Recycled Polymer Blends Research Articles

Compatibility study of recycled Polypropylene (PP)/Poly(ethylene terephthalate) (PET) blends nanocomposites with PP‐g‐MAH: Modeling of twin screw extrusion

AbstractAlthough the utilization of recycled polymers is essential to sustain the environment, conventional recycled polymers face limitations in application due to the degradation of their properties caused by impurities. To solve the problem the performance deterioration of these recycled polymers, this study aimed to enhance their compatibility by chemically adding polypropylene‐graft‐maleic anhydride (PP‐g‐MAH) and physically manipulate a screw profile by using an extrusion simulation program. As a result of applying the optimized extrusion process set by the simulation program, significant improvements in the compatibility and dispersion of fillers within the polymer were observed through scanning electron microscopy image analysis. In addition, through detailed analysis of rheological data, the positive impact of adding compatibilizer and changing screw profile on rheological properties was demonstrated. As the compatibility of recycled polymer blends improved, tensile strength increased by approximately two‐fold and thermal conductivity was significantly improved, which were decisive factors in dramatically enhancing the performance of recycled polymers. These improved polymer properties provide an opportunity for recycled polymers to be applied more broadly and will expand the potential for new applications in various industrial fields.

Effect of Additives on Thermal Degradation and Crack Propagation Properties of Recycled Polyethylene Blends.

Additives, such as antioxidants (AOs), carbon black (CB) and compatibilizers (COs), are used in recycled polymer blends for different reasons. AOs slow thermal degradation, CB gives blends a black color and protect them against ultraviolet (UV) light, and compatibilizers improve compatibility between the different phases of the mixture and consequently enhance the mechanical properties of the final blend. In this paper, the three additives were added to recycled polyethylene (PE) blends to study their effect on the final properties and to determine the best formulations that help improve the mechanical properties of recycled PE blends. Stress Crack Resistance (SCR) was accessed by performing Notched Crack Ligament Stress (NCLS) and Un-notched Crack Ligament Stress (UCLS). On the other hand, Oxidative Induction Time (OIT) was used to determine the oxidation time of the blends and the effect of each additive on this property. Based on the results of this study, it was proven that adding carbon black and antioxidants delay the thermal degradation of recycled PE blends and consequently improve the OIT. Otherwise, resistance to stress cracking is improved only by adding a compatibilizer to the reference blend.

Thermomechanical Properties of Virgin and Recycled Polypropylene-High-Density Polyethylene Blends.

This paper provides evidence and discusses the variability in the thermomechanical behaviour of virgin and recycled polypropylene/high-density polyethylene blends without the addition of other components, which is sparse in the literature. Understanding the performance variability in recycled polymer blends is of critical importance in order to facilitate the re-entering of recycled materials to the consumer market and, thus, contribute towards a circular economy. This is an area that requires further research due to the inhomogeneity of recycled materials. Therefore, the thermal and mechanical properties of virgin and recycled polypropylene/high-density polyethylene blends were investigated systematically. Differential scanning calorimetry concludes that both the recycled and virgin blends are immiscible. Generally, recycled blends have lower overall crystallinity and melting temperatures compared with virgin blends while, remarkably, their crystallisation temperatures are compared favourably. Dynamical mechanical analysis showed little variation in the storage modulus of recycled and virgin blends. However, the alpha and beta relaxation temperatures are lower in recycled blends due to structural deterioration. Deterioration in the thermal and mechanical properties of recycled blends is thought to be caused by the presence of contaminants and structural degradation during reprocessing, resulting in shorter polymeric chains and the formation of imperfect crystallites. The tensile properties of recycled blends are also affected by the recycling process. The Young's modulus and yield strength of the recycled blends are inferior to those of virgin blends due to the deterioration during the recycling process. However, the elongation at break of the recycled blends is higher compared with the virgin blends, possibly due to the plasticity effect of the low-molecular-weight chain fragments.

Super-resolution Fluorescence Imaging of Recycled Polymer Blends via Hydrogen Bond-Assisted Adsorption of a Nile Red Derivative.

A key challenge in the recycling of multilayer plastic films of polyethylene and polyamide, as typically used for food packaging, is to assess and control the phase separation of the two types of polymers in the recycled material, the specifics of which determine the mechanical strength of the recycled material. However, visualizing the polyamide-in-polyethylene domains with conventional fluorescence methods or electron microscopy is challenging. We present a new approach that combines the point accumulation in nanoscale topography (PAINT) super-resolution method with a newly synthesized Nile Red probe (diOHNR) as the fluorescent label. The molecule was modified to undergo a hydrogen bond-assisted interaction with the polyamide phase in the blend due to its two additional hydroxyl groups but preserves the spectral properties of Nile Red. As a result, the localization density of the probe in the PAINT image is 13 times larger at the polyamide phase than at the polyethylene phase, enabling quantitative evaluation of the spatial polyamide/polyethylene distribution down to the nanoscale. The method achieved a spatial resolution of 18.8 nm, and we found that over half of the polyamide particles in a recycled sample were smaller than the optical diffraction limit. Being able to image the blends with nanoscopic resolution can help to optimize the composition and mechanical properties of recycled materials and thus contribute to an increased reuse of plastics.

Polymer blends manufactured from fresh & landfill mined plastic waste: Are they composites?

Plastics are primarily single-use and are disposed of in municipal solid waste landfills at the end of their life cycle. Such plastic waste undergoes partial degradation and results in the leaching of persistent contaminants such as surfactants, plasticizers, fire retardants, micro(nano)plastics, nanomaterials, etc., which are of great concern. Hence, the recovery and utilization of landfill-mined plastic waste (LMPW) and fresh municipal plastics waste (FMPW) is mandatory. Though thermal treatment techniques are widely used, they could treat only ≈8% of the total plastic waste generated due to their demand for pollution control measures which have been proven expensive. In this context, mechanical recycling, which allows the conversion of plastic waste into composites for different engineering applications, has been investigated by adding appropriate fillers. However, before creating composites, a comprehensive understanding of mechanically recycled waste plastics alone (read as blends) is necessary. This becomes important because most plastics used in domestic and industrial activities are significantly augmented by adding organic or inorganic constituents to achieve the target properties. Hence, the perpetual question, ‘whether the recycled polymer blends obtained from FMPW and LMPW are composites’ remains unanswered. This is key to decide upon the optimal dosage of the fillers to be used for achieving the target properties of the composites. To address these issues, extensive investigations were conducted to establish the overall characteristics of different blends obtained from FMPW and LMPW. Furthermore, after removing the polymeric component, the residues obtained from these blends were extensively characterized. This exercise revealed that the residues mainly constitute CaCO3, TiO2, and SiO2, which are either intentionally added while manufacturing virgin plastics or are due to contamination. It was also observed that the mechanical properties of the blends get enhanced due to the presence of residues, which indicates that these are composites and not blends.

Recycled plastic filament made from post‐consumer expanded polystyrene and polypropylene for fused filamant fabrication

AbstractThis research focused on developing recycled polymer blend filament from post‐consumer expanded polystyrene and single‐use polypropylene container for fuse filament fabrication (FFF). In this work, recycled polystyrene (rPS)/recycled polypropylene (rPP) blend was extruded into filament for FFF printing. The increase in printing temperature obviously reduced the air gaps and improved the interlayer adhesion. However, the printed specimen only exhibited optimum tensile strength at printing temperature of 230°C. The printed specimens with rPS/rPP at 80/20 blend ratio showed the lowest tensile strength due to poor printed layers adhesion caused by incompatibility of polymer blend. However, printed specimens with rPS/rPP at 50/50 blend ratio could achieve optimum strength of 32 MPa. The micrographs proved that the voids in printed specimen were smaller or absent when the printing temperature and rPP content in the blend was increased. This means that the increase in print temperature and rPP content displayed a positive effect on the printed specimens. The effect of blend ratio had significantly increased melt flow and crystallinity of rPS/rPP blend when the rPP content was increased in the blend. However, the increase of melt flow and crystallinity led to noticeable warpage on the printed specimen.

Mechanical Properties of Injection Molded Recycled High Density Polyethylene (rHDPE) Blends with pellets Low Density Polyethylene (pLDPE)

Recycling polymer has become a mandatory for sustainable development goals, life beyond water and land. Therefore, recycled polymer blends containing rHDPE/pLDPE (high density polyethylene and low density polyethylene) with composition 100/0, 80/20, 70/30, 50/50, 40/60, 30/70, and 0/100 have been prepared by melt compounding method using injection molding at 200 oC. Tensile testing shows that there is strong combination between rHDPE/rLDPE blends. Elongation at break differ from 122-230% and density test give results around 1.1 g/cm3. Injection molding process with the proper temperature setting and mixing of crushed plastic also affects the ductility, flexibility, brittleness and hardness of the specimen

On a contribution to study some mechanical properties of WEEE recycled polymer blends

AbstractThis research deals with the study of acrylonitrile‐butadiene‐styrene/polycarbonate (ABS/PC) totally derived from wastes of electrical and electronic equipment (WEEE). The aim of this study is to investigate the macroscopic use properties of 100% recycled polymers and compare them with the virgin materials. First, a preliminary work of sorting and characterization of the wastes was necessary to identify the predominant polymer components in the lots. Then, four compositions of blends (ABS/PC) were performed at laboratory using the twin‐screw extruder and injection techniques. Next, a series of experimental tests were carried out to investigate the morphology of the blends, their mechanical and thermo‐mechanical behavior. The experimental results highlighted the synergistic effect by blending ABS and PC wastes. In addition, the comparison with the virgin mixtures has shown a decrease in the mechanical properties of the waste blends, however, the mechanical behavior is still ductile and the blends stiffness was enhanced.

Compatibilized recycled polymers/clay as a matrix for rice husk composites: mechanical and physical properties

The growing green technological trend towards waste utilization and cost reduction has gained the industrial attention in the use of agricultural waste as a value added filler material. This research addresses a simple fabrication of greenly bionanocomposites made from polyethylene (rHDPE), recycled polyethylene terephthalate (rPET), nanoclay and rice husk (RH), with and without ethylene-glycidyl methacrylate (E-GMA) or maleic anhydride polyethylene (MAPE) compatibilizer, using a two-step twin-screw extrusion followed by hot/cold pressing. Results showed the positive effect in elongation at break and impact strength upon the reinforcement of nanoclay with the aids of compatibilizer as compared to the neat polyolefin blend. By adding RH, the flexural properties were found to increase remarkably up to 3.6 times than the blend matrix. It was found that the addition of compatibilizer, especially E-GMA, lowered the water absorption and thickness swelling of bionanocomposites. Scanning electron microscopy confirmed the improved compatibility of nanoclay with polymer blend upon the addition of compatibilizer. It can be concluded that the synergy effects of hybrid reinforcements of rice husk fibre and nanoclay in the recycled polymer blend have achieved while maintaining environmental appeal.

Influence of water absorptivity on kenaf fibre reinforced recycled-polymer composite properties

The hydrophilic nature of natural fibre in natural fibre composite (NFC) can reduce the material properties thus degrading the competitiveness of NFC as compared to synthetic fibre composite. This paper presents the water absorption effect on the mechanical properties of NFC made from kenaf reinforced recycled polymer blend. The recycled polymer blend is sourced from rejected-unused disposable diapers containing polypropylene and polyethylene (r-PP/PE). The kenaf flour fibre is compounded with r-PP/PE by using internal mixer machine with five variations of fibre loading which are 0, 30, 40, 50, and 60 wt.%. The water immersion test is conducted by immersing the samples in the distilled water for 24 hours as well as samples for tensile, flexural, and Izod impact tests. Experimental results show some improvement on some properties (impact strength) as well as degradation in other mechanical properties. The fractography analyses revealed the failure modes caused by fibre pull-out, matrix cracking, and fibre swelling and voids that induced micro cracks.

Structure and properties of compatibilized recycled polypropylene/recycled polyamide 12 blends with cellulose fibers addition

This research was aimed to develop engineering thermoplastic composites based on recycled plastics and cellulose fibers in order to provide eco‐friendly sustainable parts that meet certain requirements for automotive industry and to use recycled plastics for economic benefits. The composite networks were prepared using recycled PP, recycled PA12, two different maleic anhydride functionalized polypropylenes (PP‐g‐MA) and cellulose fiber. The loading of cellulose fibers was varied between 5 and 20 wt%. Based on the results of mechanical tests a substantial improvement was detected in terms of tensile and flexural modulus which showed that cellulose fibers could be used for reinforcing of stiffness of recycled polymer blends. It was also noticed that using PP‐g‐MA type of compatibilizers played an important role on the mechanical characteristics of polymer blends. The incorporation of cellulose into the compatibilized PP/PA12 blends resulted in higher storage modulus and shear viscosities than those of neat PP, PA12, and PP/PA12 blends at low frequencies and shear rates, respectively. Phase morphology of polymer blends and cellulose fibers‐filled composites became more fine, uniform, and stable with addition of PP‐g‐MA. Fourier transform infra‐red (FTIR) was used to confirm the interaction observed. It is obvious that cellulose reinforced, compatibilized recycled polymer blends can be a good alternative where better mechanical properties under high temperature are required in the automotive industry. This opportunity will help to reduce the cost and the effects of environmental issues. POLYM. COMPOS., 39:3556–3563, 2018. © 2017 Society of Plastics Engineers

Rice husk bio‐filler reinforced polymer blends of recycled HDPE/PET: Three‐dimensional stability under water immersion and mechanical performance

Green composite materials were made from agricultural and plastic wastes which were rice husk (RH), recycled high‐density polyethylene (rHDPE), and recycled polyethylene terephthalate (rPET), by twin‐screw extrusion and hot/cold pressing molding. The dimensional stability, orthotropic swelling, and mechanical performance of the green composites were determined as a function of bio‐filler concentration for neat (uncompatibilized) and compatbilized rHDPE/rPET blend based composites. Water absorption and swelling results showed a linear increase with the RH concentration. The highest swelling occurred in the thickness of the composites, followed by the width and length, respectively. Water absorption and dimensional instability of compatibilized recycled polymer blend (rPB)‐based composites were lower than those of neat rPB‐based composites. As RH concentration increased, the flexural properties increased significantly. The optimum tensile strength and modulus were achieved at 70 wt% RH. It is interesting to note that compatibilization of polymer blend matrix had further increased the strength and elongation properties of composites. POLYM. COMPOS., 39:2695–2704, 2018. © 2016 Society of Plastics Engineers

Biocomposites Based on Rice Husk Flour and Recycled Polymer Blend: Effects of Interfacial Modification and High Fibre Loading

Biocomposites were prepared with rice husk flour (RHF) (raw and alkali-treated) in a recycled polymer blend (RPB) using a co-rotating twin screw extruder. Modifications to the composite were carried out through fibre surface treatment with 4 wt.% sodium hydroxide (NaOH) and 3 wt.% maleic anhydride polyethylene (MAPE) coupling agent. Fourier transform infrared (FTIR) analyses of raw and NaOH-treated RHF were performed. The effects of the interfacial modification (MAPE or/and NaOH) and filler loading (50 to 80 wt.%) on the mechanical, physical, and morphological properties were investigated. Improvements in the tensile strength and Young's modulus as well as reduction in water absorption and water loss were observed for raw RHF composites incorporated with MAPE. Alkalisation of fibres resulted only in an enhancement in elongation and impact strength. The composite with 70 wt.% RHF modified with only MAPE exhibited the highest tensile strength and modulus, 22.2 and 711.6 MPa, respectively. The general trend of the composite results exhibited some decrease in water absorption and water loss from untreated RHF composites with only MAPE modification as compared to the NaOH-treated composite, although a rougher surface for the treated fibres was revealed in SEM images.

The Effect of Benzoyl Peroxide and Divinyl Benzene on the Properties of Cross-Linked Recycled Polyolefin Blends

The effect of peroxide cross-linking on the properties and morphology of recycled polyethylene (PE)/polypropylene (PP) blends was characterized. The addition of benzoyl peroxide (BPO) decreased the melt flow rate (MFR) and increased the impact strength of the recycled polymer blends. Divinyl benzene (DVB) is often used as a cross-linking agent assistant. Compared with BPO modification, the addition of BPO together with DVB improved the cross-linking efficiency and further increased the impact strength of the recycled polymer blends. The effect of BPO content on the MFR and the mechanical properties was also studied with the DVB content fixed. However, chemical cross-linking slightly reduced the thermal stability of the polymer blends. The morphology of the modified and unmodified polymer blends showed that with the addition of BPO, with or without DVB, the compatibility of the PE/PP blends was improved, resulting in enhanced impact strength.

Mechanical, water absorption, and morphology of recycled polymer blend rice husk flour biocomposites

ABSTRACTRice husk flour (RHF) biocomposites based on uncompatibilized and compatibilized recycled high density polyethylene/recycled polyethylene terephthalate (rHDPE/rPET) with ethylene‐glycidyl methacrylate (E‐GMA) copolymer were prepared through a two‐step extrusion and hot pressing with fiber loadings of 40, 60, and 80 wt %. Results showed that tensile and flexural properties increased. However, the elongation to break and impact strength decreased as the RHF loading increased. Compatibilizing polymer blend matrices can further enhance the mechanical properties. Water absorption (WA) test were examined in distilled and seawater. It is interesting to note that for composites made from uncompatibilized matrix, the calculated D and KSR were lower in seawater, but for the compatibilized matrix composites, the D and KSR obtained were generally lower in distilled water. However, compatibilization of rHDPE/rPET has been markedly reduced the WA and thickness swelling. Scanning electron microscope analysis of the compatibilized matrix composites confirmed the improved interfacial bonding of matrix–matrix and filler–matrix phases. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41494.

Improvement of ternary recycled polymer blend reinforced with date palm fibre

This paper investigates the study and preparation of date palm fibre reinforced recycled polymer blend composites. This is the first paper which describes the recycled polymer ternary blends of (1) recycled low density polyethylene (RLDPE), (2) recycled high density polyethylene (RHDPE) and (3) recycled polypropylene (RPP). The date palm fibre reinforced composites (CD00) were prepared by maintaining constant weight% of fibre of 20wt% without any fibre treatment. Maleic anhydride (MA) was used as the compatabilizer (1 and 2wt%) and the effect of compatabilizer on the blend matrix composites was studied. The mechanical, thermal, morphological properties, water absorption and chemical resistance properties were evaluated for these composites and also studied for pure blend matrix (C00). Date palm fibre improved the tensile strength and hardness of recycled polymer blend matrix. Further improvement was achieved with 1% MA (CD1), which showed that 1% MA treated composites (CD1) had higher tensile strength, modulus and hardness properties. Thermal stability and water absorption were improved by 1% MA. These improvements were demonstrated at the nanoscale level by the decrease in roughness appearing in Atomic Force Spectroscopic Microscopy analysis indicating that flow is better under this concentration. The SEM analysis also showed that the fibre matrix adhesion improved by adding 1wt% (CD1) of MA. The melting and crystallisation temperatures of the blends did not change with the addition of date palm fibre and MA, indicating that the additives did not influence the melting and crystallisation properties of the composites. The chemical resistance test results showed that these composites are resistance to all chemicals but more weight gain observed in solvents. 2wt% of MA (CD2) caused poor adhesion between the polymer chains and fibres as well as polymer chain scission.

Recycling of Mixed Plastics Waste Containing Polyethylene, Polyvinylchloride and Polyethylene Terephthalate

This research work was undertaken to investigate the spectroscopic, morphological and rheological properties of polymer blends made of recycled Polyethylene terephthalate (PET), Polyethylene (PE) and Polyvinylchloride (PVC). Different blends of these polymers were made by varying composition of PET. Each recycled blend consisted of recycled polymers and ethylene propylene diene monomer (EPDM) as a compatiblizer. Spectroscopic and morphological characteristics of recycled polymer blends were investigated using Fourier Transform Infrared Spectrometer (FTIR) and Scanning Electron Microscope (SEM) respectively. SEM analysis revealed low miscibility among these three polymers. While rheological properties were investigated using Melt Flow Indexer (MFI). The rheological characterization indicated that melt flow index (MFI) decreases with increase of PET concentration in PE/PET/PVC recycled blends. It was also observed that with increase of PET contents recycled blends show pseudoplastic behavior. DOI: http://dx.doi.org/10.3329/cerb.v16i1.17471 Chemical Engineering Research Bulletin 16(2013) 25-32

Influence of additives on recycled polymer blends

Polymer systems based on polymer waste offer promising way to increase recycling in the society. Since fillers play a major role in determining the properties and behavior of polymer composites, recycled polymers can also be combined with fillers to enhance the stiffness and thermal stability. In this study, blends of recycled polyethylene and recycled polypropylene with mica and glass fiber were prepared by melt blending technique. The effect of the particle loading, filler type, and filler–matrix interaction on thermal degradation and thermal transition of processed systems were investigated. Thermogravimetric analysis, differential thermogravimetric analysis, and differential scanning calorimetry were used in this investigation. Comparative analysis shows that both fillers produced different effects on thermal properties of the processed systems. These results were confirmed by calculating the activation energy for thermal degradation and thermal transition using Kissinger and Flynn–Wall expressions.

Modification of Recycled Polymer Blends with Activated Natural Zeolite

AbstractThe growing interest in the natural zeolite is based on some specific peculiarities of its structure, which after dehydration enables adsorption processes of some polymer molecules and/or segments to take place on the zeolite surface. The main goal of the study is to investigate the effect of dehydrated zeolite on the flow behavior, mechanical properties and morphology of immiscible blends from unsorted polymer wastes. A tetra‐component blend consisting of 40 wt.% polypropylene (PP), 40 wt.% high‐density polyethylene (HDPE), 15 wt.% low‐density polyethylene (LDPE) and 5 wt.% polystyrene (PS), was studied as a model system of commingled plastic wastes. Compositions from recycled blend and dehydrated zeolite in a wide concentration range (from 0 to 20 wt.%) were prepared using a twin‐screw extruder Brabender DSE 35/17D in the temperature range from 140 to 190 °C. The compositions were characterized by capillary rheometry, differential scanning calorimetry (DSC), site‐resolved wide‐angle X‐ray scattering (WAXS) and mechanical tests. The results show a compatibilizing effect of dehydrated zeolite at low concentration levels (1‐2 wt.%) and open wide possibilities for utilization of dehydrated zeolite in the recycling of unsorted polymer wastes.

Improvement of the mechanical properties of an HDPE/PS blend by compatibilization and incorporation of CaCO3

AbstractGenerally, recycled polymer blends exhibit solid dispersion‐like morphology with poor mechanical properties. The aim of this work was to enhance the mechanical properties of a HDPE/PS (75/25) blend, in particular the stiffness and the impact strength. In order to improve the stiffness, CaCO3 filler was incorporated. It was shown that PS and CaCO3 were separately dispersed with poor adhesion to the HDPE matrix. The incorporation of CaCO3 significantly enhanced the stiffness but lowers the impact resistance. Elastomer copolymers were incorporated in order to compensate for the embrittlement caused by the CaCO3 filler. Depending on their chemical structure, either grafted with a reactive function or ungrafted, the elastomers acted differently at the interfaces of the HDPE/PS/CaCO3 system. SEBS acts exclusively at the HDPE‐PS interface whereas SEBSgMA acts at both the HDPE‐PS and the HDPE‐CaCO3 interface. The SEBSgMA elastomer lowered the stiffening effect caused by CaCO3 and provided an insufficient increase in impact properties. One the other hand, SEBS, which concentrates its action at the HDPE‐PS interface, retained much of the stiffening effect of CaCO3 and provided a greater improvement in impact properties than SEBSgMA. In the recycled HDPE/PS (75/25) blend, the incorporation of 20 vol% CaCO3 and 4 vol% SEBS led to an increase in both impact strength (from 39 to 70 kJ/m2) and in stiffness (from 1335 to 1560 MPa). So, encouraging results were obtained, enabling us to predict a promising future for this approach to the recycling of commingled plastics.