- Email: [email protected]
Recycling of irradiated high-density polyethylene
Radiation Physics and Chemistry 106 (2015) 68–72
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Recycling of irradiated high-density polyethylene J. Navratil a,n, M. Manas a,1, A. Mizera a,2, M. Bednarik a,3, M. Stanek a,4, M. Danek b,5 a b
Tomas Bata University in Zlin, nam. T.G. Masaryka 5555, 760 01 Zlin, Czech Republic BGS Beta-Gamma-Service GmbH & Co. KG, Masarykova 378, 696 02 Straznice, Czech Republic
H I G H L I G H T S
Utilization of recycled irradiated material as a filler is proposed. LDPE/HDPEx mixtures were prepared in six concentrations. Processability and mechanical behavior were investigated and compared. Possible utilization of irradiated material after the end of its lifetime was proven.
art ic l e i nf o
a b s t r a c t
Article history: Received 5 March 2014 Accepted 29 June 2014 Available online 7 July 2014
Radiation crosslinking of high-density polyethylene (HDPE) is a well-recognized modification of improving basic material characteristics. This research paper deals with the utilization of electron beam irradiated HDPE (HDPEx) after the end of its lifetime. Powder of recycled HDPEx (irradiation dose 165 kGy) was used as a filler into powder of virgin low-density polyethylene (LDPE) in concentrations ranging from 10% to 60%. The effect of the filler on processability and mechanical behavior of the resulting mixtures was investigated. The results indicate that the processability, as well as mechanical behavior, highly depends on the amount of the filler. Melt flow index dropped from 13.7 to 0.8 g/10 min comparing the lowest and the highest concentration; however, the higher shear rate the lower difference between each concentration. Toughness and hardness, on the other hand, grew with increasing addition of the recycled HDPEx. Elastic modulus increased from 254 to 450 MPa and material hardness increased from 53 to 59 ShD. These results indicate resolving the problem of further recycling of irradiated polymer materials while taking advantage of the improved mechanical properties. & 2014 Elsevier Ltd. All rights reserved.
Keywords: Irradiation Radiation crosslinking Recycling High-density polyethylene Filler
1. Introduction The growing knowledge of properties' change of polymers after irradiation has led to an increasing usage of cheap, commodity plastics in the areas where it was unthinkable before. Several investigations of why there is such a boost in the spread of this technology have been done and it has been found that there are several reactions of exposed polymer materials including crosslinking, degradation and grafting (Cheng et al., 2010; Cheremisinoff, 1998). n
Corresponding author. Tel.: þ 420 576035152; fax: þ 420 576035176. E-mail addresses: [email protected] (J. Navratil), [email protected] (M. Manas), [email protected] (A. Mizera), [email protected] (M. Bednarik), [email protected] (M. Stanek), [email protected] (M. Danek). 1 Tel.: þ420 576035630; fax: þ 420 576035176. 2 Tel.: þ420 576035226; fax: þ 420 576035176. 3 Tel.: þ420 576035226; fax: þ 420 576035176. 4 Tel.: þ420 576035153; fax: þ420 576035176. 5 Tel/fax: þ 420 518324510. http://dx.doi.org/10.1016/j.radphyschem.2014.06.025 0969-806X/& 2014 Elsevier Ltd. All rights reserved.
Crosslinking is the most desirable reaction in order to enhance physical properties such as chemical resistance, mechanical behavior and thermal stability. Radiation crosslinking can be applied to thermoplastics, elastomers and thermoplastic elastomers (Rouif, 2005). Polyethylenes belong among one of the most radiation crosslinked materials. They crosslink without need of any crosslinking additive and they can be easily tailored to suit specific application (Rouif, 2005; Gehring, 2000). Three-dimensional polymer network is created in the crosslinked structure through branching of individual chains (Bhattacharya, 2000). Despite properties improvement, radiation crosslinked thermoplastic materials are losing their natural ability of being remelted repeteadly due to the network formation. This raises the issue of further waste processing. All previous research papers dealt with irradiation of recycled materials (Burrilo et al., 2002; Adem et al., 1998) but none of them dealt with recycling of the irradiated materials. This research paper offers a solution to this problem and it suggests an answer to it.
J. Navratil et al. / Radiation Physics and Chemistry 106 (2015) 68–72
2. Experimental part 2.1. Materials Low-density polyethylene (LDPE) was chosen as the polymer matrix regarding its good processability, low price and good availability. The commercial LDPE was supplied by The Dow Chemical Company - LDPE 780E. The melt flow index (MFI) measured according to the ISO 1133 standard at 2.16 kg load and 190 1C is 20 g/10 min. High-density polyethylene (HDPE) was chosen due to its wide spread in radiation industry and thus a great potential of being recycled, despite problematic miscibility with LDPE (Fan et al., 2002; Nwabunma and Kyu, 2008). This material was supplied in the form of irradiated floor heating pipes. Exact HDPE type used for their manufacturing was not determined; but, comparable “piping” HDPE type was used for comparison purposes. This material was supplied by Slovnaft Petrochemicals – HDPE Tipelin PS 380-30/302. The MFI measured according to the ISO 1133 standard at 5 kg load and 190 1C is 0.95 g/10 min.
2.1.1. Radiation processing Irradiation of these pipes was originally carried out at the BGS Beta–Gamma–Service company. Electron beam radiation was used for their irradiation, the dose was 165 kGy and the energy was 10 MeV, both parameters were set according to the HDPE manufacturer's recommendation. Dynamic method where rotating pipe (3601) is irradiated under the beam (irradiation direction was from the scanner from top quick vertical and in to the cross direction) on the conveyor was used to provide homogenous and uniform dose distribution. The required dose is determined according to the accelerator parameters (voltage, current, speed and amount of the windings of the conveyor) and its correctness is measured by gel content and by dosimeter. Nylon FWT 60-00 dosimeter was used to check the correct radiation dose, following analysis was carried out on spectrophotometer genesis 5 (calibration was according to the ASTM 51261 standard). Gel content of this material was measured according to the ASTM D7567 standard where it is determined by solvent extraction with xylene. Results shown that dose 165 kGy corresponds to 60% gel content.
69
2.2.1. Melt flow index Dynisco Kayeness LMI 4003 melt flow indexer was used for the MFI measurement of the proposed mixtures. Measurement was carried out in accordance with ISO 1133 standard at 2.16 kg load and 190 1C. 2.2.2. Polymer fluidity Testing laboratory injection mold with spiral cavity was used for the polymer fluidity determination. Length of the resulting spiral is up to 2 m and the cross-section shape is rectangular 6 1 mm2 (Fig. 2). Testing was done on the injection molding machine Arburg Allrounder 420C. 2.2.3. Flow curves Flow curves measurement was carried out on capillary rheometer Goettfert Rheograph 2001. Capillary L/D ratio was 20/1, testing temperature was 190 1C and shear rate range was from 35 to 2500 s 1. 2.2.4. Tensile test Tensile testing machine ZWICK 1456 was used for the tensile behavior estimation. Measurement was carried out according to the ISO 527 standard at ambient conditions. A crosshead speed of 50 mm/min was used throughout the whole measurement. E-modulus and ultimate tensile strength were evaluated from this measurement. 2.2.5. Shore D hardness OMAG AFFRI ART 13 Shore D hardness tester was used for hardness testing in accordance with ISO 868 standard. Hardness was measured on the same specimen as tensile behavior (Fig. 3). Measurement of all above mentioned properties was performed 15 times to ensure statistical correctness. 2.2.6. Structural analysis LEICA RM2255 microtome was used for the sample's preparation (thickness 35 mm) and microscope Olympus BX41 was utilized for the structural analysis.
3. Results and discussion 3.1. Processability
2.2. Methods Powder/powder mixtures of these materials were used in this investigation. Therefore recycled irradiated pipes were ground into a powder. Cleaned, chopped pipes were first crushed into the particles of 5 mm main size (Fig. 1) and then ground into the particles of 500 μm main size. LDPE powder was used as the polymer matrix and HDPEx powder was used as the filler. Materials were mixed in concentrations from 10% to 60%. Mixing was carried out in the laboratory fluid mixer for 5 min.
Fig. 1. Crushed pipes from recycled HDPEx.
Processing of the filled materials is a problematic operation and many factors have to be taken into account. For example the
Fig. 2. Spiral cavity plate and testing sample.
70
J. Navratil et al. / Radiation Physics and Chemistry 106 (2015) 68–72
Fig. 3. Melt flow index comparison.
Fig. 6. Resulting spirals: a) LDPE þ10% HDPEx, b) LDPE.
10000
LDPE LDPE+10% HDPEx
Shear viscosity [Pa.s]
LDPE+30% HDPEx LDPE+60% HDPEx
1000
HDPE
100
10
10
100
1000
10000
Shear rate [s-1]
Fig. 7. Elastic modulus comparison.
Fig. 4. Flow curves comparison.
Fig. 8. Material strength comparison.
Fig. 5. Polymer fluidity comparison.
viscosity increase/decrease depends on the properties of the filler, on the size of the filler etc. (Wypych, 2010). Melt flow index determination is a standard test of polymer flow behavior. Effect of the recycled HDPEx filler on the MFI is shown in Fig. 3. It can be seen that there is a substantial MFI decrease comparing the virgin LDPE and LDPEþ 10% HDPEx. Further addition of the filler results in a gradual decrease of the MFI. Overall drop is 96% comparing LDPE and LDPE mixed with the highest concentration of the recycled HDPEx. The MFI determines flow behavior only at low shear rates and thus higher shear rates have to be taken into account to fully describe the processing behavior. Flow curves were measured at shear rate up to 2500 s 1. In Fig. 4 flow curves of the three
Fig. 9. Material hardness comparison.
J. Navratil et al. / Radiation Physics and Chemistry 106 (2015) 68–72
71
Fig. 10. Resulting spirals: a) LDPE, b) LDPE þ 10% HDPEx, c) LDPE þ 30% HDPEx, d) LDPE þ 60% HDPEx.
different filling concentrations compared with the virgin LDPE and HDPE are depicted. It can be seen that the differences between each mixture are much higher at lower shear rates than at higher
shear rates where the differences are almost negligible. This result is in correlation with the statement that within the range of shear stress of 105–106 Pa (which is best suited for material processing)
72
J. Navratil et al. / Radiation Physics and Chemistry 106 (2015) 68–72
viscosity does not increase as rapidly (Wypych, 2010). The HDPE shows almost identical behavior to the LDPE with 30% of recycled HDPEx. The observed gap between the LDPE and the filled LDPEs remained unchanged even at higher concentrations. The spiral fluidity test simulates the real processing conditions the most closely. A huge drop of the polymer fluidity can be seen in Fig. 5 comparing the LDPE and the LDPE with 10% of the recycled HDPEx, this corresponds with the previously achieved results. Further increase of the filler negatively influenced the fluidity only gradually. Length of the spiral decreased from 50.5 mm to 20 mm comparing the filled LDPEs. The worst result was achieved at the virgin HDPE where the length was only 18 mm. In Fig. 6 resulting spirals are compared and where a significant difference between the filled and the virgin LDPE can be seen. It can be observed that the processability is strongly influenced by the filler. Even the lowest concentration of the recycled HDPEx caused a significant drop in the processability. It can be seen that the differences between filled LDPEs are very small. 3.2. Mechanical properties Dumb-bell shaped specimens with 10 4 30 (width thickness length) measurement area's dimensions were used for the investigation. Testing specimens were injection molded using the Arburg Allrounder 420C injection molding machine. Toughness of the resulting mixtures represented by the E-modulus is shown in Fig. 7. E-modulus grown constantly with the increasing amount of the filler. Despite big drop in the processability of the filled LDPEs the toughness growth is only steady. However the overall increase is almost two-fold comparing the LDPE (240 MPa) and the LDPE þ60% HDPEx (450 MPa). This indicates a positive effect of the recycled HDPEx on the toughness of the filled LDPEs. Effect of the irradiation (same dosage and energy as at the recycled irradiated HDPE) on the HDPE is limited and represents only 6% growth. Strength of the material correlates with its toughness. The ultimate tensile strength increased only steadily; however, overall growth is almost 50% from 10.5 to 15.5 MPa (Fig. 8) and thus positive effect of recycled HDPEx was confirmed. Effect of the irradiation on the HDPE is little, yet again positive. Material hardness of the virgin and filled LDPEs increased from 53 to 59 ShD which is not a significant change (11%); however, positive effect of the recycled HDPEx filling remained unchanged (Fig. 9). Effect of the irradiation on the HDPE is still limited (65.6 vs 66.8 Shore D). Irradiation of the HDPE leads to an improvement mainly in the chemical, swelling, heat and stress cracking resistance (Drobny, 2013). Little influence of irradiation on HDPE's mechanical properties was proven; however, the main importance is that HDPEx can be used as a filler into the LDPE with the advantage of utilizing its better mechanical properties. 3.3. Structural analysis Fig. 10 shows that a strong interaction was developed between the matrix and the filler. The importance of the interaction has already been proven by many studies (Doufnoune et al., 2008; Tóth et al., 2004). Irradiation of the original HDPE might also help to strengthen adhesion and to overcome problematic miscibility of HDPE/LDPEs (Ženkiewicz et al., 2008). The basic purpose of the filling is to increase the bulk of polymer and improve its desired properties at low cost (Murphy, 2001).
Utilization of recycled irradiated material as the filler multiplies the cost savings and as this research paper shows, brings the added value of improved mechanical properties.
4. Conclusion The purpose of this paper was to investigate the possible utilization of the recycled irradiated HDPE. Usage of this material as the filler was proposed and its influence on processability and mechanical properties was investigated. Results show that there is on one hand a significant properties' improvement with the increasing amount of the filler but a decreasing processability on the other. Therefore, from the point of view of these properties, it is necessary to determine an optimal concentration of the filler. However the most important finding is that the recycled irradiated HDPE can be utilized as the filler into the virgin LDPE thus preventing generation of yet another plastic waste. This research paper offered a solution to dealing only with the recycled irradiated HDPE; however, other materials and combinations have to be investigated to make a general statement of utilization of the irradiated materials after the end of their lifetime.
Acknowledgment This research paper is supported by The internal grant of TBU in Zlin No. IGA/FT/2014/016 funded from The resources of specific university research and by The European Regional Development Fund under the project CEBIA-Tech no. CZ.1.05/2.1.00/03.0089.
References Adem, E., Avalos-Borja, M., Carrillo, D., Vazquez, M., Sanchez, E., Carreon, M.P., Burillo, G., 1998. Crosslinking of recycled polyethylene by gamma and electron beam irradiation. Radiat. Phys. Chem. 52, 171–176. Bhattacharya, A., 2000. Radiation and industrial polymers. Prog. Polym. Sci. 25, 371–401. Burrilo, G., Clough, R.L., Czvikovszky, T., Guven, O., Le Moel, A., Liu, W., Singh, A., Yang, J., Zaharescu, T., 2002. Polymer recycling: potential application of radiation technology. Radiat. Phys. Chem. 64, 41–51. Cheng, S., Phillips, E., Parks, L., 2010. Processability improvement of polyolefins through radiation-induced branching. Radiat. Phys. Chem. 79, 329–334. Cheremisinoff, N.P., 1998. Advanced Polymer Processing Operations, first ed. Noyes Publications, New Jersey. Doufnoune, R., Haddaoui, N., Riahi, F., 2008. The effects of coupling agent on the mechanical, rheological and thermal properties of calcium carbonate-filled LDPE compatibilized with maleic anhydride-g-LDPE (part II). Int. J. Polym. Mater. 57, 690–708. Drobny, J.G., 2013. Ionizing Radiation and Polymers: Principles, Technology, and Applications, first ed. Elsevier, Oxford. Fan, J.Z., Williams, M.C., Choi, P., 2002. A molecular dynamics study of the effects of branching characteristics of LDPE on its miscibility with HDPE. Polymer 43, 1497–1502. Gehring, J., 2000. With radiation crosslinking of engineering plastics into the next millennium. Radiat. Phys. Chem. 57, 361–365. Murphy, J., 2001. Additives for Plastics Handbook, second ed. Elsevier Science, Oxford. Nwabunma, D., Kyu, T., 2008. Polyolefins Blends, first ed. Wiley-Interscience, New Jersey. Rouif, S., 2005. Radiation cross-linked polymers: recent developments and new applications. Nucl. Instrum. Methods Phys. Res. B 236, 68–72. Tóth, K., Czvikovszky, T., Abd-Elhamid, M., 2004. Radiation-assisted PET recycling using glass fiber reinforcement and reactive additives. Radiat. Phys. Chem. 69, 143–147. Wypych, G., 2010. Handbook of Fillers, third ed. ChemTec Publishing, Toronto. Ženkiewicz, M., Czupryňska, J., Polaňski, J., Karasiewicz, T., Engelgard, W., 2008. Effects of electron-beam irradiation on some structural properties of granulated polymer blends. Radiat. Phys. Chem. 77, 146–153.
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Recycling of irradiated high-density polyethylene J. Navratil a,n, M. Manas a,1, A. Mizera a,2, M. Bednarik a,3, M. Stanek a,4, M. Danek b,5 a b
Tomas Bata University in Zlin, nam. T.G. Masaryka 5555, 760 01 Zlin, Czech Republic BGS Beta-Gamma-Service GmbH & Co. KG, Masarykova 378, 696 02 Straznice, Czech Republic
H I G H L I G H T S
Utilization of recycled irradiated material as a filler is proposed. LDPE/HDPEx mixtures were prepared in six concentrations. Processability and mechanical behavior were investigated and compared. Possible utilization of irradiated material after the end of its lifetime was proven.
art ic l e i nf o
a b s t r a c t
Article history: Received 5 March 2014 Accepted 29 June 2014 Available online 7 July 2014
Radiation crosslinking of high-density polyethylene (HDPE) is a well-recognized modification of improving basic material characteristics. This research paper deals with the utilization of electron beam irradiated HDPE (HDPEx) after the end of its lifetime. Powder of recycled HDPEx (irradiation dose 165 kGy) was used as a filler into powder of virgin low-density polyethylene (LDPE) in concentrations ranging from 10% to 60%. The effect of the filler on processability and mechanical behavior of the resulting mixtures was investigated. The results indicate that the processability, as well as mechanical behavior, highly depends on the amount of the filler. Melt flow index dropped from 13.7 to 0.8 g/10 min comparing the lowest and the highest concentration; however, the higher shear rate the lower difference between each concentration. Toughness and hardness, on the other hand, grew with increasing addition of the recycled HDPEx. Elastic modulus increased from 254 to 450 MPa and material hardness increased from 53 to 59 ShD. These results indicate resolving the problem of further recycling of irradiated polymer materials while taking advantage of the improved mechanical properties. & 2014 Elsevier Ltd. All rights reserved.
Keywords: Irradiation Radiation crosslinking Recycling High-density polyethylene Filler
1. Introduction The growing knowledge of properties' change of polymers after irradiation has led to an increasing usage of cheap, commodity plastics in the areas where it was unthinkable before. Several investigations of why there is such a boost in the spread of this technology have been done and it has been found that there are several reactions of exposed polymer materials including crosslinking, degradation and grafting (Cheng et al., 2010; Cheremisinoff, 1998). n
Corresponding author. Tel.: þ 420 576035152; fax: þ 420 576035176. E-mail addresses: [email protected] (J. Navratil), [email protected] (M. Manas), [email protected] (A. Mizera), [email protected] (M. Bednarik), [email protected] (M. Stanek), [email protected] (M. Danek). 1 Tel.: þ420 576035630; fax: þ 420 576035176. 2 Tel.: þ420 576035226; fax: þ 420 576035176. 3 Tel.: þ420 576035226; fax: þ 420 576035176. 4 Tel.: þ420 576035153; fax: þ420 576035176. 5 Tel/fax: þ 420 518324510. http://dx.doi.org/10.1016/j.radphyschem.2014.06.025 0969-806X/& 2014 Elsevier Ltd. All rights reserved.
Crosslinking is the most desirable reaction in order to enhance physical properties such as chemical resistance, mechanical behavior and thermal stability. Radiation crosslinking can be applied to thermoplastics, elastomers and thermoplastic elastomers (Rouif, 2005). Polyethylenes belong among one of the most radiation crosslinked materials. They crosslink without need of any crosslinking additive and they can be easily tailored to suit specific application (Rouif, 2005; Gehring, 2000). Three-dimensional polymer network is created in the crosslinked structure through branching of individual chains (Bhattacharya, 2000). Despite properties improvement, radiation crosslinked thermoplastic materials are losing their natural ability of being remelted repeteadly due to the network formation. This raises the issue of further waste processing. All previous research papers dealt with irradiation of recycled materials (Burrilo et al., 2002; Adem et al., 1998) but none of them dealt with recycling of the irradiated materials. This research paper offers a solution to this problem and it suggests an answer to it.
J. Navratil et al. / Radiation Physics and Chemistry 106 (2015) 68–72
2. Experimental part 2.1. Materials Low-density polyethylene (LDPE) was chosen as the polymer matrix regarding its good processability, low price and good availability. The commercial LDPE was supplied by The Dow Chemical Company - LDPE 780E. The melt flow index (MFI) measured according to the ISO 1133 standard at 2.16 kg load and 190 1C is 20 g/10 min. High-density polyethylene (HDPE) was chosen due to its wide spread in radiation industry and thus a great potential of being recycled, despite problematic miscibility with LDPE (Fan et al., 2002; Nwabunma and Kyu, 2008). This material was supplied in the form of irradiated floor heating pipes. Exact HDPE type used for their manufacturing was not determined; but, comparable “piping” HDPE type was used for comparison purposes. This material was supplied by Slovnaft Petrochemicals – HDPE Tipelin PS 380-30/302. The MFI measured according to the ISO 1133 standard at 5 kg load and 190 1C is 0.95 g/10 min.
2.1.1. Radiation processing Irradiation of these pipes was originally carried out at the BGS Beta–Gamma–Service company. Electron beam radiation was used for their irradiation, the dose was 165 kGy and the energy was 10 MeV, both parameters were set according to the HDPE manufacturer's recommendation. Dynamic method where rotating pipe (3601) is irradiated under the beam (irradiation direction was from the scanner from top quick vertical and in to the cross direction) on the conveyor was used to provide homogenous and uniform dose distribution. The required dose is determined according to the accelerator parameters (voltage, current, speed and amount of the windings of the conveyor) and its correctness is measured by gel content and by dosimeter. Nylon FWT 60-00 dosimeter was used to check the correct radiation dose, following analysis was carried out on spectrophotometer genesis 5 (calibration was according to the ASTM 51261 standard). Gel content of this material was measured according to the ASTM D7567 standard where it is determined by solvent extraction with xylene. Results shown that dose 165 kGy corresponds to 60% gel content.
69
2.2.1. Melt flow index Dynisco Kayeness LMI 4003 melt flow indexer was used for the MFI measurement of the proposed mixtures. Measurement was carried out in accordance with ISO 1133 standard at 2.16 kg load and 190 1C. 2.2.2. Polymer fluidity Testing laboratory injection mold with spiral cavity was used for the polymer fluidity determination. Length of the resulting spiral is up to 2 m and the cross-section shape is rectangular 6 1 mm2 (Fig. 2). Testing was done on the injection molding machine Arburg Allrounder 420C. 2.2.3. Flow curves Flow curves measurement was carried out on capillary rheometer Goettfert Rheograph 2001. Capillary L/D ratio was 20/1, testing temperature was 190 1C and shear rate range was from 35 to 2500 s 1. 2.2.4. Tensile test Tensile testing machine ZWICK 1456 was used for the tensile behavior estimation. Measurement was carried out according to the ISO 527 standard at ambient conditions. A crosshead speed of 50 mm/min was used throughout the whole measurement. E-modulus and ultimate tensile strength were evaluated from this measurement. 2.2.5. Shore D hardness OMAG AFFRI ART 13 Shore D hardness tester was used for hardness testing in accordance with ISO 868 standard. Hardness was measured on the same specimen as tensile behavior (Fig. 3). Measurement of all above mentioned properties was performed 15 times to ensure statistical correctness. 2.2.6. Structural analysis LEICA RM2255 microtome was used for the sample's preparation (thickness 35 mm) and microscope Olympus BX41 was utilized for the structural analysis.
3. Results and discussion 3.1. Processability
2.2. Methods Powder/powder mixtures of these materials were used in this investigation. Therefore recycled irradiated pipes were ground into a powder. Cleaned, chopped pipes were first crushed into the particles of 5 mm main size (Fig. 1) and then ground into the particles of 500 μm main size. LDPE powder was used as the polymer matrix and HDPEx powder was used as the filler. Materials were mixed in concentrations from 10% to 60%. Mixing was carried out in the laboratory fluid mixer for 5 min.
Fig. 1. Crushed pipes from recycled HDPEx.
Processing of the filled materials is a problematic operation and many factors have to be taken into account. For example the
Fig. 2. Spiral cavity plate and testing sample.
70
J. Navratil et al. / Radiation Physics and Chemistry 106 (2015) 68–72
Fig. 3. Melt flow index comparison.
Fig. 6. Resulting spirals: a) LDPE þ10% HDPEx, b) LDPE.
10000
LDPE LDPE+10% HDPEx
Shear viscosity [Pa.s]
LDPE+30% HDPEx LDPE+60% HDPEx
1000
HDPE
100
10
10
100
1000
10000
Shear rate [s-1]
Fig. 7. Elastic modulus comparison.
Fig. 4. Flow curves comparison.
Fig. 8. Material strength comparison.
Fig. 5. Polymer fluidity comparison.
viscosity increase/decrease depends on the properties of the filler, on the size of the filler etc. (Wypych, 2010). Melt flow index determination is a standard test of polymer flow behavior. Effect of the recycled HDPEx filler on the MFI is shown in Fig. 3. It can be seen that there is a substantial MFI decrease comparing the virgin LDPE and LDPEþ 10% HDPEx. Further addition of the filler results in a gradual decrease of the MFI. Overall drop is 96% comparing LDPE and LDPE mixed with the highest concentration of the recycled HDPEx. The MFI determines flow behavior only at low shear rates and thus higher shear rates have to be taken into account to fully describe the processing behavior. Flow curves were measured at shear rate up to 2500 s 1. In Fig. 4 flow curves of the three
Fig. 9. Material hardness comparison.
J. Navratil et al. / Radiation Physics and Chemistry 106 (2015) 68–72
71
Fig. 10. Resulting spirals: a) LDPE, b) LDPE þ 10% HDPEx, c) LDPE þ 30% HDPEx, d) LDPE þ 60% HDPEx.
different filling concentrations compared with the virgin LDPE and HDPE are depicted. It can be seen that the differences between each mixture are much higher at lower shear rates than at higher
shear rates where the differences are almost negligible. This result is in correlation with the statement that within the range of shear stress of 105–106 Pa (which is best suited for material processing)
72
J. Navratil et al. / Radiation Physics and Chemistry 106 (2015) 68–72
viscosity does not increase as rapidly (Wypych, 2010). The HDPE shows almost identical behavior to the LDPE with 30% of recycled HDPEx. The observed gap between the LDPE and the filled LDPEs remained unchanged even at higher concentrations. The spiral fluidity test simulates the real processing conditions the most closely. A huge drop of the polymer fluidity can be seen in Fig. 5 comparing the LDPE and the LDPE with 10% of the recycled HDPEx, this corresponds with the previously achieved results. Further increase of the filler negatively influenced the fluidity only gradually. Length of the spiral decreased from 50.5 mm to 20 mm comparing the filled LDPEs. The worst result was achieved at the virgin HDPE where the length was only 18 mm. In Fig. 6 resulting spirals are compared and where a significant difference between the filled and the virgin LDPE can be seen. It can be observed that the processability is strongly influenced by the filler. Even the lowest concentration of the recycled HDPEx caused a significant drop in the processability. It can be seen that the differences between filled LDPEs are very small. 3.2. Mechanical properties Dumb-bell shaped specimens with 10 4 30 (width thickness length) measurement area's dimensions were used for the investigation. Testing specimens were injection molded using the Arburg Allrounder 420C injection molding machine. Toughness of the resulting mixtures represented by the E-modulus is shown in Fig. 7. E-modulus grown constantly with the increasing amount of the filler. Despite big drop in the processability of the filled LDPEs the toughness growth is only steady. However the overall increase is almost two-fold comparing the LDPE (240 MPa) and the LDPE þ60% HDPEx (450 MPa). This indicates a positive effect of the recycled HDPEx on the toughness of the filled LDPEs. Effect of the irradiation (same dosage and energy as at the recycled irradiated HDPE) on the HDPE is limited and represents only 6% growth. Strength of the material correlates with its toughness. The ultimate tensile strength increased only steadily; however, overall growth is almost 50% from 10.5 to 15.5 MPa (Fig. 8) and thus positive effect of recycled HDPEx was confirmed. Effect of the irradiation on the HDPE is little, yet again positive. Material hardness of the virgin and filled LDPEs increased from 53 to 59 ShD which is not a significant change (11%); however, positive effect of the recycled HDPEx filling remained unchanged (Fig. 9). Effect of the irradiation on the HDPE is still limited (65.6 vs 66.8 Shore D). Irradiation of the HDPE leads to an improvement mainly in the chemical, swelling, heat and stress cracking resistance (Drobny, 2013). Little influence of irradiation on HDPE's mechanical properties was proven; however, the main importance is that HDPEx can be used as a filler into the LDPE with the advantage of utilizing its better mechanical properties. 3.3. Structural analysis Fig. 10 shows that a strong interaction was developed between the matrix and the filler. The importance of the interaction has already been proven by many studies (Doufnoune et al., 2008; Tóth et al., 2004). Irradiation of the original HDPE might also help to strengthen adhesion and to overcome problematic miscibility of HDPE/LDPEs (Ženkiewicz et al., 2008). The basic purpose of the filling is to increase the bulk of polymer and improve its desired properties at low cost (Murphy, 2001).
Utilization of recycled irradiated material as the filler multiplies the cost savings and as this research paper shows, brings the added value of improved mechanical properties.
4. Conclusion The purpose of this paper was to investigate the possible utilization of the recycled irradiated HDPE. Usage of this material as the filler was proposed and its influence on processability and mechanical properties was investigated. Results show that there is on one hand a significant properties' improvement with the increasing amount of the filler but a decreasing processability on the other. Therefore, from the point of view of these properties, it is necessary to determine an optimal concentration of the filler. However the most important finding is that the recycled irradiated HDPE can be utilized as the filler into the virgin LDPE thus preventing generation of yet another plastic waste. This research paper offered a solution to dealing only with the recycled irradiated HDPE; however, other materials and combinations have to be investigated to make a general statement of utilization of the irradiated materials after the end of their lifetime.
Acknowledgment This research paper is supported by The internal grant of TBU in Zlin No. IGA/FT/2014/016 funded from The resources of specific university research and by The European Regional Development Fund under the project CEBIA-Tech no. CZ.1.05/2.1.00/03.0089.
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