The Tribologic and Thermomechanic Properties of Polypropylene Filled with CaCO 3 and Anhydrous Borax

Transcription

1 The Tribologic and Thermomechanic Properties of Polypropylene Filled with CaCO 3 and Anhydrous Borax EROL FEYZULLAHOG LU* AND TU LIN SAHIN Department of Mechanical Engineering, Kocaeli University, Kocaeli, Turkey ABSTRACT: There are few studies showing the industrial application of boron compounds. In this study, boron compounds are used as fillers in plastic materials in order to increase the use of these raw materials. The effect of anhydrous borax mineral in the thermomechanical and tribologic properties of both calcium carbonate (CaCO 3 ) unfilled and CaCO 3 filled polypropylene (PP) material is investigated. Wear and thermomechanical properties of specialized PP material containing additives are examined by using pin-on disc wear tester, DSC, TMA and Shore D hardness testers. This study is the first to use boron (anhydrous borax) compounds as an additive in industrial plastics. As a consequence of the increase in the amount of boron in the samples, the friction coefficient also increases. An increase in the amount of CaCO 3 used as an additive in the samples containing the same percentage of boron reduces the friction coefficient. Using anhydrous borax and CaCO 3 as additives in a natural PP material did not create a considerable change in the crystalline melting temperature of the material. Weight loss increases for anhydrous borax, while it decreases for CaCO 3 compared with natural PPB. If the amount of anhydrous borax is increased, the weight loss increases too. The minimum weight loss is seen for % CaCO 3. This increases with an increasing amount of CaCO 3 and is close to natural PPB. KEY WORDS: tribology, thermomechanical properties, polypropylene, anhydrous borax, CaCO 3. INTRODUCTION POLYPROPYLENE (PP) IS an industrial plastic, which has a wide usage in industry due to its easy workability, high strength, and high wear resistance [1,2]. The wear resistance of PP is lower than that of other engineering plastics, such as high density polyethylene and nylon [3]. The tribologic and wear behaviors of plastic materials are all important within machine elements, such as gears, journal bearings, and sledges. Tribologic behaviors of PP, which is a thermoplastic material, differ from that of metals. Thermoplastics have lower static friction coefficient than dynamic friction coefficient. This gives the feature of sliding/adhesion or discontinuous sliding behavior to the thermoplastics working together with other metal or plastics [4]. The increase of friction and wear depends on the surface energy. When the load arises a limit value, this increase occurs. Increase of temperature on the contact surfaces causes the molecule chains of polymer to relax [5]. *Author to whom correspondence should be addressed. efeyz@kocaeli.edu.tr Journal of REINFORCED PLASTICS AND COMPOSITES, Vol. 29, No. 16/ // $.00/0 DOI:.1177/ ß The Author(s),. Reprints and permissions:

2 Properties of Filled Polypropylene 2499 The wear of UHMWPE is dependent on the surface temperature. When the temperature exceeds a critical value, wear proceeds in a series of discrete steps caused by the sudden loss of a molten or softened layer of polymer [6]. When friction coefficient is lower, less friction heat will be produced; therefore the surface temperature will be lower, which indicates better anti-wear properties [7]. The end product costs and product quality are improved by adding mineral additives, such as calcium carbonate (CaCO 3 ), talc, and barium sulfate (BaSO 4 )to PP materials. It is known that PP material affects all physical and mechanical properties as well as the amount of the filler other than its type [8]. Sole and Ball investigated the effects of mineral fillers on the wear resistance of PP. They used talc, CaCO 3, and BaSO 4 as mineral fillers. The addition of mineral fillers to the PP decreases the wear resistance under severe abrasive conditions [9]. The mechanical and thermal properties of polymers can be greatly improved by the addition of inorganic additives. The PPs with different additives are widely used to make packing and architectural material, because of their high strength/density ratio. The strength of PP can be enhanced by filling with CaCO 3 particles []. Numerous studies have been performed on the wear properties of PP composites by considering the traditional fillers, such as non-ferrous metallic powders, kaolin, and some oxides. The kaolin fillers improve tensile strength of polymer materials [11]. It is widely known that the tribologic behaviors of polymers can sometimes be greatly improved by filling them with inorganic particulate compounds. Kaolin filled at certain content is effective to reduce friction and wear of polymer materials in sliding against steel [12]. Addition of kaolin particulates to PTFE causes an increase in wear resistance [13]. Nedorezova and Tsvetkova investigated the properties of PP filled boron nitride. In their study, the strength of materials is increased and friction properties are improved [14]. Nowadays, industrial application of studies as-built with boron compounds is considerably low. In this study, boron compounds are used as filler in plastic materials in order to increase the use of these raw materials. In literature, there are very few studies regarding the use of boron compounds as an additive in plastic materials. The effect of anhydrous borax mineral on the thermomechanical and tribologic properties of both CaCO 3 unfilled and CaCO 3 filled PP material was investigated. Wear and thermomechanical properties of specialized PP material containing additives are examined by using pin on disc wear tester, DSC, TMA, and Shore D hardness testers. This study is considered as a new one, which uses boron (anhydrous borax) compounds as additive in industrial plastics. Material EXPERIMENTAL STUDY In this study, polypropylene block copolymer (PPB) produced in BEC15 trade name of Borealis and in its natural color and granular state is used as a basic polymer material ( The important physical and mechanical properties of samples which are produced with the injection molding method are shown in Table 1. CaCO 3 mineral filler, which is produced as granulated in Imercab-2XG trade name by Mikromineral, is preferred when obtaining mineral filled PPB raw materials ( The basic characteristics of CaCO 3 mineral filler are presented in Table 2. In this study, green anhydrous borax mineral is used by pulverizing it to a mean particle diameter of 5 mm.

3 20 E. FEYZULLAHOG LU AND T. SAHIN Table 1. The physical and mechanical properties of PPB. Properties Test method Test conditions Unit system BEC15 natural Tensile yield stress ISO mm/min MPa Tensile yield strain ISO mm/min % Tensile modulus of elasticity ISO mm/min MPa Charpy impact (notched) ISO 179/1eU +23 C kj/m 2 70 Charpy impact (notched) ISO 179/1eU C kj/m 2 7 Hardness ISO 39-2 Rockwell-R scale 72 Melt flow index ISO C / 2.16 kg g/ min 0.3 Density ISO1183 g/cm Table 2. Basic characteristics for CaCO 3 mineral filler. Properties Test method Test conditions Unit system Mineral material CaCO 3 ratio % Mean particle diameter (D %) mm 2.15 Maximum particle diameter (D 97%) mm 11.6 Density ISO787/ g/cm Brightness DIN Ry, C/2 % Table 3. Anhydrous borax _ CaCO3 mixing list. By volume CaCO 3 By weight anhydrous borax 0% 0% 0.5% 1% 2% % 0% 0.5% 1% 2% 15 % 0% 0.5% 1% 2% % 0% 0.5% 1% 2% Preparation of Samples Double driven screw extrusion, which turns parallel to each other, was used when producing the samples. Samples were prepared by adding CaCO 3 in %, 15%, and % by volume (25%, 34.62%, and 42.86% by weight) and anhydrous borax mineral filler in 0.5%, 1%, and 2% by weight to PP materials when extruding as shown in Table 3. Arburg Allrounder 370 CMD model injection machine was used to prepare the samples.

4 Properties of Filled Polypropylene 21 Load Sample clip Sample Sample Steel disc Figure 1. Pin on disc wear test. Wear Experiments The samples with a mm 3 dimension were prepared for wear tests. TE 53 Slim model pin-on disc wear testing machine was used for analysis of friction and wear behaviors of test samples (Figure 1). The wear tests were performed with 5 N load and 1.57 m/s sliding speed in accordance with ISO The disc of wear testing device had a diameter of 60 mm and was produced of 95 HRB hardness SAE 40 steel. Wear values were obtained as weight loss (mg) at the end of 4 h. Wear rates and friction coefficients were calculated. In wear tests, km sliding distance was achieved at the end of 4 h. In wear tests, weights of samples were measured with Precisa 125 A precision balance. The balance has g precision. Tests were carried out in 22 C and in a % RH. Wear rate was estimated by the formula [7]: W s ¼ W L where W s is the wear rate (cm 3 /m), W is the weight loss (g), q is the density (g/cm 3 ) q = 0.9 g/cm 3 (density of PP), L is the sliding distance (m). DSC Experiments Weight samples of mg were prepared from each test group. Differential scanning calorimeter (DSC) test was started at 25 C and terminated at 2 C with a heating rate of C/min and nitrogen was used as the inert gas according to ISO 3146 standard.

5 22 E. FEYZULLAHOG LU AND T. SAHIN 65 Weight loss (mg) % Natural 0.5% Anhydrous borax 1% Anhydrous borax 2% Anhydrous borax % CaCO 3 15% CaCO 3 % CaCO 3 Figure 2. The sliding distance weight loss relationship in natural PP materials mixed with anhydrous borax. Crystalline melting temperatures of samples and crystallizing degrees were determined in percentages (% c) by using the test equipment trademark of Metller Toledo DSC1. TMA Experiments Samples of dimensions 6 6 3mm 3 were analyzed by heating from 25 C to 170 Cata rate of 5 C/min and using 0.5 gram weight in thermomechanical analyzer (TMA) test. The coefficient of thermal expansion (a) and the glass transition temperatures (T g )ofthe samples were acquired using a thermomechanical analyzer trademark of TMA- Shimadzu in ASTM D 1545 and ASTM E 1363 standards. Shore D Experiments Shore D hardness tests of the samples were carried out using Zwick 30 Type D hardness tester according to ISO 868 standard. SEM Examinations Wear surfaces of the samples resulting from wear test were examined with a SEM tester trademark of Jeol Wear Results The relationship between sliding distance and weight loss in natural PP materials mixed with anhydrous borax and CaCO 3 is shown in Figure 2. As the sliding distance increases,

6 Properties of Filled Polypropylene 23 weight loss also increases. As the amount of anhydrous borax additive in samples increases, more wear is seen in the samples along with the sliding distance. The effects of anhydrous borax and CaCO 3 on the tribological properties of PPB are different. The weight loss increases for anhydrous borax while it decreases for CaCO 3 compared with that of natural PPB. The reduction of wear as per natural material is seen in the case of adding anhydrous borax and CaCO 3 into the PP material. In Figure 3, it can be seen that using % CaCO 3 as an additive in PP material in comparison with natural material creates serious reduction in weight losses. In case of using anhydrous borax as an additive in samples contain 15% CaCO 3 a little rise in weight losses appears (Figure 4). The samples containing % CaCO 3 as an additive and several amounts of anhydrous borax were worn out less compared to the samples which are natural and contain only % CaCO 3. Increase in CaCO 3 percentage and samples containing anhydrous borax create serious reductions in weight losses of samples (Figure 5). Figure 6 shows that increase in the amount of anhydrous borax in the samples containing 0% CaCO 3 also increases the wear rate. It is also seen that using anhydrous borax as an additive in material containing % and 15% CaCO 3 increases the wear rate in a considerable level. In consequence of the availability of both fillers, the wear rate was significantly lower than that of natural material (Figures 7, 8). When Figures 7 and 8 were reviewed together, it was seen that the increase in the amount of CaCO 3 also increases the wear rate values generally. The wear rates of the PP material containing anhydrous borax mixed with % CaCO 3 are presented in Figure Natural % CaCO 3 0.5% Anhydrous borax+% CaCO 3 1% Anhydrous borax+% CaCO 3 2% Anhydrous borax+% CaCO 3 Weight loss (mg) Figure 3. The sliding distance weight loss relationship in PP materials containing anhydrous borax mixed with % CaCO 3.

7 24 E. FEYZULLAHOG LU AND T. SAHIN Weight loss (mg) Natural 15% CaCO 3 0.5% Anhydrous borax+15% CaCO 3 1% Anhydrous borax+15% CaCO 3 2% Anhydrous borax+15% CaCO 3 15 Figure 4. The sliding distance weight loss relationship in a PP material containing anhydrous borax mixed with 15% CaCO 3. Weight loss (mg) Natural % CaCO 3 0.5% Anhydrous borax+% CaCO 3 1% Anhydrous borax+% CaCO 3 2% Anhydrous borax+% CaCO 3 Figure 5. The sliding distance weight loss relationship in a PP material containing anhydrous borax mixed % CaCO 3.

8 Properties of Filled Polypropylene % CaCO 3 31 Wear rate (W s 7 ) (cm 3 /m) % Anhydrous borax 0.5% Anhydrous borax 1% Anhydrous borax 2% Anhydrous borax Figure 6. The sliding distance wear rate relationship in a natural PP material mixed with anhydrous borax (0% CaCO 3 ). 27 Wear rate (W s 7 ) (cm 3 /m) Natural % CaCO 3 0.5% Anhydrous borax+% CaCO 3 1% Anhydrous borax+% CaCO 3 2% Anhydrous borax+% CaCO 3 9 Figure 7. The sliding distance wear rate relationship in a PP material contains anhydrous borax mixed with % CaCO 3.

9 26 E. FEYZULLAHOG LU AND T. SAHIN Wear rate (W s 7 ) (cm 3 /m) Natural 15% CaCO 3 0.5% Anhydrous borax+15% CaCO 3 1% Anhydrous borax+15% CaCO 3 2% Anhydrous borax+15% CaCO 3 17 Figure 8. The sliding distance wear rate relationship in a PP material containing anhydrous borax mixed with 15% CaCO 3. Wear rate (W s 7 ) (cm 3 /m) Natural % CaCO 3 0.5% Anhydrous borax+% CaCO 3 1% Anhydrous borax+% CaCO 3 2% Anhydrous borax+% CaCO 3 Figure 9. The sliding distance wear rate in the PP material containing anhydrous borax mixed with % CaCO 3.

10 Properties of Filled Polypropylene Friction coefficient Anhydrous borax (%) 0% CaCO 3 % CaCO 3 % CaCO 3 2 Figure. The relationship between the amount of anhydrous borax and the friction coefficient in the samples. The values of the samples containing high percentages of CaCO 3 are close to the values of natural materials. As the amount of anhydrous borax in the samples containing anhydrous borax increases, the wear rate also increases. As a consequence of the increase in the amount of anhydrous borax in the samples, the friction coefficient also increases. In the samples containing anhydrous borax in the same percentages, the increase in CaCO 3 that was used as an additive reduces the friction coefficient (Figure ). DSC Results Figure 11 shows that using CaCO 3 as an additive in the natural material reduces the crystallizing degree of the material. Using additives such as anhydrous borax and CaCO 3 in the PP material as shown in Figure 12 did not create a remarkable variation in crystalline melting temperature of the samples. Since using additives does not affect the crystalline melting temperature, the resultant temperature increase also does not affect the physical properties of the material. During wear, the temperature of the contact area increases, the bond structure of the material impairs, and as a result of these the dissociations occur in the material [15]. Reaching high melting temperatures enhances the thermal stability. In this study, acquired DSC results demonstrate the validity of this stability [1]. TMA Results Figure 13 shows that no considerable changes have occurred to the T g of the samples containing anhydrous borax mixed with CaCO 3 depending on the percentage of boron.

11 28 E. FEYZULLAHOG LU AND T. SAHIN Crystallizing degree (J/G) (%) % CaCO 3 (Natural) % CaCO 3 15% CaCO 3 % CaCO Anhydrous borax (%) Figure 11. Anhydrous borax crystallizing degree relationship in the PP material containing anhydrous borax and CaCO % CaCO 3 (Natural) 8 Crystalline melting temperature ( C) (%) % CaCO 3 15% CaCO 3 % CaCO Anhydrous borax (%) 2 0 Figure 12. Anhydrous borax crystalline melting temperature relationship in the PP material containing anhydrous borax and CaCO 3.

12 Properties of Filled Polypropylene Glass transition temperature (T g ) % CaCO 3 % CaCO 3 15% CaCO 3 % CaCO Anhydrous borax (%) 2 Figure 13. Glass transition temperature change depending on the amount of anhydrous borax mixed with CaCO 3. In Figure 14, as the amount of anhydrous borax increases, a considerable decrease occurs in the coefficient of thermal expansion of the sample unfilled with CaCO 3. The thermal expansion coefficient has been increased depending on the percentage of the boron in the sample mixed with 15% CaCO 3 (Figure 14). Hardness Results The change in shore D hardness values in the PP samples containing CaCO 3 depending on the anhydrous borax amount used as an additive over natural samples are given in percentages in Figure 15. In the examination, it was seen that the shore D hardness reduces in case of adding anhydrous borax in natural PP, the shore D hardness increases in PP mixed with CaCO 3 depending on the CaCO 3 amount (Figure 15). SEM Results The scanning electron micrographs under conditions for same load and same sliding distance of both unmixed and mixed samples are shown in Figures 16 and 17. On the wear surfaces of natural samples, more evident breakings are seen than in the mixed samples. Re-breakings on the wear surfaces with more than % CaCO 3 filler are also shown in Figure 16(c). However, these breakings are not seen on the wear surface of the sample containing 2% anhydrous borax as an additive due to good adhesion. No evident dissociations are seen

13 25 E. FEYZULLAHOG LU AND T. SAHIN Thermal expansion coefficient ( 6 / C ) PPB PPB+15% CaCO 3 +Anhydrous borax Anhydrous borax (%) 2 Figure 14. The thermal expansion coefficient depending on the boron amount of the natural PP material containing anhydrous borax filled with CaCO % CaCO 3 75 % CaCO 3 15% CaCO 3 70 % CaCO 3 Shore D hardness Anhydrous borax (%) 2 Figure 15. The shore D hardness anhydrous borax amount relationship in the PP material mixed with CaCO 3.

14 Properties of Filled Polypropylene 2511 Figure 16. The scanning electron micrographs of the wear surfaces of the natural and mixed with CaCO 3 samples: (a) 0% C a CO 3, (b) % C a CO 3, and (c) 15% C a CO 3. Figure 17. The scanning electron micrographs of the wear surfaces of the samples containing anhydrous borax and CaCO 3 : (a) 2% anhydrous borax, (b) % C a CO 3 and 2% anhydrous borax, and (c) 15% C a CO 3 and 2% anhydrous borax. according to the natural materials as shown in Figure 17(b) and (c) due to the effect of adding both anhydrous borax and CaCO 3 filler. CONCLUSIONS (1) The effects of anhydrous borax and CaCO 3 on the tribological properties of PPB are different. The weight loss is increased for anhydrous borax while it is decreased for CaCO 3 compared with natural PPB. If the amount of anhydrous borax is increased, the weight loss is increased too. The minimum weight loss is seen for % CaCO 3.Itis increased with increasing the amount of CaCO 3 and closed to natural PPB. (2) As the amount of boron in the samples containing only anhydrous borax increases, the wear rate also increases. The increase in the amount of CaCO 3 also increases the wear rate values generally. (3) As a consequence of increase in boron amount in the samples, the friction coefficient also increases. Increase in the amount of CaCO 3 used as an additive in the samples containing the same percentage of boron reduces the friction coefficient. (4) Using anhydrous borax and CaCO 3 as an additive in a natural PP material does not create considerable change in the crystalline melting temperature of the material. (5) There has been no considerable change in the T g of the samples containing anhydrous borax mixed with CaCO 3. (6) As the amount of anhydrous borax increases, considerable change in the thermal expansion coefficient of the sample unfilled with CaCO 3 is seen. An increase is seen in the thermal expansion coefficient depending on the boron percentage in case of the sample mixed with 15% CaCO 3.

15 2512 E. FEYZULLAHOG LU AND T. SAHIN (7) In case of adding anhydrous borax in the PP material unmixed with CaCO 3,itis determined that the shore D hardness decreases; in case of PP material mixed with CaCO 3 depending on the CaCO 3 amount, the shore D hardness increases. (8) When the scanning electron micrographs of the wear surfaces of natural samples were investigated, more breakings were observed than in the mixed materials. However, these breakings on the wear surface of the sample containing 2% anhydrous borax as an additive are seen due to being a good adhesion on the surface of the sample. REFERENCES 1. Chand, N. and Dwivedi, U. K. (06). Effect of Coupling Agent on Abrasive Wear Behaviour of Chopped Jute Fibre Reinforced Polypropylene Composites, Wear, 261: Menges, G. (1998). Werkstoffkunde Kunststoffe, Carl Hanser Verlag, Mu nchen. 3. Chand, N. and Naik, A. (07). Abrasive Wear Studies on Maleic Anhydride Modified Polypropylene and Polyethylene Terephthalate Blends, Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 221: Blase, C. (1991). Plastic Bearings Carry Heavier Load, Machine Design, 24: Unal, H. and Mimaroglu, A. (03). Friction and Wear Behaviour of Unfilled Engineering Thermoplastics, Materials and Design, 24: Barrett, T. S., Stachowiak, G. W. and Batchelor, A. W. (1992). Effect of Roughness and Sliding Speed on the Wear Friction of Ultra-high Molecular Weight Polyethylene, Wear, 153: Liu, G., Chen, Y. and Li, H. (04). A Study on Sliding Wear Mechanism of Ultrahigh Molecular Weight Polyethylene/Polypropylene Blends, Wear, 256: Leong, Y. W., Abu Bakar, M. B., Mohdishak, Z. A., Ariffin, A. and Pukanszky, B. (04). Comparison of the Mechanical Properties and Interfacial Interactions between Talc, Kaolin, and Calcium Carbonate Filled Polypropylene Composites, Journal of Applied Polymer Science, 91: Sole, B. M. and Ball, A. (1996). On the Abrasive Wear Behaviour of Mineral Filled Polypropylene, Tribology International, 29: Li, Y., Fang, Q. F., Yi, Z. G. and Zheng, K. (04). Study of Internal Friction in Polypropylene (PP) Filled with Nanometer-scale CaCO 3 Particles, Materials Science and Engineering A, 370: Buggy, M., Bradley, G. and Sullivan, A. (05). Polymer-filler Interactions in Kaolin/Nylon 6.6 Composites Containing a Silane Coupling Agent, Composites. Part A, Applied science and manufacturing. S, 36: Guofang, G., Huayong, Y. and Xin, F. (04). Tribological Properties of Kaolin Filled UHMWPE Composites in Unlubricated Sliding, Wear, 256: Xiang, D. and Gu, C. (06). A Study on the Friction and Wear Behavior of PTFE Filled with Ultra-fine Kaolin Particulates, Materials Letters, 60: Nedorezova, P. M. and Tsvetkova, V. I. (1997). The Effect of the Dispersion of Graphite and Boron Nitride on the Properties of Polymerization-filled Compositions Based on Polypropylene, Vysokomolekulyarnye Soedineniya A&B, 39: Chand, N., Majumdar, B. and Fahim, M. (1994). Theory of Abrasive Wear Mechanism for FRP Composite, Indian Journal of Engineering and Materials Sciences, 1: