Development of a fast and robust analysis technique for determining the key properties in PP-based recyclates and compounds by Crystex technology

Polypropylene (PP) is a widely used polymer in packaging applications, which is often landfilled as part of #3–7 bales from material recovery facilities (MRFs). With rising demand for postconsumer PP, and its high composition in #3–7 bales, MRFs are increasing PP sorting capacity. Therefore, assessing chemical safety and physical quality becomes critical as design parameters for new products. Contamination emerges from various sources, for example, manufacturing, recycling and the original intended use (food compared with nonfood applications). Analysing the physical properties and contaminants/residual additives in postconsumer recycled (PCR) PP can provide guidance to improve cleaning, separation processes and quality reducing landfilling. PCR PP from #3–7 bale was sorted into two categories: food and nonfood applications. Each PCR PP type was exposed to a simulated recycling procedure and collected at each unit operation (washing, moulding, etc.) for analysis. It was determined nonfood‐application PCR PP contained higher quantitative phthalates, bisphenols and qualitative IAS/NIAS with inconsistent contaminant removal during washing. Nonfood‐application PCR PP possessed lower viscosity and molecular weight (Mw) across all categories except Mw in the unwashed sample compared with food‐grade PCR PP, likely due to contamination, polymer degradation or additive levels. This research identifies potential contaminants and additives in food‐ and nonfood‐application PCR PP from MRFs. These findings emphasise proper sorting for safe food‐grade feedstocks from postconsumer sources. These data indicate careful sortation is required to reduce exposure to chemicals of concern and unapproved additives in food packaging that comprised PCR PP.

The transport sector’s impact on climate change and energy-related greenhouse gas (GHG) emissions has raised significant concerns, prompting the automotive industry to transition towards greener solutions. This includes producing lighter vehicles with sustainable materials, like recycled plastics. Understanding the behavior of these new recycled compounds is crucial, especially regarding their response to ageing and stress conditions throughout a vehicle’s lifecycle. This study aims to investigate the mechanical property variations of virgin and recycled talc-filled polypropylene (PP) compounds used in the automotive industry, emphasizing the effects of thermal ageing after recycling. Polypropylene samples with different talc concentrations and post-industrial recycled content percentages are examined. Thermal (TGA and DSC) and spectral (FT-IR) analysis reveal structural changes due to recycling-induced thermo-mechanical degradation. A multi-axial impact test shows varied ductile and brittle behaviors between virgin and recycled PP, influenced by filler content. Impact strength, tensile, and flexural properties are assessed, highlighting differences between virgin and recycled PP, but maintaining properties over ageing time. Despite thermo-oxidative degradation from recycling and thermal ageing, the mechanical performance of recycled polypropylene materials remains unaffected, making them a viable sustainable alternative for the automotive industry.

The effect of adding virgin material or extra stabilizer on the recyclability of polypropylene as studied by multi-cell imaging chemiluminescence and microcalorimetry

The crystallization behavior, melting characteristics, and semicrystalline morphologies of wollastonite-filled recycled polypropylene (R-PP) composites without and with β-nucleating agent were investigated in this study. The crystallization temperature (Tc) of 20 mass% wollastonite-filled R-PP composite is 0.4 °C higher than that of R-PP, suggesting that the adding of wollastonite has little nucleation effect on crystallization of R-PP. However, 0.3 mass% TMB-5 significantly increases the Tc of R-PP and induces a large number of β-crystals in wollastonite-filled R-PP composites. For calcium pimelate-supported wollastonite (β-W) filled R-PP composites, the Tc and the relative β-phase content of R-PP increase with increasing addition amount of β-W (from 1 to 20 mass%). As a result, wollastonite-filled R-PP composites with β-phase content higher than 85% can be obtained by adding 0.3 mass% TMB-5 or 20 mass% β-W, which provides an effective method for realizing high value-added and low-cost recycling of R-PP.

Plastic recycling is a key aspect to achieve effective polymer circularity, especially for polyolefins for which usually the mechanical recycling is considered a downcycling process. This downcycling phenomenon arises from the progressive deterioration of the polymer microstructure during reprocessing, resulting in a gradual loss of processability and properties, ultimately compromising the possibility of using recycled polyolefins for applications with high engineering requirements.In this work, the effects of the thermomechanical degradation on the microstructure of polypropylene (PP) were assessed by subjecting the polymer to multiple extrusion cycles. The objective is investigating the evolution of the molecular weight and of the macromolecular architecture of PP typically occurring in a mechanical recycling process.Furthermore, a commercially available additive capable of restoring the PP molecular weight was introduced, with the purpose of proposing an effective upcycling strategy for achieving recycled PP with enhanced processability. In particular, the effects of the additive were evaluated following two different strategies that simulate pre-consumer or post-consumer mechanical recycling.The obtained results indicated that the introduction of the additive can effectively prevent the decrease of the molecular weight of reprocessed PP, also inducing some melt structuring phenomena associable with the introduction of some long chain branching and/or crosslinking. Finally, it was demonstrated that different macromolecular architectures for recycled PP can be achieved depending on the residence time during the processing in presence of the additive, opening new perspectives towards the possibility of obtaining recycled PP with modulable flow characteristics and, hence, processability.

Renewable raw materials and recyclable thermoplastic polymers provide attractive eco-friendly quality as well as environmental sustainability to the resulting natural fiber reinforced composites. We studied the possibility of using the recycled polypropylene (PP) for production of composites based on kenaf fibers (KF) and rice hulls (RH) as reinforcements. Polypropylene/rice-hulls (PP/RH/CA) and polypropylene/kenaf (PP/K/CA) composites with 30% fiber (filler) content and appropriate compatibilizing agent (CA)—a maleic anhydride grafted PP (MAPP), have been prepared by two steps procedure: melt mixing and compression molding. Flexural strength and thermal stability of the composites with recycled PP were similar to those with neat PP. The composites reinforced with kenaf fibers have shown better properties than those based on rice hulls. The flexural strength of the composite sample with recycled PP is 51.3 MPa in comparison with 51.1 MPa for the composite with neat PP. Degradation temperatures of neat and composite with recycled PP at residual weight 90% are 344.4°C and 343.5°C, respectively. The results obtained report the possibility of utilization of recycled PP for the production of natural reinforcements based composites with good mechanical characteristics for using as construction building materials in housing systems.

In this research, the improvement of the impact strength of wood flour–recycled polypropylene (PP) composites through impact modification was studied. For this purpose, a virgin polypropylene (VPP) was thermomechanically degraded by five extrusions under controlled conditions in a twin‐screw extruder at a rotor speed of 100 rpm and a temperature of 190°C. PP (VPP and recycled PP at the second and fifth stages) and wood flour were compounded at 50 wt % wood flour loading in a counterrotating twin‐screw extruder in the presence different contents of ethylene vinyl acetate (EVA) to produce the wood flour–PP composites. From the results, the composites containing recycled PP exhibited significantly lower impact strengths. The addition of EVA up to 9 wt % increased the impact strengths of the composites made with PP recycled two and five times by about 63 and 41%, respectively. The composites containing VPP exhibited higher impact strengths than those containing recycled PP and EVA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Influence of wood flour and modifier contents on the physical and mechanical properties of wood flour-recycle polypropylene composites

This study investigated the potential of using recycled manhole cover flour (CMC) and medium density fibreboard (MDF) sawdust as low cost fillers for recycled polypropylene (PP) composites. Various compositions of CMC and MDF flour, up to 40 wt% (20 wt% CMC and 20 wt% MDF), were compounded with recycled PP using maleic anhydride grafted PP. The results showed that increasing the filler content improved the bending strength and modulus, reaching 46.4 MPa and 3399 MPa, respectively, at 40 wt% loading. However, the tensile strength decreased slightly with the addition of 10 wt% filler and showed a slight decrease with the increase in filler content from 20 to 40 wt%. The water absorption of the composites showed only a slight increase from 0% for pure PP to 0.007% for composites with 40 wt% filler. Thermogravimetric analysis confirmed the thermal stability of the composites up to about 400°C. This study demonstrated the potential of using a blend of waste CMC and MDF flour up to 40 wt% to improve the strength and water resistance of recycled PP composites, offering a promising and sustainable approach to cost-effective composite production.

Recycled polypropylene (RPP) and lignin represent by-products produced in enormous amounts worldwide that remain underutilized. This study used rice straw lignin as a filler at various concentrations (0% to 70% w/w) in RPP and virgin polypropylene (PP) composites by melt blending. Structural and morphological alterations of lignin were analyzed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), respectively. Mechanical properties were evaluated using a universal testing machine (UTM). Results revealed that the tensile strength of the composites decreased as the lignin content increased, presumably due to the low of compatibility degree of lignin and MAPP, as well as the crack formation due to the agglomeration of lignin. However, composites with lignin as a filler showed higher moduli and water absorption capacities, as well as thickness swelling; using lignin as a filler caused a drastic reduction of the elongation at break values. The results indicated that the physical and mechanical properties of RPP and its virgin PP composites had no substantial differences. This indicated that virgin PP could be substituted by recycled polypropylene (RPP) for composite applications with the addition of MAPP.

A correlation between the variable melt flow index and the molecular mass distribution of virgin and recycled polypropylene used in the manufacturing of battery cases

European legislation, particularly the Packaging and Packaging Waste Regulation (PPWR), is rapidly increasing the demand for high-quality recycled polypropylene (PP) in packaging applications. Achieving such qualities through mechanical recycling remains challenging due to the heterogeneity of post-consumer waste, while the role of intensified washing in the overall decontamination remains debated. This study evaluates the influence of additional sorting and washing intensity on material properties, product performance, and environmental impacts in mechanical recycling of Dutch post-consumer rigid PP. White, clear, and colored fractions were processed under cold and hot wash conditions, extruded, and converted into cups by injection molding and thermoforming. Sorting effectively reduced feedstock heterogeneity, while hot washing slightly improved oxidation stability and ductility. Cup testing showed that the investigated recyclates achieved 77-88 % of virgin polypropylene top load performance. Hot washing removed surface contamination but did not significantly reduce volatile organic compounds or migration levels. A Life cycle assessment (LCA) was performed in openLCA using Ecoinvent background data. The results showed that advanced mechanical recycling, despite higher energy and chemical demand, remained environmentally advantageous, achieving significantly lower climate change impacts compared to virgin PP. However, the recyclate substitution rate in final products was identified as the dominant driver of environmental benefits. Overall, maximizing substitution and sorting efficiency proved more effective for achieving sustainable, high-quality PP recycling than intensifying washing.

The scientific community is currently confronted with critical problems in providing a healthy world for future generations. The study for sustainable plastic recycling methods is difficult for a variety of purposes. Indeed, during the previous century, the widespread usage of plastic materials has resulted in vast amounts of long‐lasting waste that has remained largely unaddressed by effective collection and disposal policies. Packaging materials are responsible for the majority of this waste which also includes polypropylene materials. However, environmental concerns imposed a new trend in the previous decade that brought this research under focus, as seen by the growing number of linked publications. For the recycling of polymeric plastic materials, several chemical and mechanical methodologies have been proposed. Due to the low ultimate tensile strain of concrete, plastic waste fiber materials have been used in concrete in recent times as the reinforced concrete components often function with cracks during the serviceability phase. The bonding strength and stress variation during flexure, toughening effect of a hybrid combination of steel and recycled polypropylene fibers on high‐strength concrete are investigated. Polypropylene's compressive and tensile strength, good dielectric characteristics, and acid and alkali resistance have all been observed in various studies. Hence the current review focus on the past researches on utilization of recycled polypropylene in concrete for the enhancement of its physical and mechanical properties.

Polypropylene (PP) has a high recycling potential. However, the properties of mechanically recycled PP (R-PP) have not been fully compared to those of virgin PP (V-PP). Therefore, in this study, properties of R-PP and V-PP were compared using data from recyclers, virgin plastic suppliers, and the literature. The properties of recyclates could not be directly correlated either with the properties of the virgin polymers from which the recyclates were made or the recycling parameters. It was found that the MFR of R-PP was higher; MFR R-PP had a median value (m) of 11 g/10 min while MFR V-PP had a median value of 6.3 g/10 min (at 230 °C and with 2.16 kg). In terms of mechanical properties, in many cases R-PP exhibited stiffer and more brittle behavior, with a slightly higher Young’s modulus (ER-PP = 1400 and EV-PP = 1200 MPa), a reduced elongation at break (ɛbR-PP = 4 l.-% and ɛbV-PP = 83 l.-%), and notched charpy impact strength (NCISR-PP = 4.8 and NCISV-PP = 7.5 kJ/m2). However, the values for every property had a broad distribution. In addition to existing information from the literature, our research sheds fresh light on the variation of the characteristics of recycled polypropylenes presently on the market.

A ‘model’ material of recycled polypropylene (PP) was prepared through the injection molding process, and the effect of processing history on the polymer characteristics was investigated through the high-speed melt spinning of virgin and recycled PP. On-line measurement of the thinning behavior of the spin-line revealed the downstream shift of solidification point for the recycled PP at the take-up velocity of 1.0 km/min, indicating the suppression of flow-induced crystallization. The difference was not clear at higher take-up velocities of up to 5 km/min. For any identical take-up velocity, no clear difference in the stress-strain curves and birefringence of the fibers from virgin and recycled PP could be observed, whereas the detailed investigation on the variation of relative amount of c-axis and a*-axis oriented crystals in the fibers prepared at varied take-up velocities suggested the deterioration of flow-induced crystallization at 1.0 km/min. It was speculated that the processing history induced the lowering of the entanglement density, which affected the melt spinning and crystallization behavior. An undistinguishable difference between the virgin and recycled PP at increased take-up velocities suggested the existence of an optimum elongational strain rate for the detection of the different states of molecular entanglement.