Comparison of Properties with Relevance for the Automotive Sector in Mechanically Recycled and Virgin Polypropylene

Polypropylene (PP) recycling has always been challenging because the polymer is highly susceptible to thermooxidative degradation during extrusion. Recycled (degraded) PP is normally blended with virgin PP to achieve reasonable mechanical properties after reprocessing operations. However, impurities present in recycled PP tend to degrade even the virgin PP in this process. In this study, standard recycled PP was produced in a laboratory by repeated extrusion and pelletization operations of virgin PP. This material was blended with virgin PP in a ratio from 3 : 7 to 7 : 3. An attempt was made to stabilize the recycled blend by adding a peroxide decomposer (triphenylphosphite, TPP) and a slipping agent (zinc stearate) in contrast to radical scavengers normally used in reprocessing. It was found that by using 0.3–0.5 wt % of TPP and 2 wt % of zinc stearate, this degradation could be effectively attested. Compared to the tensile strength retention of 68% (based on strength of pure virgin PP) of a 60 : 40 (recycled : virgin) PP blend without any stabilizer, a value of 77% was obtained for the same blend with the above-mentioned stabilizers. This stabilization effect was attributed to decomposition of unstable hydroperoxides to stable compounds in the recycled materials by TPP, and lower generation of new radicals in the presence of zinc stearate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3247–3251, 2004

Waste polypropylene (PP) polymer was collected, washed, dried and mechanically recycled into granules. Natural fibers are a sustainable and renewable resource, and in this work, Corchorus olitorius jute fiber was used as a reinforcing agent with waste PP. Jute fiber was collected from local market, cleaned, dried and cut into 1-2 mm in length for the production of waste PP-jute composites. The molecular structure of waste PP and virgin PP were characterized by the attenuated total reflection-fourier transform infrared (ATR-FTIR). The purpose of the current research was to examine the effectiveness of waste PP by comparing waste PP-jute composites and virgin PP-jute composites. The injection molding process was utilized to make jute fiber reinforced waste PP composites with various jute fiber loadings (5%, 10%, 15%, 20%, 25%, and 30% in weight).The same process was used to produce virgin PP composites reinforced with jute fiber. All composites undergo water absorption and tensile testing in order to assess the recycled PP. Injection molded virgin and waste PP's physico-mechanical, thermal, and tensile strengths are also examined. In comparison to waste PP, virgin PP has a 6% greater tensile strength and a 19% higher elongation at break. Results from waste PP-jute composites and virgin PP-jute composites did not significantly differ from one another. Products made from recycled PP can thus be both economically and environmentally viable.

Virgin polypropylene (PP), recycled polypropylene (RPP) and acrylonitrile butadiene rubber (NBR) were mixed together to prepare ternary blends (PP/RPP/NBR) of thermoplastic vulcanisates (TPVs). The blends comprised 30 parts per hundred (phr) NBR and 70 phr PP and RPP. Sulphur was used to dynamically crosslink the NBR during the blending process. Maleic anhydride grafted polypropylene (MA-g-PP) was used as compatibiliser to enhance the interaction of the polypropylene and the rubber. In this study, the loading of RPP in the TPVs was varied and the effects on mechanical and rheological properties were studied. The hardness and the tensile strength of the TPVs increased upon increasing the RPP loading. The RPP exhibited an adverse effect on elongation-at-break of the vulcanisates, with the pseudo-plastic flow behaviour and the viscosity of the vulcanisates increasing with the increased loading of RPP.

Polypropylene (PP) is a versatile polymer, with a wide range of applications, from household appliances to packaging and automotive components. Unfortunately, most of the PP products have a short life, which leads to a large amount of plastic waste. Recycling PP is an efficient way to offset the environmental pressure, and several technical solutions have been already proposed for PP recycling. However, dramatically reduced thermal and mechanical properties are generally obtained in the case of PP waste materials. In this work, the influence of PP waste on thermal and mechanical properties of PP waste/virgin PP blends was studied. A PP waste material (PPRR) was melted and compounded with high flow virgin PP homopolymer. The blends were characterized by dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, mechanical tests and Fourier transform infrared spectroscopy. An increase by 20% of the tensile strength and modulus and 2.5 times increase in the melt flow index were observed in the case of the blend with 50% virgin PP as compare to PPRR, also an important increase in crystallinity. All the blends showed a better thermal stability than the virgin PP. The results recommend the blends with 30–50% virgin PP for the recycling of PP waste from raffia in high-performance applications.

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

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

Parameters optimization for decontamination and fine physical regeneration pathways of polypropylene plastics from waste lunchboxes

UV accelerated aging of unidirectional flax composites: Comparative study between recycled and virgin polypropylene matrix

Several composites based on recycled—virgin polypropylene, wood flour and organically modified montmorillonite (commonly called ‘nanoclay’) were prepared by melt compounding. This paper aims to evaluate the potential for the use of recycled polypropylene and underutilized wood flour as material for the development of wood–plastic composites, as well as reinforcement effect of organically modified montmorillonite on them. In order to improve the poor interfacial interaction between the hydrophilic wood flour and hydrophobic polypropylene matrix, as well as polypropylene–organically modified montmorillonite, maleic anhydride-grafted polypropylene was used as a compatibilizer. Some mechanical and physical properties were evaluated. Findings of this work show that both recycled and virgin polypropylene can be used in manufacture of wood–plastic composites and there is no significant difference in the properties of resulting nanocomposites. It was found that mechanical properties of polypropylene containing 40wt% wood flour reinforcement remain essentially unchanged when the virgin polypropylene in the matrix is replaced be recycled polypropylene. Morphologies of the nanocomposites were analyzed by scanning electron microscopy and X-ray diffraction, and the results showed increased d-spacing of clay layers indicating enhanced compatibility between polypropylene and clay and wood flour. Consequently, polypropylene recycled from postconsumer applications can be used in high-value nanocomposites without going the expense of separating out impurities from the polymer.

Compositions of wood-polypropylene composites (WPCs) are prepared through melt compounding followed by injection moulding. WPCs are formulated for eight compositions with a different weight ratio of wood, virgin or recycled polypropylene and coupling agent. WPCs compositions are compared in terms of Melt Flow Index, Tensile, FESEM images, Flexural and crystallinity index for same operating variable conditions. From the results, recycled polypropylene based WPCs are superior in comparison to virgin polypropylene based WPCs. With the addition of 5 % coupling agent in recycled polypropylene-based composites for 45:50 composition, tensile and flexural values of WPCs are higher in comparison to all composition and neat virgin or recycled polypropylene. This work stands for the utilization of waste wood with recycled plastic for replacement of wood and virgin plastic.

As the demand for sustainable and environmentally conscious practices continues to grow, recycled plastics have become increasingly popular for plastics manufacturers. However, reprocessing these materials can result in inconsistencies in both process and product quality, leading to a loss in mechanical properties. To address this issue, this work investigates the injection molding of recycled and virgin polypropylene (PP). Using a multi‐cavity hot runner mold, correlations between processing parameters, such as melt temperature, mold temperature, pack pressure, soak time, and mechanical properties, were systematically investigated. A multivariate analysis approach was used to model the variables for each material. Results indicated significant correlations between processing, mechanical properties, and morphology. In particular, for the PP, the melt temperature affected the formation of β‐crystals and their transition to α‐crystals upon tensile testing. Different morphology was observed for the recycled polypropylene (rPP), in which crystallization was affected by polyethylene (PE) contamination. The results discuss the injection molding polymer, structure, and properties, relationship providing an approach to understanding and optimizing the mechanical properties of rPP. Highlights Polyethylene contamination in polypropylene significantly influences crystallinity. Recycling contamination reduces the polypropylene's ability to form β crystals. Virgin polypropylene mechanical properties can be tailored through processing conditions. Recycled polypropylene mechanical properties suffer at higher temperatures and residence times. Polypropylene α/β morphologies can be visualized after mechanical testing.

The physical and mechanical properties of wood-polymer composites made with virgin or recycled polypropylene, or a mixture of these were studied. The composites made with recycled polypropylene had higher density, lower porosity, and higher dimensional stability compared to the composites made with virgin polypropylene. Although the composites made with recycled polypropylene exhibited lower tensile strength than those made with virgin polypropylene, they had higher Charpy impact strength. Scanning electron microscopy analysis of the fractured surfaces of the composites showed no significant differences in the fracture mechanisms of the studied composites. The degree of crystallinity was estimated to be higher for the virgin polypropylene than for the recycled one.

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.

In this study, the effect of natural weathering on the physical and mechanical properties of wood plastic composites (WPC) made from virgin and recycled polypropylene (PP) was studied. To prepare the recycled PP, virgin PP was thermo-mechanically degraded by extrusion under controlled conditions in a single-screw extruder at a router speed of 60 rpm and temperature of 190 °C. PP (virgin and recycled), wood flour, compatibilizer, and UV absorbent were physically blended, and the samples were manufactured by a twin-screw extruder. The samples were exposed to natural weathering for 270 days. The surface characteristics of the samples were investigated before and after weathering. According to the results, the composites from recycled PP exhibited a higher weathering resistancethan those from virgin PP. The use of a UV absorber improved the flexural strength and modulus of the composites, but it could not significantly prevent the flexural properties loss and discoloration of the composites after weathering.

Polypropylene (PP)-based recyclates obtained specifically from mechanical recycling are increasingly used and visible in various application, e.g., bottles and containers in non-food applications. A big drawback of mechanical recyclates is that they contain besides the target polymer type, also other polymers and inorganic fillers, which are not soluble under the conditions required for polyolefins. These components make the analysis of recyclates with standard methods difficult. For virgin polypropylenes, it was shown that Crystex (CRYStallization EXtraction) analysis was capable of accurately determining the key properties for PP composition, like the amount of xylene cold soluble (XCS), the ethylene content, and the intrinsic viscosity (IV) of the whole material as well as of the crystalline and amorphous fractions. In this work, defined compounds with the same polypropylene composition but various filler contents were used for proving that the Crystex technique is a suitable analysis technique to determine the key properties of PP-based compounds in a fast and accurate way. Different types of sample preparation for removal of insoluble components prior to Crystex analysis were investigated and validated by different complex compounds, recycled PP, and PP-based compounds containing recycled material. It was concluded that by the usage of a newly developed online filter system, the key parameters in PP-based compounds and recycled PP can be determined without disturbance. Additionally, a new methodology was developed for a more accurate estimation of the non-intended polyethylene (PE) amount that does not originate from heterophasic PP (HECO-PP) in post-consumer recycled (PCR) PP material.