Polypropylene Blends Research Articles

Dynamic behavior of melt electrospinning of blended polypropylene

Melt electrospinning is a promising process for fiber production without the need for solvents and with potential applications in various fields. In this study, we investigated the dynamic behavior of melt electrospinning under different blending ratios and process conditions. We used high melt flow index polypropylene and low molecular weight polypropylene, which were blended to lower the melt viscosity, and fibers were successfully manufactured through the melt electrospinning process. The effects of blending ratio and applied voltage on jet and drop formation, as well as fiber morphology, were examined. The results showed that blending low-molecular-weight polypropylene significantly influenced the jet and drop areas, leading to fluctuations in jet morphology. The size of the applied high voltage also had a high effect on the fiber diameter. Additionally, the viscosity reduction achieved through blending allowed for continuous jet formation and improved fiber production. These results provide valuable insights into controlling the process parameters and blending ratios in melt electrospinning, enabling the establishment of stable electrospinning conditions and precise control of fiber diameter.

Covalent Adaptable Network of Semicrystalline Polyolefin Blend with Triple-Shape Memory Effect

A covalent adaptable network (CAN) of semicrystalline polyolefin blends with triple-shape memory effects was fabricated by the reactive melt blending of maleated polypropylene (mPP) and maleated polyolefin elastomer (mPOE) (50 wt/50 wt) in the presence of a small amount of a tetrafunctional thiol (PETMP) and 1,5,7-triazabicyclo [4,4,0]dec-5-ene (TBD). The polymer blend formed a chemically crosslinked network via the reaction between the thiol group of PETMP and maleic anhydride of both polymers in the blend, which was confirmed by FTIR, the variation of torque during the melt mixing process, a solubility test, and DMA. DSC analysis revealed that the crosslinked polyolefin blends show two distinct crystalline melting transitions corresponding to each component polymer. Improved tensile strength as well as elongation at break were observed in the crosslinked blend as compared to the simple blend, and the mechanical properties were maintained after repeated melt processing. These results suggest that thermoplastic polyolefin blends can be transformed into a high-performance and value-added material with good recyclability and reprocessability.

Non-isothermal crystallization kinetics and activation energy modeling of carbon nanotubes dispersed high-density polyethylene and polypropylene blends

The study presents the effect of the reinforcement of carbon nanotubes (CNT) into high-density polyethylene (HDPE) and polypropylene (PP) blends. The Avrami exponent of CNT blends ranges within the 1.3–1.6 range. It demonstrates the 3D growth of crystals and nucleation activity during crystallization. The change in the Ozawa exponent indicates a two-stage crystallization process. The values of the Mo exponent show that the nucleation activity is affected by changing temperatures during the cooling process and the formation of high-quality crystal growth. The activation energy of the HDPE/PP matrix is 420.5 kJ/mol and adding 1.5% CNT resulted in 369.9 kJ/mol for Run-3. The polymer chains encounter difficulties in transitioning during the cooling process and release a significant amount of energy. The composition of the nanofiller in the blend affects the nucleation activity of the crystals. The permeability of the pure HDPE/PP sample obtained from sorption studies is 1.05 × 10−5 m2/s and adding 1.5% CNT in Run-3 provides a permeability of 5.2 × 10−5 m2/s. The CNT has a homogeneous dispersion in the matrix to form a net-like morphology. The crystallinity index calculated using the Seagal method for HDPE/PP, Run-3, Run-4 and Run-5 is 75%, 75.8%, 77.34% and 78%, respectively.

Quantifying the content of various types of polypropylene in high density polyethylene blends

To enhance the effectiveness of mechanical plastic recycling, it is best to separate different types of plastic during collection and recycling. This ensures the integrity and quality of recycled materials. For instance, the presence of polypropylene (PP) in recycled polyethylene (PE) can result in inconsistent and undesirable material, impacting the quality and performance of the recycled PE. This underscores the need for an analytical technique to accurately detect the presence of PP in recycled PE materials. In this study, we propose a quantitative analysis using a solution-based crystallization elution fractionation (CEF) technique to assess the polypropylene (PP) content in high-density polyethylene (HDPE) blends. The proposed methodology inherently distinguishes between the semi-crystalline PP matrix, including Homo-PP and Random copolymer PP, as well as the non-crystalline copolymer PP, and then quantifies each segment. A series of commercially available Ziegler–Natta catalyzed polymers were used to obtain the calibration curves per different type of PP materials, i.e., Homo-PP and Random copolymer PP. These calibration curves were then utilized to quantify Homo PP and copolymer PP (either semi-crystalline ethylene-propylene or amorphous ethylene-propylene) in different virgin polymer blends. The proposed methodology provides a comprehensive approach to characterizing the polypropylene content within polyethylene systems, especially in the context of qualifying polyolefin recyclate or polymer blends.

Influence of nucleating agent on the mechanical and thermal properties of neat isotactic polypropylene/reprocessed polypropylene blends

Influence of nucleating agent on the mechanical and thermal properties of neat isotactic polypropylene/reprocessed polypropylene blends

Polypropylene Blends with Durable Hydrophobicity and Enhanced Mechanical Properties Based on POSS and Alkane Modified Polypentafluorophenyl Methacrylate.

Durable functionalization on polypropylene (PP) surfaces is always a key problem to besolved. Coatings with low surface energy peel off easily especially under extreme conditions, owing to their weak adhesion. In this paper, side groups of both polyhedral oligomeric silsesquioxane (POSS) and alkane are grafted to polypentafluorophenyl methacrylate (PFP), and then PP blends with these side-group modified PFP are obtained through a melt-blending process. It is found that POSS can result in surface segregation and provide hydrophobicity in blends. Microfibers are formed because of the orientation effect during the tensile testing, which furtherly promotes mechanical strength. Significantly, alkaneside-groups can be entangled with PP segments, which brings about cross linking. Therefore, with crosslinking and synchronous orientation of POSS, the elongation at the break of blends is greatly increased up to 974%. The final blend demonstrates quite durable hydrophobicity under many extreme conditions, such as repeated tape peeling, ultrasonic washing, strong friction, and soaking in strong acid (pH = 1), strong alkali (pH = 14) and alcohol. The heat and UV resistance of the blend are also obviously improved. This study will develop anovel and facile strategy to endow PP with durable hydrophobicity as well as greatly enhanced mechanical properties.

Enhancing the Quality of Polypropylene Recyclates: Predictive Modelling of the Melt Flow Rate and Shear Viscosity.

The extensive use of polypropylene (PP) in various industries has heightened interest in developing efficient methods for recycling and optimising its mixtures. This study focuses on formulating predictive models for the Melt Flow Rate (MFR) and shear viscosity of PP blends. The investigation involved characterising various grades, including virgin homopolymers, copolymers, and post-consumer recyclates, in accordance with ISO 1133 standards. The research examined both binary and ternary blends, utilising traditional mixing rules and symbolic regression to predict rheological properties. High accuracy was achieved with the Arrhenius and Cragoe models, attaining R2 values over 0.99. Symbolic regression further enhanced these models, offering significant improvements. To mitigate overfitting, empirical noise and variable swapping were introduced, increasing the models' robustness and generalisability. The results demonstrated that the developed models could reliably predict MFR and shear viscosity, providing a valuable tool for improving the quality and consistency of PP mixtures. These advancements support the development of recycling technologies and sustainable practices in the polymer industry by optimising processing and enhancing the use of recycled materials.

Water Impact Dynamics and Mechanism Analysis of Polypropylene and Polypropylene/poly(ethylene-co-octene) Replica Surfaces with Nanowires under Low Temperature Conditions.

In this work, polypropylene (PP) and PP/poly(ethylene-co-octene) (PP/POE) blend replica surfaces with densely arranged nanowires are fabricated using a molding process. Morphology analysis shows that the nanowires on these replica surfaces have sharp tips and high aspect ratios. The droplet impact behaviors on the surfaces of the PP/POE blend replicas and PP replicas are investigated before and after freezing at -20 °C for 4 h. The height of the nanowires on the PP/POE blend replica surfaces is higher than that on the PP surface before and after freezing. The static wettability and droplet impact tests on the surfaces of PP/POE blend replicas and PP replica show that adding POE into the PP matrix can significantly increase the toughness of the nanowires on the PP/POE blend replica surfaces during the droplet impact at low temperatures. These investigations are favorable to broaden the practical applications of superhydrophobic surfaces in some severe environments.

In‐mold rheology and automated process control for injection molding of recycled polypropylene

AbstractManufacturing plastic parts with secondary feedstocks has risen to the forefront of importance in recent years. However, the variation in molecular weight and rheology of secondary feedstock can lead to inconsistent part quality. This work evaluates the effectiveness of a novel closed‐loop adaptive process control system that adjusts nozzle pressure in response to in‐mold pressure data. Five different recycled polypropylene blends, with a broad distribution of flow properties, were evaluated to determine the effectiveness of the control system at reducing processing variation. The experimental results show that the process control strategy reduced the variation within the mold, as seen by in‐mold pressure curves and calculated in‐mold viscosity values. Additionally, the parameters that control the automated process adjustments were investigated, showing the importance of optimization. The analysis of the correlation between in‐mold rheology and mechanical properties showed a slight variation in the mechanical properties and parts weight with a coefficient of variation of under 5%. Overall, the results demonstrate the ability of pressure‐controlled molding and automated viscosity adjustment to reduce the variability when molding a secondary feedstock.Highlights Pressure‐controlled injection molding of recycled polypropylene. Automated closed‐loop adaptive process control methodology. Methodology resulted in a reduction in pressure variation during molding. Changes in mechanical properties and in‐mold viscosity were investigated. Results show the potential of pressure‐controlled molding at reducing variation.

Improving 3D printability and interlayer adhesion in ABS/PP immiscible polymer blends

AbstractPrintability and interlayer adhesion are the most critical issues in 3D printing of immiscible polymer blends. It can affect structural integrity and mechanical performance of the printed parts. In this work, an effective strategy to improve the printability and interlayer adhesion of immiscible acrylonitrile‐butadiene‐styrene/polypropylene (ABS/PP) blends was implemented by introducing styrene–ethylene/butylene–styrene copolymer grafted with maleic anhydride (SEBS‐g‐MA) as a compatibilizer. The printability of the developed blends was investigated using rheological properties such as absolute value of complex viscosity, loss tangent and die‐swell ratio. Interestingly, it was found that the additive manufactured blends with 20 wt% SEBS‐g‐MA loading showed improved interlaminar shear strength, impact strength, Young's modulus and toughness as compared with the pure blend. Fractography analysis revealed that two different possible failure mechanisms, interface and matrix failure were apparent in the 3D printed samples with and without SEBS‐g‐MA content. This work provides a promising pathway to fabricate the complex structures from polymer blends with improved mechanical properties and surface finish.Highlights This study demonstrated improved interlayer adhesion at the printed interface of immiscible ABS/PP blends in presence of SEBS‐g‐MA. The printability of the developed blends was predicted from rheological properties. Additive manufactured blends with SEBS‐g‐MA loading showed improved mechanical performance.

Pronounced shear-induced crystallization of polypropylene by addition of poly(methyl methacrylate)

The shear-induced crystallization of polypropylene (PP) in immiscible blends with poly(methyl methacrylate) (PMMA) was studied using three types of PMMA samples with different molecular weights. The addition of low-molecular-weight PMMA greatly enhanced the shear-induced crystallization of PP. Because the low-molecular-weight PMMA had low viscosity at high temperatures, the PMMA droplets dispersed in the PP were deformed in the flow direction and subsequently turned fibrous. As the temperature decreased, the viscosity of PMMA increased greatly prior to PP crystallization. Consequently, the deformed PMMA dispersions were hardly deformed further in the molten PP. It provided excess stress for PP in the flow direction, leading to a large Rouse-Weissenberg number. They thereby accelerated shear-induced crystallization of the PP. Because of the pronounced shear-induced crystallization, the orientation of the PP chains, which causes high rigidity, was greatly enhanced.

Experimental and theoretical investigation of the effect of physical and chemical compatibilization on the properties of thermoplastic elastomers derived from natural rubber and polypropylene blends

The objective of this research was to improve the compatibility between Natural Rubber/Polypropylene NR/PP blends through physical and chemical compatibilization methods. The physical compatibilization involved the use of epoxidized natural rubber/maleic anhydride-grafted polypropylene (ENR50/PP-g-MA) as a dual compatibilizing agent (CA50), while the process of reactive compatibilization entailed chemically modifying NR and PP phases through the grafting maleic anhydride (MA). Several formulations were prepared by melt mixing using a Brabender plasti-corder. The effects of physical and chemical compatibilization on the technical properties were investigated. FTIR analysis revealed the emergence of two distinctive peaks corresponding to the CO group of MA grafted onto PP and NR chains. FTIR analysis has also confirmed the taking place of reactions between the polar functional groups of PP-g-MA and ENR50. The rheological properties indicated that the viscosity of the NR-g-MA/PP-g-MA is lower than those of the control blend and CA50-based NR/PP system. The mechanical and dynamic mechanical findings corroborated the improvement of interfacial adhesion between NR/PP phases, especially for the NR/PP/CA50 system. SEM examination demonstrated a more uniform dispersion of the PP phase in the CA50-based NR/PP, compared to the control blend and NR-g-MA/PP-MA. NR-g-MA/PP-g-MA exhibits greater miscibility and interaction potential compared to the control NR/PP, and less than NR/(ENR50/PP-g-MA)/PP system. DFT calculations further validate the effect of compatibilization methods on TPE blends. Specifically, Quantum molecular descriptors revealed the role of ENR50/PP-g-MA as an intermediary in facilitating compatibility between NR/PP. These findings indicate that the physical compatibilization method approach using ENR50/PP-g-MA as a dual compatibilizer is a potential compatibilizer for NR/PP.

Enhancing poly(lactic acid)/maleated polypropylene blend with magnesium oxide catalyst: a reactive blending approach for improved mechanical properties

Some defects of polylactic acid (PLA), especially its poor mechanical properties, were modified using a minimum content of non-biodegradable maleated polypropylene (MAPP). To this end, first, the amount of MAPP was optimized, which was 20 wt.%. Second, MgO was used as a new catalyst to improve the exchange reactions between active groups in both polymers in a reactive blending process. Tensile and izod analyses showed that, compared to neat PLA, with a slight decrease in modulus and tensile strength, elongation at break, and impact resistance were improved in the presence of 20 and 0.1 wt.% of MAPP and MgO, respectively. This improvement in mechanical properties can be related to the exchange reactions between two polymers and the formation of PLA-MAPP block copolymers. MFI and WDCA analyses demonstrated the increase in melt flowability and surface hydrophilicity of the resulting blends, respectively. DSC analysis showed that the Tg values of both polymers approached each other in the presence of catalyst. Also, the elimination of cold crystallization of PLA and the decrease in the Tm and crystallinity of both polymers are clear reasons for the miscibility of the alloy. TEM displayed the proper dispersion of MgO nanoparticles within the polymer matrix, and in addition, the XRD test also proved the decrease in the crystallinity of both polymers and appropriate miscibility of the samples containing 20 and 0.1 wt.% of MAPP and MgO, respectively. These results can promise the design of a compound with the maximum amount of PLA for further use in various industries.

Effects of nanomagnesia and polypropylene-graft-maleic anhydride on the dielectric breakdown properties of polypropylene/ethylene propylene diene monomer blend

Thermoplastic polypropylene (PP) has garnered a significant attention in power cable insulation research because of its exceptional thermal tolerance and dielectric properties. Due to its poor impact strength at room temperature, PP has been blended with various elastomers, including ethylene-propylene-diene monomer (EPDM), to improve the mechanical stiffness of the final material. This, however, comes with compromised dielectric properties of the material. Recently, the addition of nanofillers to polymers has demonstrated promising properties that can be tailored for various dielectric applications, provided that nanofiller and polymer interactions are appropriately formulated. Nevertheless, the effect of nanostructuration in PP/elastomer blends, especially from the perspective of dielectrics, have yet to be systematically explored. In the current work, magnesia (MgO) nanofiller is added to a model PP/EPDM blend system to determine the effect of MgO on the breakdown properties of PP/EPDM. The results show that adding 0.5 wt% of MgO to PP/EPDM reduces the AC and DC breakdown strengths by 7% and 16%, respectively. As the amount of MgO increases to 3 wt%, the AC and DC breakdown strength reduces further by 25% and 29%, respectively. Significantly, appropriate modification of the nanocomposites with polypropylene-graft-maleic anhydride (PP-g-MAH) can result in 5% higher breakdown strength of the nanocomposites with respect to comparable nanocomposites without modification. The mechanisms surrounding these breakdown effects are discussed with the aid of materials structure interpretations. Overall, the results demonstrate that appropriate modification of nanocomposites with PP-g-MAH is crucial in tailoring breakdown properties of PP blend nanocomposites.

Rheological insights into the degradation behavior of PP/HDPE blends

The (re-)processing and degradation behavior of polypropylene (PP) blends with high-density polyethylene (HDPE) is a crucial topic in mechanical recycling due to the prevalence of PP/HDPE mixtures. In particular, small amounts of cross-contamination (below 10.0 wt.%) between these polyolefins are quite common. While much empirical data is available, systematic studies on such blends are scarce and rarely account for the polymers’ chain structure. This study employs time-resolved rheology, atomic force microscopy (AFM), differential scanning calorimetry (DSC) and chemiluminescence techniques to study the degradation of different PP types containing 0.5 to 10.0 wt.% of HDPE. It is observed that the addition of small amounts of HDPE can result in a prominent change in the viscoelastic properties of PP during the thermo-oxidative degradation. The substantial evolution of elasticity in the blends is mainly related to the gelation of fine PE particles dispersed within the PP matrix. It is also shown that a smaller viscosity ratio between the blend components can lead to a more significant degradation through morphology alterations. Remarkably, time-resolved rheology studies revealed that even a small amount of HDPE (2.5 wt.%) can lead to a reduction in the thermo-oxidative stability of the PP/HDPE blend through excessive branching/crosslinking of the HDPE phase. This effect was particularly more pronounced when the PP contained an ethylene comonomer in its backbone. The finer morphology of PE particles in PP copolymer can exacerbate the thermo-oxidative stability of the blend. These insights are essential in designing new life cycles for recycled PP cross-contaminated with HDPE, typically found in the light fraction of municipal solid plastic waste.

Effect of Ethylene-Propylene-Diene Monomer Blending on the Dielectric Properties of Polypropylene for Power Cable Insulation

Thermoplastic materials such as polypropylene (PP) are ideal candidates to be used as power cable insulation materials. However, the mechanical properties of PP, which is brittle and stiff, need to be modified to meet the requirements of power cable insulation applications. To overcome this, ethylene-propylene-diene monomer (EPDM) can be melt blended with PP to improve PP’s mechanical properties. In the current work, the effect of blending different contents of EPDM with PP was investigated in terms of the morphology, chemical structure, dielectric response, electrical, and mechanical properties. The results show that the EPDM blended well with the PP as the EPDM dispersed in the PP structure. Meanwhile, the chemical structure and dielectric response of the EPDM and PP blend became slightly different with high contents of EPDM, which subsequently affected the breakdown strength and mechanical properties. Nevertheless, it is worth noting that PP blended with low contents of EPDM has the potential to be used as recyclable power cable insulation materials.

Analysis on Isotropic and Anisotropic Samples of Polypropylene/Polyethyleneterephthalate Blend/Graphene Nanoplatelets Nanocomposites: Effects of a Rubbery Compatibilizer.

Over the past few years, polymer nanocomposites have garnered a significant amount of interest from both the scientific community and industry due to their remarkable versatility and wide range of potential uses in various fields, including automotive, electronics, medicine, textiles and environmental applications. In this regard, this study focuses on the influence of a compatibilizer rubber on a nanocomposite incorporating graphene nanoparticles (GNPs), with a polymer matrix based on a blend of polypropylene (PP) and polyethylene terephthalate (PET). This effect has been investigated on both isotropic samples and on anisotropic/spun fiber samples. The influence of the compatibilizer rubber on morphological, rheological and mechanical properties was analysed and discussed. Mechanical and morphological properties were evaluated on both isotropic samples obtained by compression moulding and melt-spun fibers. The addition of the rubbery compatibilizer increased the viscosity, improving interfacial adhesion, and the same effect was observed for the melt strength and breaking stretching ratios. Mechanical properties, including the elastic modulus, tensile strength and elongation at break, improved in both types of samples but more significantly in the fibers. These improvements were attributed to the orientation of the matrix, the formation of PET microfibrils, and the reduction in the size of graphene nanoparticles due to the action of the elongational flow. This reduction, facilitated by the elongation flow and the action of the compatibilizer, improved matrix-nanofiller adhesion due to the increased contact area between the two polymeric phases and between the filler and matrix. Finally, a transition from brittle to ductile behaviour was observed, particularly in the system with the compatibilizer, attributed to defect reduction and improved stress transmission.

A Vitrimer Acts as a Compatibilizer for Polyethylene and Polypropylene Blends.

Polymer compatibilization plays a critical role in achieving polymer blends with favorable mechanical properties and enabling efficient recycling of mixed plastic wastes. Nonetheless, traditional compatibilization methods often require tailored designs based on the specific chemical compositions of the blends. In this study, we propose a new approach for compatibilizing polymer blends using a dynamically crosslinked polymer network, known as vitrimers. By adding a relatively small amount (1-5 w/w%) of a vitrimer made of siloxane-crosslinked high-density polyethylene (HDPE), we successfully compatibilized unmodified HDPE and isotactic polypropylene (iPP). The vitrimer-compatibilized blend exhibited enhanced elongation at break (120 %) and smaller iPP domain sizes (0.4 μm) compared to the control blend (22 % elongation at break, 0.9 μm iPP droplet size). Moreover, the vitrimer-compatibilized blend showed significantly improved microphase stability during annealing at 180 °C. This straightforward method shows promise for applications across various polymer blend systems.

A Vitrimer Acts as a Compatibilizer for Polyethylene and Polypropylene Blends

AbstractPolymer compatibilization plays a critical role in achieving polymer blends with favorable mechanical properties and enabling efficient recycling of mixed plastic wastes. Nonetheless, traditional compatibilization methods often require tailored designs based on the specific chemical compositions of the blends. In this study, we propose a new approach for compatibilizing polymer blends using a dynamically crosslinked polymer network, known as vitrimers. By adding a relatively small amount (1–5 w/w%) of a vitrimer made of siloxane‐crosslinked high‐density polyethylene (HDPE), we successfully compatibilized unmodified HDPE and isotactic polypropylene (iPP). The vitrimer‐compatibilized blend exhibited enhanced elongation at break (120 %) and smaller iPP domain sizes (0.4 μm) compared to the control blend (22 % elongation at break, 0.9 μm iPP droplet size). Moreover, the vitrimer‐compatibilized blend showed significantly improved microphase stability during annealing at 180 °C. This straightforward method shows promise for applications across various polymer blend systems.

Morphological analysis of mechanically recycled blends of high density polyethylene and polypropylene with strong difference in melt flow index

Polyolefin (PO) blends are difficult to separate due to density and chemical structure similarities. The associated waste treatment in the context of mechanical recycling is therefore complicated by the establishment of multi-phase morphologies that are not yet fully understood. In the present work, a high density polyethylene (HDPE) with a very high melt flow index (MFI) and a polypropylene (PP) with a very low MFI are deliberately mingled to better understand the full spectrum of morphological variations for PO blending. The linkage with the control over injection mold-based mechanical properties such as tensile strength, elasticity modulus, elongation at break, and impact strength is made. This is done supported by the connecting of experimental analyses at different scales, including (i) the molecular scale via size exclusion chromatography and Fourier transform infrared spectroscopy (FTIR), and (ii) the meso-scale via scanning electron and polarized light microscopy as well as differential scanning calorimetry, including a differentiation between the bulk and surface region. Emphasis is both on blends processed once and re-processed either once, twice or three times. For the single processing, it is demonstrated that in most cases a droplet morphology is obtained, with smaller droplets in case HDPE is the minor component and with a dominance of HDPE at the surface even for 60% PP, due to a better HDPE flowability. It is further shown that the scission of PP chains and crosslinking of HDPE chains respectively facilitates and inhibits crystallization, at least if meso-scale -mixing as more evident during re-processing is not taking over. It is also highlighted that the properties of PP can be enhanced by adding up to 10 wt% HDPE, acting as a filler, and that the (ideally) reprocessed blends remain suitable for application.