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Appl. Sci. 2022, 12, 2867 9 of 20 Table 2. Mechanical properties of polyethylene before and after being recycled. Material before valorisation Material after valorisation Elasticity Modulus (MPa) 121.93 194.80 Yield Strength (MPa) 9.55 10.17 Breaking Strength (MPa) 13.16 14.28 Strain under Max. Load (%) 425.62 136.77 The material parameters were obtained before its valorisation. The mean value of the elastic modulus was 121.3 MPa, so it is a semi-rigid plastic (Et between 70 and 700 MPa). This indicates that in the elastic section, the increase in load produces relatively small deformations. At the breaking point there was an average stress value of 13.16 MPa and an average strain of 452.62%, see Figure 9. However, when analysing the results individually, it can be seen that, in the elastic section, the behaviour of the material remained almost constant, while in the plastic zone the results obtained were more heterogeneous, which means that the behaviour at rupture is more difficult to predict. On the other hand, the high percentage of strain indicates that it is a very ductile material. This characteristic is attributed to LDPE being a polymer with a branched chain structure. The ductility value also indicates that it is a polymer with high toughness, understanding this parameter as the amount of energy that a material absorbs before breaking. In the case of the material already valorised, the mean values obtained were: an elastic modulus of 194.80 MPa, yield strength of 10.17 MPa, and a breaking stress of 14.28 MPa. As far as ductility is concerned, the strain under maximum load was 136.77%. The results obtained from the different specimens show a low dispersion, so that the behaviour of the recycled polyethylene is almost constant. This is an indication that in the recycling process there were no problems of homogenisation or high porosity that would cause drastic drops Appl. Sci. 2022, 12, x FOR PEER REVIEW 10 of 21 in the material’s strength. If the change in behaviour of the material after its valorisation is analysed, the first thing that can be observed is the values of both breaking stress and yield stress have nointcarfefaescetdedbyth6e%starnendg9t%horefstphectmivaetleyr,iasol.iHtcoawnebveerc,otnhceluedlaesdtitchamtothdeulruecsyocflitnhgeprreoccyecslsinhgas wnaostianfcfreecatesdedthbeysatrpepnrgotxhimofattheelym5a9t%er.iaAl.tHthoewseavmeer, tihmee,lathsteicstmraoidnuulunsdoerf tmheaxriemcyucmlinlgoawdas ofinthcreemasaetderbiayldapecprreoaxsiemdabtyelaylm59o%st.7A0%t;ththeisamlsoeitnimdiec,athesetshtaratitnheutnednaecrimtyaoxfitmheumreclyocaldedof mtahtermiaaltiesrlioalwdeerc.reased by almost 70%; this also indicates that the tenacity of the recycled material is lower. Figure 9. Example of the effect of the test on a specimen. Figure 9. Example of the effect of the test on a specimen. 3.1.3. Hardness 3.1.3. Hardness Figure 10 shows a comparison of the Shore hardness D results on the material before Figure 10 shows a comparison of the Shore hardness D results on the material before and after assessment. and after assessment. The average shore hardness of the original polyethylene was 47.54, being 46.9 for the recycled polyethylene; in terms of shore hardness D, these values indicate that this polymer 51 can be considered hard. In view of the results, it can be concluded that the hardness of the material was not affected by recycling. On the other hand, although the hardness in poly5m0ers cannot be directly related to tensile strength (as it is in steels), it gives us an idea that the strength of recycled polyethylene must be similar to that of the original, as shown in previous sections. 49 48 47 ore hardness DPDF Image | Recycled Polyethylene Fibres for Structural Concrete
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