Mechanical and Morphostructural Characteristics of Composite Materials Performed by Recycling Mixed Waste of Plastic and Paper

ROMEO CRISTIAN CIOBANU1, GHEORGHE BATRINESCU2, GEORGE ANDREI URSAN3, ALINA RUXANDRA CARAMITU4, VIRGIL MARINESCU4, ADRIANA MARIANA BORS5*, IOSIF LINGVAY4 1.SC ALL GREEN SRL, 8 George Cosbuc, 700470, Iasi, Romania 2.INCD ECOIND, 71-73 Drumul Podul Dambovitei, 060652 Bucharest, Romania 3.Technical University Gheorghe Asachi of Iasi, 53A Dimitrie Mangeron Blvd., 700050, Iasi, Romania 4.National Institute for Research and Development in Electrical Engineering INCDIE ICPE-CA, 313 Splaiul Unirii, 030138, Bucharest, Romania 5.ICPE-SA, 313 Splaiul Unirii, 030138, Bucharest, Romania

In order to evaluate the possibility of reuse of some mixed waste from plastic and paper, composite samples of both HDPE and PP basis were made with different filler contents of crushed postage envelope waste. From the morphostructural characterization (SEM images) of the samples obtained it was observed that the HDPE and PP samples had had a homogeneous single-phase structure in contrast to the composite samples with filler from mixed plastic and paper waste. The latter, have a biphasic heterogeneous structure in which the cellulose particles are uniformly distributed. Determinations performed through the dielectric spectroscopy technique indicated that the cellulose content of the composite samples leads to a systematic increase of the dielectric losses (up to about 40% for the HDPE samples, respectively about 30% for the samples with PP), the increases being in direct correlation with the cellulose content of the composite.Mechanical determinations have shown that the average values of tensile strength recorded on the achieved samples, systematically decrease at the increase in the chips content of the samplesdecreases up to 10% at an addition up to 15% chips from the waste are explained by the substantially lower mechanical strength of waste paper than that of the HDPE, respective PP.
Key words: waste, composite, HDPE, PP, filler, paper, dielectric loss, tensile strength In the perspective of a strong and sustainable development, the issue of adequate waste processing is a priority.
In this context, the recovery and reuse of waste materials is of particular importance, thus contributing to the reduction of environmental footprint, both by preventing environmental pollution (including persistent pollutants [1,5]) and preserving non-renewable natural resources (metals, hydrocarbons etc.). Polymeric materials during operation, under the action of stress factors specific to the operating environment, suffer a series of ageing processes by which functional characteristics degrade significantly [6][7][8][9][10][11][12][13]. In practice, waste containing polymeric material shows a great diversity (inseparable mixtures obtained from various polymers with or without metals, paper, wood, etc.), which makes their recovery and reuse by established methods impossible (involving the separation of each component in part).
In this context, the aim of the work is to obtain and characterize composite thermoplastic materials with filler of plastic and paper waste.

Experimental part
Waste of postage envelopes type with a content of about 50% polyethylene and 50 % paper, were shredded with a rotar y mill manufactured by VEB NOSSENER Maschinenbau. veb nossener maschinenbau. The chips were blended in various proportions by extrusion with powder of HDPE, of ELTEX type A3180PN1852 [31], respective polypropylene granules of Tipplen H 318 [32] type.
The extrusion of the chip mixes from HDPE waste, respective PP powders, was carried out in a laboratory extruder (Brabender-KETSE).
The working parameters on the extruder were: -extruder screw speeds of 45 rpm; -screw speed of hopper funnel: 700 rpm; -the temperatures on the heating zones of the extruder are shown in Table 1. paper particles are homogeneously distributed and well embedded in the polymer -the samples are no gaps.
The results of determinations by the dielectric spectroscopic technique are shown in Figure 4 for both samples based on HDPE (a) and PP (b), for various contents with filler from paper waste. In order to characterize the thermoplastic composites obtained from the M1-M8 granules, discs with a diameter of 30 mm and a thickness of 2.5 mm (for morpho-structural and dielectric characterizations) (Dr Boy-Germany injection machine) and bars with the section of 2.5 x 10 mm, with 100 mm long (to determine breaking strength) were injected.
The closing force of the injection mold was 350 kN, the temperatures of the injection machine heating zones are shown in Table 3.
Morpho-structural characterization of the obtained samples was performed by SEM microscopy with an equipment INCA Energy 250 energy dispersive spectrometer (EDS) -Oxford Instruments belonging Auriga (Zeiss) field emission scanning electron microscope (FESEM).
The amount of chips from waste samples obtained (composite granules) are shown in Table 2.
Characterization of the dielectric behavior of the obtained composites -determination of dielectric loss tgδ at 20 ± 2°C by dielectric spectroscopy technique with 1296 Dielectric interface / AMTEK -Solartron Analytical.
Determination of tensile strength by traction was performed with equipment MRCLAB -UTM 65B Universal Test Machine.

Results and discussions
The results of SEM determinations are shown in Figure 2 (injected samples based on HDPE) and in Figure 3 (injected samples based on PP).
The comparative analysis of the Figures 2 and 3 shows that the reference samples (M1 and M2 -from HDPE and pure PP) have a homogeneous (monophasic/single phase) structure and shows the imprint of the injection mold (inclined stripes).
On the samples with filler from paper waste, a heterogeneous (biphasic) structure is observed where the    Figures 4 a) and b) it is observed that in the range of 100-1000 Hz the dielectric losses on the reference samples (M1 -pure HDPE, respective M2 -PP pure) show approximately identical values and evolutions.
It is also noted that the cellulose content of the samples with paper filler (mixed chips from paper and plastic waste) leads to a systematic increase of the dielectric losses (up to about 40 % for HDPE samples, or about 30 % in the PP samples), the increases being in direct correlation with the cellulose content of the composite.
Thus, the increase in cellulose content also increases the dielectric losses.
This behavior can be explained by the content of polar -OH (hydroxyl) groups of cellulose which leads to increased dielectric losses.
The results of the mechanical strength measurements of the obtained composite samples, respectively the tensile strength values obtained, as well as the maximum differences ∆ max recorded between the five samples in each sample are shown in table 4.
Data analysis of Table 4 shows that the tensile strength of the samples based on PP are systematically higher by about 25% than those based on HDPE.
It is also noted that the maximum tensile strength differences recorded between the five samples in each sample are 0.02 MPa for samples with low content of chip from mixed waste of paper and plastic.
The value of 0.03 MPa was recorded on sample M5 (15% chips in HDPE) and M7 (10% chips in PP) and the maximum dispersion of 0.04 MPa was recorded only on sample M8 (15% chips in PP).
. It can be noticed that the average values of the tensile strength recorded, systematically decrease at the increase in the chips content of the sample.
The tensile strength evolution of the samples based on HDPE and on PP depending on the chips content from mixed waste of paper and plastic, is illustrated in Figures 5  and 6.
Losses of the tensile strengths (decrease of the mean values obtained on the average value determined on HDPE, respective PP pure) of the composites achieved depending on the chips content from waste of paper and plastic are shown in figures 7 and 8.   Figures 7 with 8, it is noted that the addition of chips from waste of the paper and polymer has a similar effect in both samples based on HDPE and on PP. This aspect also leads to a 10% tensile strength with an addition of up to 15% chips. This behavior to the mechanical stress of the composite samples can be explained by the tensile strength of the paper from chips substantially smaller than the HDPE, respective PP.

Conclusions
In order to evaluate the possibility of reuse of some mixed waste from plastic and paper, composite samples were made on both HDPE and PP basis with various filler contents of crushed postal envelope waste. From morphostructural, mechanical and dielectric characterization of the composite samples obtained by extrusion and injection, it was found that: -comparative SEM images recorded on the samples show a monophasic/single phase homogeneous structure in HDPE and pure PP samples and a biphasic heterogeneous structure for composites with filler from mixed waste of plastic and paper; -the cellulose content of the samples with paper filler ( mixed chips from paper and plastic waste) leads to a systematic increase of the dielectric losses (up to about 40% for HDPE samples, or about 30% in the PP samples), the increases being in direct correlation with the cellulose content of the composite -aspect explicable by including polar hydroxyl groups (-OH) in the nonpolar polymer of cellulose filler -the average values of the tensile strength recorded on the samples are systematically decreasing as the content of the chips in the samples increases. The decreases of up to 10% at an addition up to 15% chips from waste are explained by the much lower mechanical resistance of paper from waste than of HDPE, respective PP.
These findings lead to the conclusion that mixed waste of paper and plastic can be used to achieved composite material based on HDPE or PP for applications that do not require special mechanical and electrical performance.