance in fundamental research and practical applications. For instance, crosslinked polyolefin/ethylene-propylene-diene monomer (EPDM) blends are widely used as electrical insulating material, because of their excellent dielectric properties . The structural modification of such blends is generally achieved by incorporation of crosslinking agents (e.g. peroxide, sulfur). The dicumyl peroxide (DCP) crosslinking reaction of PE follows first-order kinetics, which is independent of peroxide concentration. The incorporation of heat stabilizers to LDPE and PP/EPDM blend systems effectively reduced the possible thermo oxidative degradation of the polymer components during their peroxide curing and extended their useful life .

These types of materials are commonly prepared by melting of thermoplastics with rubber using high shear stresses. For many applications the ideal plastic–rubber blend composes a structure formed with finely divided elastomer particles dispersed in a relatively small amount of plastic. Blends of polyolefins with partially crosslinked rubbers have been extensively investigated primarily with the aim of improving mechanical properties .

The present work aims at the study the rheological, physico-mechanical and chemical characteristics of EPDM/LLDPE blends crosslinked with sulpher/ accelerator and peroxide systems in the presence of MAH to elaborate rubber profiles for windows and doors. Also study the effect of thermal aging in air, at 90+1oC for different time intervals on the physic-mechanical and chemical properties. Also the work extended to study the effect of UV radiation on EPDM/LLDPE vulcanizates to elucidate the crack initiation

Experimental

Materials

Ethylene propylene diene monomer rubber (EPDM), with ethylene content of 55% and density of 0.86 g/cm3.

Zinc oxide (ZnO) with specific gravity at 15O C is 5.55 – 5.61.

Stearic acid whose specific gravity at 15O C is 0.9– 0.97.

Elemental sulfur with fine pale yellow powder and specific gravity of 2.04–2.06.

Dicumyl proxide (DCP), pure grade, melting point (39-41oC). Maleic anhydride, pure grade, M.wt. equal to 98.06 g/mol melting point 54-56 o C, Aldrich product.

High abrasion furnace (HAF) carbon black N-330 with the particle size of 40 nm and a specific gravity of 1.78-1.82.

N-cyclohexyl-2-benzothiazole sulfonamide (CBS) with specific gravity of 1.27–1.31 at room temperature 25 o C and melting point 95 o C –100 o C.

Polymerized 2, 2, 4-trimethyl-1,2dihydroquinoline (TMQ) was used as antioxidant.

Paraffin oil.

All these materials are supplied are kindly supplied from local rubber industry.

Linear low density polyethylene (LLDPE), obtained from SABIC, SA, with density 0.916 g/cm3.

Mixing procedure

EPDM was blended with LLDPE with different ratios in the brabender premixer at 160 oC for 10 min. at 60 r.p.m. Then the ingredients were added to the mix on a laboratory two-roll mill having an outside diameter of 470 mm and a working distance of 300 mm; speed of the slow roll was 24 rpm and the friction ratio was 1.4: 1. Table I shows the composition of the blends. The rheometric characteristics of the blends were studied using Monsanto Oscillating Disc Rheometer R-100. The composites were then press heated to produce molded sheets (2 mm thick) for physic-mechanical measurements.

Techniques of characterization

Rheometric and mechanical characteristics

The rheometric characteristics of the rubber compounds was determined using Monsanto Oscillating Disc Rheometer R-100 according to ASTM: D2084. The vulcanized sheets prepared for mechanical tests were cut into five individual dumb-bell shaped specimens by a steel die of constant width (4mm). The thickness of the test specimen was determined by a gauge calibrated in hundredths of a millimeter. A working part of scale 15 mm was chosen for each test specimen. The mechanical properties (e.g. tensile strength and elongation at break) of the rubber compounds were determined using electronic Zwick tensile testing machine, model 1425, in accordance with ASTM D 412.

Equilibrium swelling:

Equilibrium swelling test for the rubber compounds was conducted in toluene solvent for 24 h at room temperature 25 + 1oC according to the method described in standard test ASTM D3616.

Thermal aging:

Aging of samples was carried out at 90±1°C in air circulating oven for different time periods according to ASTM D 572-04, 2010. The reported results were averaged from a minimum of five specimens.

Ultra violet irradiation

AUV lamp of 254 nm wavelength and 7 MW/cm2 intensity was used as a source of irradiation.

Results and Discussions:

In the present work, blends of EPDM and thermoplastic materials such as LLDPE was prepared by melt mixing. This type of blend gives an overall material with good flexibility, whereas the thermoplastic regions contribute to the material’s overall strength. The varying percentage of EPDM and thermoplastics can lead to materials with a wide variety of interested properties. Table 1 gives the formulations, the rheometric characteristics and physico-mechanical properties such as stress at rupture (σR), elongation at break (εR), equilibrium swelling (Q) of pure EPDM as well as two different blend compositions of EPDM with LLDPE thermoplastic in 75/25 and 50/50 w/w%.

These two blends were selected to be crosslinked with different crosslinking agents and namely with peroxide and sulphur/accelerator systems.

From the data in Table (1), one can see that the stress at rupture of the pure EPDM sample with sulphur/accelerator systems more little than peroxide. On the other hand the elongation at break of the vulcanized rubber with sulphur/accelerator systems was decreased slightly.

It was noticed that the stress at rupture and elongation at break values were improved with peroxide content and have higher values compared with S/CBS system (Table 1). This can be attributed to the fact that peroxide can crosslink both EPDM and LLDPE phases, but S/CBS system crosslink only the EPDM phase in the blend .

The data in Table 1 indicate that pure EPDM rubber possesses recoverable high elasticity, because the medium and higher values of propylene content (i.e.,41–44% in EPDM structure) will produce softer and more elastic polymers .

It has been also noticed that the tensile strength of 50:50 blend ratio is higher than that for 25:75 blend ratio. The only way to explain this behavior may be attributed to ability of peroxide to crosslink LLDPE more than EPDM .

The data in Table 1 also show that EPDM rubber gives the highest values of equilibrium swelling as compare3d with other types of blends. This can be attributed to chain bonds and physical forces in each molecule. It can be expected that equilibrium swelling of a plastic material decreases by adding LLDPE. Thus increasing EPDM content in the blend 75% shows an increase in the equilibrium swelling as compared with 50% EPDM contents.

On the other hand the equilibrium swelling of the vulcanized rubber was decreased due to the crosslinking of EPDM gum in the blend. As the crosslinking process started and the EPDM chains were connected with each other via chemical bonds, the elongation was decreased, while the stress at rupture was increased. This is based on the fact that S/CBS system crosslinks only the EPDM phase in the blend however, peroxide can crosslink both EPDM and LLDPE phases. This is clearly seen from the data in table (1) for the EPDM/LLDPE blend 25/75 and 50/50, where the EPDM content was increased and LLDPE decreased.

Aging of rubber blends

It is worthy to study the effect of curing system on the aging characteristics of EPDM/LLDPE blend. For this task the rubber vulcanizates were subjected to thermal aging in an oven with good air circulation at the temperature 90 °C for 120 hrs. The physico-mechanical properties of the aged samples were determined according to ASTM standards and listed in Table (1). It is worthy to notice that, the rubber blend samples containing peroxide have the greatest efficiency to resist aging.

The stress at rupture and elongation at break for EPDM/ LLDPE blend 75/25, and 50/50 give higher value for resistance aging compared with pure EPDM.

The effect of maleic anhydride (MAH) on the EPDM/LLDPE blends:

To improve the miscibility of EPDM/LLDPE blends, maleic anhydride was introduced in the blends during mixing . The (MAH) reacts with LLDPE and modify it.Consequently the maleated LLDPE can be play the role of good compatibilizer.

The physico-mechanical properties were determined and the results are given in Table (2). The data obtained reveal that the improvement of the physico-mechanical properties is due to the enhancement of the miscibility of the blends under investigation .

UV light ageing:

The vulcanizates of formulations A1, A3, A7, A4, A8, A9, A5, and A6 were subjected to the UV irradiation for 90 days. Figs (1, 2) demonstrate the blends before radiation and Figs (2 , 4) show the same blends after irradiation. One can see that the rubber compounds generated according to these formulations have showed no signs of cracks have been detected after radiation for long time. This can be attributed to the deficiency of unstauration of the blends and the good compatibilization of maleic anhydride.

CONCLUSIONS

The peroxide curing system crosslinks both EPDM and LLDPE and slightly improved the physico-mechanical properties of EPDM/LLDPE blend.

The use of maleic anhydride improves the physico-mechanical properties and plays the role of blend modifier.

The investigated blends showed excellent stability to UV radiation and can be recommended for the production of different profiles for auto-industry.

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