Polypropylene Chains Research Articles

Facile Construction of Polypropylene Foam with Dense Oriented Cell Structure and Enhancing-ductility Mechanism

Common polypropylene (PP) foam exhibited intrinsic inferior ductility and mechanical strength, which restricted its application as lightweight structural parts. To improve the ductility and mechanical strength of PP foam, the highly oriented PP component with fibrillar structure (cold-drawn fiber, CDF) was blended with isotropic PP resin to prepare PP/CDF foam via a facile foam injection molding process. During foaming at 170°C, CDF was not melted completely. Then, the remaining fibrils acted as shish structure and induced the crystallization of PP chains on its surface to form oriented kebab crystals, and the viscoelasticity and melt strength of the system were significantly improved, which promoted the nucleation of the bubble and the elongation of the cells, constructing a dense oriented cell structure with a large number of slender cylindrical cell walls for the foam. Such cell wall structure was prone to large plastic deformation and continuous elongation under load, which reduced stress concentration and absorbed a significant amount of tensile energy. As a result, a ductile and strong PP/CDF foam was successfully constructed, which exhibited roughly 465% increase in strain at break and 15% increase in tensile strength, respectively compared with PP foam.

Absorption of Polypropylene in Dipalmitoylphosphatidylcholine Membranes: The Role of Molecular Weight and Initial Configuration of Polymer Chains.

We study by molecular dynamics simulations the absorption of polypropylene (PP) chains within a dipalmitoylphosphatidylcholine (DPPC) lipid membrane in aqueous solvent. DPPC represents the most abundant phospholipid in biological membranes, while PP is one of the most common synthetic polymers diffused in the anthropic environment. By following in detail the absorption process, and the corresponding structural modification undergone by the membrane, we show how the initial configuration and the PP molecular weight determine the overall behavior of the system. Specifically, if PP chains initially lie on the DPPC surface, they are fully absorbed; likewise, polymers initially included within the membrane cannot escape from. On the other hand, if polymers are placed sufficiently apart from the membrane, they have time to join together and coalesce into a few nanoparticles. At contact, such nanoparticles may completely dissolve (for low molecular weight) and then be absorbed. For high molecular weight, not all of them dissolve, and therefore the system attains a condition in which some of the chains are absorbed, while others form a residual nanoparticle staying outside (but in contact with) the membrane. Such a state─albeit energetically unfavorable with respect to a condition in which all PP chains are absorbed─remains stable, at the least over a substantial simulation time, extending in our study up to 1.6 μs. The tendency for polymers to spontaneously form aggregates, which then prefer to stay in contact with the membrane, is further corroborated by calculation of the DPPC-nanoparticle potential of mean force.

Molding blends of silicone polymer / polypropylene with durable resistant to extreme conditions based on migration and compatibility of molecular chains

Because of low surface energy, silicone polymers would easily peel off from polypropylene (PP) substrate as hydrophobic coatings and they are incompatible with PP in melt-blending process as well. Therefore, ethylene polymers modified with both silicone and alkane side-groups were prepared by nucleophilic substitution in this work. It was confirmed that these prepared polymers could migrate and aggregate to the surface of the blends at that melting temperature when blended with PP due to the low surface energy and high entropy of silicone side groups. Meanwhile, chain entanglement was achieved between alky side-groups of silicone polymers and polymer chain of PP by melt-blending process, so that the compatibility of the blends was improved and the bonding force of two polymers increased simultaneously. Accordingly, molding blends with stable and durable hydrophobility were successfully gained based on migration of silicone and entanglement of alkane and PP. It’s noticeable that the water contact angle of the blend remained to be about 106° from 113°, even soaking in acid (pH = 1) and alkali (pH = 14) solutions, deionized water and anhydrous ethanol, or under multiple strong frictions. This will provide a facile and effective strategy to endow general materials with durable antifouling properties directly by injection molding without additional coating.

Quasi-Hydrogen Bond and Charge-Trapping Effect Originating from Polar Side Group Lead to Significantly Suppressed Charge Transport in Polypropylene.

How to fundamentally suppress charge transport is one of the essential issues in polymer dielectrics. This work reports significant charge transport suppression by glycidyl methacrylate (GMA) side group modification on polypropylene (PP). Experimental and computational investigations discover for the first time a quasi-hydrogen bond effect generated by carbonyl and epoxide of GMA in PP inter/intramolecular structure, while introducing trap energy levels within the HOMO-LUMO gap. These energy levels suppress the leakage current of GMA-modified PP thanks to the charge-trapping effect. The quasi-hydrogen bond originating from the interaction between the high-polar GMA group and flexible PP chain raises the thermostability while averaging the electron distribution between hydrogen and acceptor oxygen, which is conducive to lessening electric weak points, suppressing charge transport, and finally enhancing the electrical breakdown strength. This work provides new thinking on polymer dielectric design and charge transport regulation utilizing electron structure and weak interaction at the molecular scale.

Impact of organic peroxide on a moderate molecular weight homo-polypropylene vis breaking, and mechanism of interaction

In this study, we show that organic peroxide is a useful tool for breaking the viscosity or chain of polypropylene during melt processing to provide a regulated rheology product. Reactive extrusion is used to crosslink peroxide and combine it with polypropylene (PP). To achieve end-use applications with performance targets, stabilizers are required to preserve the polymer’s initial strength, flexibility, and toughness properties. Other additives are added to PP in addition to stabilization in order to enhance or change certain of its properties. With the addition of varying levels of organic peroxide [2,5-Dimethyl-2,5-di (tert-butyl peroxy) hexane]. The use of peroxide in the manufacturing process of polypropylene is a method of breaking in the polymer chains, which can affect its properties, including its MFI. It is possible that increasing the amount of peroxide used leads to a higher degree of branching or cross-linking, which in turn leads to a higher MFI value. However, it is important to note that the relationship between the amount of peroxide used and the resulting MFI values may not be linear and may depend on other factors as well. In addition to the MFI, other properties of the polypropylene were also measured, including shear and melt flow index, melting and crystallization temperatures, flexural and tensile moduli, and yield stress. These properties are important for understanding the mechanical and thermal behavior of the polymer and can be used to optimize its performance for specific applications.

Optimization of malic anhydrate concentration in manufacturing PP-g-MA compatibilizer on test percent of grafting degree

The difference in polarity means that two or more materials cannot react, a connecting material such as a compatibilizer is needed to react between polar and non-polar materials. This research aims to determine the effect of maleic anhydride (MA) concentration on the process of grafting MA onto polypropylene (PP) chains with the help of benzoyl peroxide (BPO) as an initiator. The method used to mix these two materials uses the blending method using an internal mixer instrument and testing the percent degree of grafting using the titration method with three repetitions of the test.The research results showed that the highest percent grafting degree occurred at a concentration of 86% PP, 11% MA, and 3% BPO, with a value of 10.28%. The Spectroscopy Fourier Transform Infrared (FTIR) analysis of Polypropylene grafted maleic anhydride (PP-g-MA) showed the presence of new peaks at wavenumbers 1707cm-1 and 1162 cm-1.Increasing the concentration of maleic anhydride had no effect on increasing the percent degree of grafting.

Scalable chlorination of polypropylene for structural modification and flame retardancy as coating materials of insulation cable

ABSTRACT Chemical precipitation route has been demonstrated for in-situ chlorination of polypropylene and structural modification to integrate flame retardancy along with facile processing parameters, i.e. optimum melt flow index and mechanical properties. Thus, obtained chlorinated polypropylene (Cl-PP) was characterized for optimized composition and degree of chlorination, chemical structure, morphology, physical properties with the help of infra-red spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), melt flow index and other standard methods. The analytical results revealed the 74% chlorination of polypropylene chain increased with the molecular weight, comparable melt flow index and improved flame retardancy from V2 to V0 grade on UL-94 scale due to reduced heat release rate and improved limiting oxygen index from 17.5 to 27.1 due to structural changes and induced polycrystallinity. The evolved features of PP were explained on the basis of synergistic interaction, evolved crystallinity, size reduction and functionality during chemical treatments and reprecipitations. Further, the obtained Cl-PP was explored as the coating material for insulation of cables with electric insulation and durable properties.

Post-polymerization modification of polypropylene with different functional groups utilizing non-catalytic C–H insertion of sulfonyl azide

This study presents a comprehensive investigation into the preparation of functionalized polypropylene (PP) with different functional groups, such as amino-, hydroxyl-, acetamido-, and carboxyl-groups, utilizing efficient C–H insertion capability of sulfonyl azide (SA) compounds with the functional groups. The reactive melt mixing of PP and the SA compounds was performed at temperatures determined by the decomposition temperatures of the SA groups, followed by purification processes to remove unreacted SA compounds, confirming the establishment of stable covalent linkages between the SA compounds and PP chains. Grafting efficiency (GE) values were determined using FT-IR spectroscopy, showcasing efficient grafting of the SA compounds onto PP chains with GE values ranging from 60 % to 70 %. Remarkably, SA compound with carboxyl functional group exhibited an exceptionally high GE value of ∼90 %, likely attributed to its electron-withdrawing carbonyl group. XRD analyses, thermal analyses, morphological analyses of cryogenically fractured modified PPs and mechanical property analyses revealed successful incorporation of SA compounds into PP chains with relatively low sensitivity of the crystal structure of the modified PPs to the incorporated SA compounds. Hydrophilicity assessments revealed improved paint adhesion capabilities of the modified PP surfaces, highlighting the potential for the tailored surface modification strategies to enhance material characteristics.

Thermal behavior of polypropylene composites with segregated graphene nanoplatelet network

AbstractThree‐dimensional architecture of segregated network can significantly influence thermal behaviors of polymer composites, such as the melting temperature (Tm) and degradation temperature. However, there have been few systematic studies on the thermal behaviors of polypropylene (PP) composites with a segregated network that the fillers were selectively located in the polymeric particle interfaces. In this study, we found that introduction of the segregated graphene nanoplatelet (GNP) network induced the maximum Tm of 177.6°C, extending the operating temperature by 11.5°C compared to the Tm of composites with randomly dispersed GNPs. In contrast, the thermal degradation temperature of polymer composites varied insignificantly regardless of introduction of the segregated network because the thermal degradation of the polymer matrix occurred after the PP chains melted and the segregated GNP network collapsed at temperatures above the Tm. Therefore, the incorporation of a segregated network can be an effective option for enhancing the Tm and extending the operating temperature of the polymer composites.Highlights Segregated network induced the remarkable increase in melting temperature. Meanwhile, the segregated network had little effect on decomposition temperature. Segregated composite was efficient strategy for expanding operating temperature.

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.

Kinetics in high-temperature free-radical reactive processing: Grafting maleic anhydride onto polypropylene in the presence of nanoclay-supported peroxide

The kinetics of grafting and chain scission reactions during maleic anhydride (MA) grafting onto polypropylene (PP) using nanoclay-supported peroxide (o-MMT/DCP) in the molten state were evaluated through the development of a new methodology. A combination of characterization techniques and mathematical data manipulation was employed for this assessment. To inhibit radical propagation and recombination, tetramethylpiperidine-1-oxyl (TEMPO) was used as a free radical scavenger. Rheological stability tests demonstrated that TEMPO was more effective as a reaction inhibitor. The kinetics dataindicated that the use of o-MMT/DCP resulted in products with higher MA grafted levels and molecular weight (MW) compared to grafting performed in the absence of o-MMT. Additionally, some changes in molecular architecture were observed. The chain scission distribution function (CSDF) revealed that during the MA grafting process, the molecular weight of PP was reduced through chain scission, with a preference for longer chains. Furthermore, the presence of o-MMT was found to restrain the level of PP chain scission, likely due to recombination on the clay surface.

Identification of plastic-degrading bacteria in the human gut

Environmental pollution caused by the excessive use of plastics has resulted in the inflow of microplastics into the human body. However, the effects of microplastics on the human gut microbiota still need to be better understood. To determine whether plastic-degrading bacteria exist in the human gut, we collected the feces of six human individuals, did enrichment cultures and screened for bacterial species with a low-density polyethylene (LDPE) or polypropylene (PP)-degrading activity using a micro-spray method. We successfully isolated four bacterial species with an LDPE-degrading activity and three with a PP-degrading activity. Notably, all bacterial species identified with an LDPE or PP-degrading activity were opportunistic pathogens. We analyzed the microbial degradation of the LDPE or PP surface using scanning electron microscopy and confirmed that each bacterial species caused the physical changes. Chemical structural changes were further investigated using X-ray photoelectron spectroscopy and Fourier-transform-infrared spectroscopy, confirming the oxidation of the LDPE or PP surface with the formation of carbonyl groups (C=O), ester groups (CO), and hydroxyl groups (-OH) by each bacterial species. Finally, high temperature gel permeation chromatography (HT-GPC) analysis showed that these bacterial species performed to a limited extent depolymerization. These results indicate that, as a single species, these opportunistic pathogens in the human gut have a complete set of enzymes and other components required to initiate the oxidation of the carbon chains of LDPE or PP and to degrade them. Furthermore, these findings suggest that these bacterial species can potentially biodegrade and metabolize microplastics in the human gut.

Research progress on the flame retardation and modification of polypropylene by montmorillonite

Montmorillonite can be used to achieve nano-dispersion level by forming peel or intercalation structure in polypropylene body, so as to improve the mechanical properties of the material. In addition, montmorillonite plays the role of nucleating agent during the crystallization of polypropylene, which improves the crystallization efficiency of polypropylene. After the organic modification of montmorillonite, the spacing between crystal surfaces can be enlarged to form organic montmorillonite, which makes the molecular chains of polypropylene more easily dispersed to the interlayer of organic montmorillonite, forming a dense surface layer in the process of thermal decomposition, so as to improve the thermal stability of polypropylene and enhance the flame retardant property of polypropylene. Many previous studies have shown that montmorillonite plays a significant role in improving the mechanical strength and crystallization effect of polypropylene, as well as the flame retardant properties of nanocomposites.

Shear relaxation behavior for degraded polypropylene melt in torque rheometer

AbstractShear relaxation behavior for polymer melt exists in different processing techniques and influences the dimensional accuracy and production efficiency of polymer products. A micro physical and mathematical model based on microstructure of polymer chains and processing parameters was established and verified by experimental results obtained from a torque rheometer. The shear relaxation time of polypropylene degraded by di‐tert‐butyl peroxide was characterized with torque rheometer. The effects of microstructure and processing parameters on the shear relaxation time was investigated. The results showed that a wider molecular weight distribution could result in a decrease in shear relaxation time and polypropylene chains with higher molecular weight were more sensitive to molecular weight distribution. The shear relaxation time declined exponentially with shear rate and increased with internal pressure. The temperature could enhance the movement of polymer chains and reduce the shear relaxation time linearly, but polypropylene with lower molecular weight was less sensitive to temperature. The insight obtained from the mathematical and experimental results can be profoundly applied in practical process control to manufacture product with better dimensional stability and production efficiency for viscoelastic polymer.Highlights A physical and mathematical model based on microstructure and processing parameters of molecular chains was established to explore the shear relaxation mechanism. Shear relaxation time of polypropylene degraded by di‐tert‐butyl peroxide was characterized with the help of torque rheometer. The effects of microstructure and processing parameters on shear relaxation time was investigated to optimize the manufacturing of polypropylene products.

Compatibilization of Immiscible Polypropylene/Poly(methyl methacrylate) Blends by Silica Particles with Janus and Random Component-Selective Grafts.

Introducing component-selective polymer chains onto the surface of a particle is an effective approach to improve the compatibilization efficiency of a particle-based compatibilizer. In this study, two particles with different kinds of component-selective polymer chains that have the same length and similar density but different graft locations were synthesized and their compatibilization effects were comparatively investigated. It was found that compared with the particle with homogeneous PMMA and PP grafts (R-P), the particle with a hemisphere of poly(methyl methacrylate) (PMMA) grafts and other hemisphere of polypropylene (PP) chains (J-P) showed a better compatibilization effect under equal loadings, although both particles exhibited high efficiency. The better compatibilization effect of particles with Janus grafts may be attributed to the stronger entanglements between grafted polymer chains and selective individual components. This work suggests that optimizing the graft location of a particle is an effective strategy for improving its compatibilization efficiency and helpful for the design of advanced particle compatibilizers.

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.

Effect of Copper Antifouling Paint on Marine Degradation of Polypropylene: Uneven Distribution of Microdebris between Nagasaki Port and Goto Island, Japan.

Microplastics (MP) encompass not only plastic products but also paint particles. Marine microdebris, including MP, was retrieved from five sampling stations spanning Nagasaki-Goto island and was classified into six types, primarily consisting of MP (A), Si-based (B), and Cu-based (C) paint particles. Type-A particles, i.e., MP, were exceedingly small, with 74% of them having a long diameter of 25 µm or less. The vertical distribution of type C, containing cuprous oxide, exhibited no depth dependence, with its dominant size being less than 7 μm. It was considered that the presence of type C was associated with a natural phenomenon of MP loss. To clarify this, polypropylene (PP) samples containing cuprous oxide were prepared, and their accelerated degradation behavior was studied using a novel enhanced degradation method employing a sulfate ion radical as an initiator. Infrared spectroscopy revealed the formation of a copper soap compound in seawater. Scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis indicated that the chemical reactions between Cl- and cuprous oxide produced Cu+ ions. The acceleration of degradation induced by the copper soap formed was studied through the changes in the number of PP chain scissions, revealing that the presence of type-C accelerated MP degradation.

Theoretical Prediction of the Reaction Probabilities of H, O, and OH Radicals on the Polypropylene Surface.

To determine the H-abstraction reaction probabilities of H/O/OH radicals with a polypropylene (PP) surface, a first-principles calculation was performed based on the DLPNO-CCSD(T)/CBS//M06-2X-D3/def-TZVP theory level. The PP chain model used in this study was 2,4,6-trimethylheptane. The rate constants of the H/O/OH radicals with the isolated PP chain model were calculated based on the conventional transition-state theory. By comparing the experimental values and considering the error factors and their compensation, it was concluded that the orders of magnitude of the predicted rate constants were accurate. The resulting rate constants were converted to reaction probabilities between the H/O/OH radicals and the PP surface. The method used in this study is applicable for obtaining theoretical values of surface reaction probabilities based on first-principles calculations. The calculation at the DLPNO-CCSD(T)/CBS theory level has high accuracy but consumes a large amount of computational resources. The study also demonstrated that the double-hybrid functionals, wB97x-2-D3(BJ) and rev-DSD-PBEP86-D3(BJ), with a 3-ζ or 4-ζ basis set, could reproduce the electronic energy values obtained from DLPNO-CCSD(T)/CBS while using only approximately 1/100 of the computational resources required by the latter under our computer configuration.

Revealing the pyrolysis mechanism of polypropylene cable insulation: A combined study of TG‐GC experiments and RMD/DFT simulations

AbstractStyrene grafted polypropylene (PP‐g‐St) is one of the insulating materials for high voltage power cables. However, the process of pyrolysis gas generation in polypropylene cable insulation remains poorly understood. To address this knowledge gap, this study employed a combination of thermogravimetric‐gas chromatography experiments, density functional theory, and reactive molecular dynamics simulations. The experimental findings revealed that the pyrolysis gases primarily consisted of H2, CO, C2H4, and CH4. Higher temperatures were found to increase the yields of H2 and CO. The simulation results indicated that H2 and CO were generated through the rupture of less reactive olefins and radicals, while C2H4 was primarily produced by the rupture of CC bonds in the polypropylene chain. Additionally, CH4 was formed when CH3 groups captured hydrogen from other molecules. By the chain reaction mechanism, we enable the calculation of the activation energy of PP‐g‐St. This study provides a theoretical foundation for understanding the pyrolysis gas generation.

Theoretical mechanism behind the higher efficiency of O than OH radicals in polypropylene surface modification: a molecular dynamics study

O and OH radicals are the most important reactive oxygen species in the plasma treatment of polymer surfaces. In our previous studies, we found that the modification efficiency of polypropylene (PP) surface by O radicals was approximately four times higher than that by OH radicals. This observation contrasts with the well-established fact that the chemical reactivity of O radicals with saturated hydrocarbons (C n H2(n + 1)) is 50–60 times lower than that of OH radicals. In this study, classical molecular dynamics simulations with a reactive force field were used to explain this contradiction. The results showed that the surface modification of PP by O or OH radicals is a Langmuir–Hinshelwood process. Both O and OH radicals penetrated the bulk PP, that is, physical adsorption occurred before the chemical reactions. The penetration depth of O radicals was greater than that of OH radicals. Compared to the case of OH radicals, alkoxy radicals (RO·) are more readily formed upon the interactions of the PP surface with O radicals. Furthermore, the β-scission (splitting of the C–C bonds) of RO· can be accelerated by the physically adsorbed O radicals, leading to earlier breakage of PP chains. The improved efficiency of the surface modification of PP upon exposure to O radicals, in contrast to that of OH radicals, can be attributed to the differences in the above three crucial processes. These findings are significant for modelling and understanding the mechanisms of plasma-polymer surface treatment at the atomic and molecular levels.