Waste Polypropylene Research Articles

Preliminary Research to Assess the Possibility of Grinding Selected Plastics Using Crushers

This study aims to investigate the effect of the shredding machine used on the recyclability of plastic fractions after primary crushing. This work presents a method for producing aggregates that has yet to be used in the plastics industry. This study included crushing of polymethylmethacrylate (PMMA), polyamide (PA-6), acrylonitrile butadiene-styrene (ABS), polycarbonate (PC), polystyrene (PS), and polypropylene (PP) waste in a jaw, a hammer, and a cone crusher. An analysis of the grain composition was carried out to characterize the obtained crushing products. The influence of feed size on the grain composition of the product and, only on the jaw crusher, the influence of the material used on the parameters of the crushing process was studied. This paper proposes a method to evaluate the grain composition and a way to assess plastic shredding capabilities based on machine kinematics and mechanical properties of a given material.

Durability and hardened characteristics of cement mortar incorporating waste plastic and Polypropylene exposed to MgSO4 attack

Annual waste plastic disposal has grown, harming nature. Utilising this waste in concrete production may help preserve building resources. This study tested cement mortar with polyvinyl chloride (PVC) and polypropylene (PP) substituted for sand aggregate at 0, 5, 10, 15, and 20%. The samples were nevertheless exposed to a 10% and 20% MgSO4 solution for a month. The properties of both fresh and hardened materials under these circumstances have been evaluated and contrasted with those evaluated under typical circumstances. For mixes including PP and PVC, the flow diameter increased. The rounded plastic particles provided fewer contact surfaces and less friction among mixtures, which reduced water consumption and improved workability, leading to an increase in slump flow. As the amount of plastic aggregate increases, the compressive strength decreased. Moreover, this pattern might be explained by the weakening of the bond between the surfaces of the plastic aggregate and cement paste. The hydration of cement may also be hampered by the hydrophobic properties of plastic aggregate. Like compressive strength, the splitting tensile strength decreased as the replacement level of plastic ratio increased regardless of its type under all conditions (normal and exposing to MgSO4). PP and PVC fine aggregate in mortar increases sorptivity under all situations. Following screening, those circumstances and PVC have the most impact on compressive strength. increasing PVC and PP at 10% for each of them leads to lower values of compressive and tensile strength. An optimization process was implemented to determine the optimum value of PVC, PP, and MgSO4. It shows that using PVC of 3.9%, PP of 10.1%, and MgSO4 of 19.59% leads to maximum compressive and tensile strength with the minimum cost and CO2 emissions.

Upcycling waste polypropylene with basalt fibre reinforcement enhancing additive manufacturing feedstock for advanced mechanical performance

This research seeks to overcome the printing and processing challenges of using waste polypropylene (PP) reinforced with short basalt fibres, transforming them into upcycled feedstock for additive manufacturing. It introduces an optimised method for producing filaments and 3D printing with these materials, addressing common issues such as adhesion and warpage through innovative techniques while achieving maximum mechanical performance in the resulting composites. Basalt fibre weight fractions of 0 %, 2 %, 5 %, 8 %, 15 %, 30 %, and 50 % were used to reinforce the recycled polypropylene, improving both printability and mechanical properties. The tensile strength reached 53.58 MPa at 15 % fibre content, while the flexural strength peaked at 34.06 MPa with 30 % fibre content, revealing distinct interactions between the fibres and polymer under tensile and flexural loading that were not previously observed. Microstructure, voids, debonding, and dispersion were examined using optical and scanning electron microscopy. Differential Scanning Calorimetry (DSC) was performed to assess the thermal behaviour and crystallinity of the recycled polymer during filament production and printing, revealing slight matrix degradation during these processes. The findings highlight the potential of waste basalt fibre-reinforced PP as a valuable filament feedstock for 3D printing, supporting a circular economy approach to composite manufacturing.

Sustainable Composites from Waste Polypropylene Added with Thermoset Composite Waste or Recovered Carbon Fibres

In order to limit the ever-increasing consumption of new resources for material formulations, regulations and legislation require us to move from a linear to a circular economy and to find efficient ways to recycle, reuse and recover materials. Taking into account the principles of material circularity and waste reuse, this research study aims to produce thermoplastic composites using two types of industrial waste from neighbouring companies, namely waste polypropylene (wPP) from household production and carbon-fibre-reinforced epoxy composite scrap from a pultrusion company. The industrial scrap of the carbon-fibre-reinforced epoxy composites was either machined/ground to powder (pCFRC) and used directly as a reinforcement agent or subjected to a chemical digestion process to recover the carbon fibres (rCFs). Both pCFRC and rCF, at different weight ratios, were melt-blended with wPP. Prior to melt blending, both pCFRC and rCF were analysed for morphology by scanning electron microscopy (SEM). The pCFRC powder contains epoxy resin fragments with spherical to ellipsoidal shape and carbon fibre fragments. The rCFs are clean from the matrix, but they are slightly thicker and corrugated after the matrix digestion. Further, the morphologies of wPP/pCFRC and wPP/rCF were also investigated by SEM, while the thermal behaviour, i.e., transitions and changes in crystallinity, and thermal resistance were evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The strength of the interaction between the filler (i.e., pCFRC or rCF) and the wPP matrix and the processability of these composites were assessed by rheological studies. Finally, the mechanical properties of the systems were characterised by tensile tests, and as found, both pCFRC and rCF exert reinforcement effects, although better results were obtained using rCF. The wPP/pCFRC results are more heterogeneous than those of the wPP/rCF due to the presence of epoxy and carbon fibre fragments, and this heterogeneity could be considered responsible for the mechanical behaviour. Further, the presence of both pCFRC and rCF leads to a restriction of polymer chain mobility, which leads to an overall reduction in ductility. All the results obtained suggest that both pCFRC and rCF are good candidates as reinforcing fillers for wPP and that these complex systems could potentially be processed by injection or compression moulding.

Investigation on the thermal, mechanical, and antibacterial properties of polymer nanocomposites from waste polypropylene and cerium oxide nanoparticles

Investigation on the thermal, mechanical, and antibacterial properties of polymer nanocomposites from waste polypropylene and cerium oxide nanoparticles

Functionalization and Repurposing of Polypropylene to a Thermoset Polyurethane.

Developing effective recycling pathways for polyolefin waste, enabling a move to a circular economy, is an imperative that must be met. Postuse modification has shown promising results in upcycling polyolefins, removing the limitation of inertness, and improving the final physical properties of the recycled material while extending its useful lifetime. Grafting of maleic anhydride groups to polypropylene is an established industrial process that enhances its reactivity and provides a convenient route to further functionalization and upcycling. In this work, maleic anhydride grafted polypropylene was hydroxylated and subsequently cured with a diisocyanate to form a thermoset polyurethane (PU). The crystal structure (unit cell and lamellar structure) of the polypropylene (PP) was preserved in the PU. At room temperature, the PU showed a high modulus due to the crystallization behavior of the PP; upon increasing the temperature above the melting temperature, the modulus decreased to a rubbery plateau, consistent with formation of a network. The resulting PU showed a higher glass transition temperature and lower degree of crystallinity than its PP predecessor due to the crosslinked nature of the polymer. The mechanical integrity of the PU was maintained through several reprocessing cycles due to the melt processability enabled by the presence of a urethane exchange catalyst. This functionalization and upcycling route thus offers a promising alternative to repurposing PP waste in which the creation of melt-processable thermoset polymers expands applications for the materials.

Assessment of Moisture Susceptibility of Hot Asphalt Mixtures Sustainable by RCA and Waste Polypropylene

Assessment of Moisture Susceptibility of Hot Asphalt Mixtures Sustainable by RCA and Waste Polypropylene

Towards sustainable construction: Harnessing potential of pumice powder for eco-friendly concrete, augmented by hybrid fiber integration to elevate concrete performance

This study investigates the innovative use of industrial waste pozzolana, specifically pumice powder (PP), as a partial replacement for cement, combined with hybrid fibers in concrete. Seven formulations varying PP content from 10 % to 35 % were tested, identifying 15 % PP as optimal. PP improved porosity due to its fineness, leading to better homogeneity, a refined microstructure, and an optimum compressive strength of 28.8 MPa with reduced permeability, enhancing durability. Hybrid fibers, including steel fibers (SF) from waste tires and polypropylene fibers (PF), improved toughness, ductility, and resistance to brittle failure. Tests on hybrid fiber-reinforced concrete (HyFRC) mixes with 1 % and 2 % hybrid fibers showed up to an 18.09 % increase in compressive, tensile, and flexural strengths. Energy dissipation in compressive response improved by 544.20 %, while flexural and splitting responses increased by up to 299.65 % and 208.57 %. Durability assessments in hydrochloric (HCl) and sulfuric acid (H2SO4) exposure revealed the synergy of fibers and PP enhanced resistance to chemical degradation, with high PF mixes losing as little as 0.04 % strength. Scanning electron microscopy (SEM) confirmed a dense, well-bonded matrix with reduced porosity. Analytical characterizations of mixtures such as energy dispersive x-ray spectroscopy (EDX) were studied. Regression models developed using Popovic’s and Mander’s models, accurately predicted HyFRC stress-strain behavior, closely aligning with experimental results. The integration of PP and hybrid fibers not only improved mechanical properties but also extended service life in harsh environments, offering a cost-effective, sustainable concrete solution.

Conversion of polypropylene (PP) plastic waste to liquid oil through catalytic pyrolysis using Philippine natural zeolite

Abstract The accumulation of plastic waste compelled the need to develop energy recovery methods, such as pyrolysis, which could convert plastics into valuable energy sources. Pyrolysis requires high operating temperatures; thus, a catalyst is often utilized to speed up the process. In this study, the viability of Philippine Natural Zeolite (PNZ) as a catalyst was investigated through the conversion of polypropylene (PP) waste into liquid oil using catalytic pyrolysis. The PP waste feedstocks were pre-mixed with the PNZ in a 1:10 ratio. Pyrolysis was carried out in a heating mantle for three trials of non-catalytic and catalytic pyrolysis. SEM and XRD were conducted to characterize the PNZ, while FTIR was carried out for the pyrolysis oil. SEM analysis showed the voids formed from the pores of the catalyst that influenced the pyrolysis reaction. Results from the XRD pattern also revealed clinoptilolite, mordenite, and heulandite as the main minerals found in the PNZ. Non-catalytic pyrolysis of PP yielded an average of 75.03% liquid oil, 13.66% residue, and 11.31% uncondensed gas. Meanwhile, catalytic pyrolysis produced higher yields with 86.39% liquid oil, 12.49% residue, and 1.12% uncondensed gas. FTIR results exhibited clear peaks for both processes, with similar components but different intensities.

VOC removal from automotive waste by supercritical CO2 extraction

This study investigated the reduction of volatile organic compounds (VOCs) from waste polypropylene (PP) from automobile bumpers by supercritical carbon dioxide (scCO2) extraction. The scCO2 extraction was performed with varying temperatures, pressures, and times in the range of 313–353 K, 10–25 MPa, and 1–6 h, respectively. At 333 K, 25 MPa, and 6 h, highly efficient removal of xylene, styrene, and total VOCs were observed, with removal percentages of >98 %. Optimal condition for VOC removal using scCO2 based on response surface methodology was determined to be 313 K, 10 MPa, and 2.17 h. No differences in size and color were observed in the scCO2-treated PP pellets. Moreover, VOC removal using scCO2 did not induce noticeable changes in the chemical and thermal properties of the treated PP samples. This result demonstrated that scCO2 extraction is a promising method for the VOC removal from automobile plastic waste.

Physio-mechanical, durability and microstructural properties of sustainable permeable concrete reinforced with basalt fiber: reuse and recycling of waste polypropylene

Physio-mechanical, durability and microstructural properties of sustainable permeable concrete reinforced with basalt fiber: reuse and recycling of waste polypropylene

Preparation and characterization of biochar/polypropylene composites from recycled waste plastics and agricultural waste-reed straw

To alleviate the increasingly serious plastic pollution problem, developing biomass-plastic composite materials has become a research hotspot. In this study, waste polypropylene (PP) and reed biochar (RC) are used as raw materials to prepare biochar/polypropylene composites (BPCs), and γ-aminopropyl triethoxysilane (KH550) is used as an interfacial modifier to improve the interficical compatibility between RC and PP. Benefiting from the coupling effect of KH550, the obtained KH550-modified reed charcoal/polypropylene (K-RC/PP) composites exhibit enhanced tensile and bending strengths compared to the RC/PP. When 2.4 wt% of KH550 is applied, the tensile and flexural strengths of K-RC/PP reach 22.77 MPa and 49.6 MPa, respectively. Moreover, the interfacial modification simultaneously improves the thermal stability and hydrophobicity of the composites, which not only significantly reduces the fire risks but also improves the durability of the material. This work provides a feasible solution for developing biochar/plastic composites with excellent mechanical performances and high fire safety.

Fractional distillation of waste plastic pyrolysis oil for isolating narrow hydrocarbons cuts

Pyrolysis of polyolefins generates a large amount of olefins, which can serve as a valuable feedstock for the synthesis of chemicals. Nevertheless, their effective utilization requires refining owing to their diverse carbon distribution. This study performed a comprehensive GC×GC analysis of pyrolysis oils derived from waste polypropylene (PP) and waste high-density polyethylene (HDPE). The chemical composition of PP pyrolysis oil exhibited a high content of iso-olefins, whereas HDPE pyrolysis oil contained mainly alpha-olefins. Experimental batch distillation of PP pyrolysis oil yielded narrow hydrocarbon cuts with iso-olefins content exceeding 70 wt%. In contrast, distillation of HDPE resulted in cuts with more than 25 wt% alpha-olefins content. To perform ASPEN simulations, the physical properties (density, viscosity) of the oil were determined, two ways for obtaining boiling curves (ASTM D2887 and ASTM D86) were compared and two property methods (Peng-Robinson and Soave-Redlich-Kwong) were compared. It was concluded that the ASTM D2887 boiling curve and the Peng-Robinson property method present better experimental agreement for pyrolysis oils using the Theil’s Inequality Coefficients test. Based on the validated batch simulation, continuous distillation process schemes for isolating narrow carbon cuts in the refinery atmospheric tower indicate that a side draw configuration provides a better yield of (19.1 wt%) compared to a dedicated separate distillation column of (11.9 wt%) for the same number of trays, while the dedicated column allows the possibility to achieve higher purity.

Ni doped carbon-based composites derived from waste cigarette polypropylene filter rod with electromagnetic wave absorption performance

Abstract Polypropylene is widely used in the plastics industry, especially in the tobacco industry, served as cigarette filters to reduce tar and harm. However, it’s difficult to degrade these polypropylene plastics and suitable methods for recycling and reuse is urgent. This research proposes an efficient method for the reuse of polypropylene cigarette filters by mixing waste polypropylene filters with nickel source in different proportions, followed by a facile calcination treatment to prepare nickel-modified carbon-based composite materials with excellent microwave absorption properties. Morphology and magnetic properties of as-prepared samples were analyzed via XRD, SEM, and VSM, exhibiting an increase in carbon content with raising nickel content. Nickel ion anchored on polypropylene fiber may facilitate better fixation of carbon chains during the polypropylene decomposition process. Among the as-prepared samples, CN2 exhibited superior microwave absorption performance, with an optimal absorption peak of -26.76 dB at 7.97 GHz when matched with a given thickness of 4.3 mm, and an effective absorption bandwidth of 3.64 GHz (8.04 GHz to 11.68 GHz) with a matching thickness of 3.5 mm, covering the X band. Therefore, the as-prepared microwave absorbers provides a feasible solution for the recycling and reuse of polypropylene filters, aligning with the tobacco industry requirements for green and sustainable development.

Recovering Valuable Chemicals from Polypropylene Waste via a Mild Catalyst-Free Hydrothermal Process.

Waste polypropylene (PP) presents a significant environmental challenge, owing to its refractory nature and inert C-C backbone. In this study, we introduce a practical chemical recovery strategy from PP waste using a mild catalyst-free hydrothermal treatment (HT). The treatment converts 64.1% of the processed PP into dissolved organic products within 2 h in an air atmosphere at 160 °C. Higher temperatures increase the PP conversion efficiency. Distinct electron absorption and emission characteristics of the products are identified by spectral analysis. Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) reveals the oxidative cracking of PP into shorter-chain homologues (10-50 carbon atoms) containing carboxylic and carbonyl groups. Density functional theory (DFT) calculations support a reaction pathway involving thermal C-H oxidation at the tertiary carbon sites in the polymer chain. The addition of 1% H2O2 further enhances the oxidation reaction to produce valuable short-chain acetic acids, enabling gram-scale recycling of both pure PP and disposable surgical masks from the real world. Techno-economic analysis (TEA) and environmental life cycle costing (E-LCC) analysis suggest that this hydrothermal oxidation recovery technology is financially viable, which shows significant potential in tackling the ongoing plastic pollution crisis and advancing plastic treatment methodologies toward a circular economy paradigm.

Mechanochemical Upcycling of Waste Polypropylene into Warm-Mix Modifier for Asphalt Pavement Incorporating Recycled Concrete Aggregates.

To solve the problems on resource utilization and environmental pollution of waste concrete and waste polypropylene (PP) plastics, the recycling of them into asphalt pavement is a feasible approach. Considering the high melting temperature of waste PP, this study adopted a thermal-and-mechanochemical method to convert waste PP into high-performance warm-mix asphalt modifiers (PPMs) through the hybrid use of dicumyl peroxide (DCP), maleic anhydride (MAH), and epoxidized soybean oil (ESO) for preparing an asphalt mixture (RCAAM) containing recycled concrete aggregate (RCA). For the prepared RCAAM containing PPMs, the mixing temperature was about 30 °C lower than that of the hot-mix RCAAM containing untreated PP. Further, the high-temperature property, low-temperature crack resistance, moisture-induced damage resistance, and fatigue resistance of the RCAAM were characterized. The results indicated that the maximum flexural strain of the RCAAM increased by 7.8~21.4% after using PPMs, while the sectional fractures of the asphalt binder were reduced after damaging at low temperature. The use of ESO in PPMs can promote the cohesion enhancement of the asphalt binder and also improve the high-temperature deformation resistance and fatigue performance of the RCAAM. Notably, the warm-mix epoxidized PPMA mixture worked better close to the hot-mix untreated PPMA mixture, even after the mixing temperature was reduced by 30 °C.

Insight into co-pyrolysis of waste polypropylene and engine oil for liquid hydrocarbons and interaction mechanism by kinetic analysis and DFT simulation

Plastic pyrolysis is an efficient and cost-effective way of processing plastic waste, producing oil, gas, and coke. Oil production from waste plastics is a promising technology, and co-pyrolysis of multicomponent materials can help to promote reactions and optimize the products. Therefore, this study examines the co-pyrolysis reaction of another hazardous waste, engine oil, with waste plastics. The co-pyrolysis performance of plastic is first evaluated and the TG-DTG curve is dynamically analyzed. Then the synergistic behavior of polypropylene and engine oil co-pyrolysis is revealed through a combination of experiments, kinetic analysis, and DFT calculations. For physical interactions, waste engine oil can improve heat and mass transfer performance during pyrolysis, significantly increase the heating rate of the reactants. Furthermore, the yield of liquid-phase products is increased. For chemical interactions, the optimal pyrolysis path was studied according to activation energies and the interaction mechanism was elucidated. Moreover, the optimal pyrolysis paths of the engine oil and PP were identical, with the resulting pyrolysis products having minimal difference in carbon chains. However, the detailed reaction paths need to be further explored owing to the complexity of the process. And the detailed composition of the pyrolysis products requires further comprehensive analysis.

Study of the thermal stability of spent bleaching clay-based geopolymer with waste polypropylene plastic aggregates

This study incorporated polypropylene (PP) plastic waste into the spent bleaching clay (SBC)-based geopolymer as aggregates, aiming to address pollution from plastic and edible oil industry waste while promoting a transition into circular economy of repurposing waste. The geopolymer mixture paste, containing PP plastic aggregates in different mass ratios (SBC:PP = 1:0.4, 1:0.6, 1:0.8, and 1:1) is oven cured at 60 °C and 80 °C for 8 h followed by 7 days of room temperature curing. Thermal properties of PP-SBC-based geopolymer mortars with varying compositions of PP plastic were assessed using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The TGA results revealed that the geopolymer's thermal stability within the temperature range of 620 °C–700 °C improved with an increase in PP plastic aggregate content, up to an optimal amount of 1:08 PPSBCG sample ratio of SBC to PP cured at oven temperature of 80 °C has been chosen as the representative sample for further discussion based on analysis result of ATR-FTIR spectroscopy and BET analysis. Beyond this amount, a reverse trend was observed. The DSC analysis revealed that incorporating PP plastic aggregates reduced its thermal stability towards the melting reaction but improved its thermal insulation properties. However, this effect was observed only up to a composition of PP plastic relative to SBC of 0.6, beyond this threshold, a reverse trend was observed. In addition to TGA and DSC, the geopolymer samples were characterized using Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) spectroscopy and N2 Brunauer-Emmett-Teller (BET) analysis. This study proved that the addition of high heat-resistant PP plastic into the geopolymer system increased the thermal stability of geopolymers, but only up to a certain optimal quantity. Excessive PP plastic resulted in a reverse trend due to significant effect of weakened interfacial bonding between the geopolymer matrix.

Production of cycloalkane-rich fuel by vacuum pyrolysis of mixed waste plastics using combined titanium and aluminum oxide: a preliminary investigation

The mitigation of plastic pollution constitutes one of the major challenges worldwide. Innovative research approaches have been solicited to improve the properties of fuel derived from plastic pyrolysis. The present study looks at the effect on the chemical composition of pyrolysis oil of the application in situ of a mixed metal oxide of titanium and aluminum in vacuum pyrolysis of mixed waste polyethylene, polypropylene, and polyethylene terephthalate. The experiment was performed at process parameters of 250 °C temperature, 79.9 Kpa vacuum pressure, and 1:10 catalyst-to-feedstock ratio, first without the mixed metal oxide (parent reaction) and then with the mixed metal oxide (modified reaction). The results showed that the presence of combined titanium and aluminum oxides in the reaction medium accounted for the presence of alkyl-substituted cycloalkanes at an area% of 33.97% in the liquid product, and a calorific value of 11,950 cal/gm was reported for the modified reaction. The parent reaction produced higher liquid and gaseous yields of 28.3% and 43.1% respectively while the modified reaction produced a greater percentage of char (23.8%) and residual wax(36.0%). The fuel properties of the liquid products obtained were equally determined.

Enhancement of concrete performance and sustainability through incorporation of diverse waste carpet fibres

Carpet fibres have demonstrated the potential to mitigate early-age cracking and improve tensile properties in concrete. However, a detailed analysis of the varied types of standard carpet fibres in reinforced concrete has been lacking. This study aims to bridge this gap by investigating the performance of concrete reinforced with widely used waste carpet fibres, namely Nylon, Polypropylene, Polytrimethylene terephthalate, and Polyester. The study employs fibres at 0.3 % and 0.5 % volume fractions with a 12 mm length. The research examines mechanical properties, shrinkage and cracking behaviour, pore structure, microstructure, and the ITZ. Results show that 0.3 % fibre volume yielded optimal performance based on GRA analysis. All fibre types reduced shrinkage compared to the control with no fibres. Nylon T1 at 0.3 % achieved a 22.3 % reduction at 90 days. Furthermore, fibre inclusion enhanced flexural and splitting tensile strengths up to 12 % and 39 % respectively due to fibre bridging, pore refinement, and reduced porosity. Notably, individual fibre mechanical properties influenced concrete performance significantly. Hydrophilic fibres exhibited a thinner 10 µm ITZ compared to 15 µm for hydrophobic fibres, contributing to denser interfacial regions and improved bonding. This study demonstrates the potential of carpet fibre-reinforced concrete as a sustainable solution, offering enhanced mechanical properties, shrinkage mitigation, and effective utilization of carpet waste, addressing critical issues in construction and waste management sectors.