Impact Polypropylene Copolymer Research Articles

Largely Improved Creep Resistance and Thermal-Aging Stability of Eco-Friendly Polypropylene High-Voltage Insulation by Long-Chain Branch-Induced Interfacial Constraints.

Polypropylene (PP)-based composites have attracted numerous attention as a replacement of prevailing cross-linked polyethylene (XLPE) for high-voltage insulation due to their ease of processing, recyclability, and excellent electrical performance. However, the poor resistances against high-temperature creep and thermal aging are obstacles to practical applications of PP-based thermoplastic high-voltage insulation. To address these problems, in this Letter, we synthesized an impact polypropylene copolymer (IPC) containing multifold long-chain branched (LCB) structures in phases, especially the interfaces between the PP matrix and the rubber phase. The results indicated that the structural stability of LCBIPC was significantly enhanced under extreme conditions. In comparison to IPC (without LCB structures), 24.1% less creep strain and 75.2% less unrecoverable deformation are achieved in LCBIPC at 90 °C. In addition, the thermal aging experiments were performed at 135 °C for 48 and 88 days for IPC and LCBIPC, respectively. The results show that the resistance against thermal aging was also enhanced in LCBIPC, which showed a 133% longer thermal aging life compared to IPC. Further results revealed that the interfacial layer between the PP matrix and the rubber phase was constructed in LCBIPC. The two phases are tightly linked by chemical bonds in LCB structures, leading to enforced constraints of the rubber phase at the micro level and better resistance performance against creep and thermal aging at the macro level. Evidently, the reported eco-friendly LCBIPC thermoplastic insulation shows great potential for applications in high-voltage cable insulation.

Simultaneous Promotion of the Mechanical Flexibility and Dielectric Strength of Impact Polypropylene Copolymers Containing Multifold H-Shape Long-Chain-Branching Structures for Recyclable Power Cable Insulation Application

Simultaneous Promotion of the Mechanical Flexibility and Dielectric Strength of Impact Polypropylene Copolymers Containing Multifold H-Shape Long-Chain-Branching Structures for Recyclable Power Cable Insulation Application

Phase morphology of nascent impact polypropylene copolymer and its evolution in the melt

In this study, the morphology of the nascent grains of a commercial impact polypropylene copolymer (IPC) and its evolution upon melting was investigated by atomic force microscopy (AFM) and atomic force microscopy-infrared (AFM-IR). The grains were found to be heterogeneous, about half translucent and the rest opaque, containing 12.2 and 2.0 wt% ethylene comonomer, respectively. The ethylene-propylene (EP) rubber in these two kinds of grains differed in content, but was of the same composition, filling the voids between isotactic polypropylene (iPP) subglobules in irregular long strips. Upon melting, the EP rubber strips were found to quickly break into smaller sections, and their shape became more regular, within which rigid cores started to appear. Then, disperse particles with clear core-shell structure were observed, and they grew slightly bigger at longer heating time. Both translucent and opaque grains went through the same morphology evolution process, resulting in core-shell particles of the same phase compositions as assessed by AFM-IR analysis. In addition, the translucent grains were mixed with 5 wt% of a deuterated PP in a twin-screw extruder, and the blend pellet was examined by AFM-IR, and the results showed that the deuterated species was abundant in the PP matrix and totally absent within the disperse particles, implying no encapsulation of the molecules from the matrix surrounding in the formation of the core-shell structure in the melt processing.

Promoting the strength of Impact Copolymer Polypropylene (ICP) via innovative compounding approaches

Promoting the strength of Impact Copolymer Polypropylene (ICP) via innovative compounding approaches

Multilayered Core–Shell Structure in an Impact Polypropylene Copolymer Investigated by Atomic Force Microscopy–Infrared

Multilayered Core–Shell Structure in an Impact Polypropylene Copolymer Investigated by Atomic Force Microscopy–Infrared

Morphology of impact polypropylene copolymer extruded cast film revealed by confocal Raman imaging.

An impact polypropylene copolymer (IPC), composed of polypropylene (PP) and ethylene-propylene copolymer (EPC), was synthesized through two-stage in-reactor polymerization. A systematic investigation of the crystalline structure, thermal behavior, morphology, and tensile properties of the IPC extruded cast film was conducted. Specifically, the morphology of EPC was obtained by confocal Raman imaging by depicting the spatial distribution of the Raman band located at 1064 cm-1. The EPC phase exhibits fibrous morphology with the long axis aligning along the machine direction (MD). A three-dimensional (3D) heterogeneous structure of the IPC cast film obtained by confocal Raman imaging confirms that the fibrous EPC phase is dispersed in a 3D framework of the PP matrix. The mesomorphic phase in the as-prepared cast film transforms to a stable α-form crystal after annealing at 130 °C, which improves the yield strength but decreases the elongation of the cast film. The WAXD and SAXS results indicate that there is no obvious orientation of the crystallites. Thus, the anisotropy of tensile properties in the MD and transverse directions is closely related to the anisotropic phase morphology at the micrometer scale. The results reveal that the mechanical performances of IPC films are determined by the crystalline structure of the PP matrix and the morphology.

Degradation indicators in multiple recycling processing loops of impact polypropylene and high density polyethylene

In a circular economy, polymeric materials are used in consecutive loops to convert by-products of one application to a valuable product for another. This reprocessing, however, entails degradation processes in the polymers, which manifest as changes in the material properties. This study looks at the impact of several closed recycling loops on the material properties of two different polyolefins: Polypropylene impact copolymer (PPc) and High Density Polyethylene (HDPE). Relationships between polymer chemical features and processing behavior were sought. The samples were characterized using melt flow index (MFI), in-line capillary rheometry, infrared spectroscopy, differential thermal analysis (DSC), thermogravimetric analysis (TGA) and mechanical tensile testing. The polyolefins processability and process stability, on the other hand, was assessed in through injection molding parameters monitoring. Though evidences of chain scission for PPc and chain branching for HDPE were found, the examined polyolefins revealed low damage to mechanical properties and the possibility for future industrial reemployment at least up to 3 consecutive processing loops for both polymers.

Effect of the multiple injection process on the structural and mechanical properties of PP impact copolymers focusing on the deformation of ethylene-propylene copolymer

The influence of multiple injection on the structural and mechanical properties of PP impact copolymers (ICP) has been investigated, mainly focusing on the deformation of dispersed ethylene-propylene copolymer (EPC) particles in ICPs. Various properties of recycled ICPs throughout repetitive injection processes have been compared. The thermo-mechanical degradation by heat and shear stress imposed on ICPs several times via multiple injection triggered chemical changes, such as the generation of CC and CO bonds and chain scission in ICPs. These changes alter the crystallinity of the ICPs by shortening the chain length and narrowing the molecular weight distribution. To determine the effect of multiple injection on the deformation of EPC particles, the intrinsic viscosities (IV) of the polypropylene (PP) matrix and dispersed EPC were measured. Degradation by multiple injection was greater for PP than for EPC, thereby increasing the viscosity ratio (IVEPC/IVPP). At a high viscosity ratio, the PP matrix could not effectively transfer shear stress to the dispersed EPC particles, causing the EPC particles to agglomerate and become larger with poor dispersity. Regarding the mechanical properties, the agglomeration of EPC exerted a significant negative effect on the Izod impact strength. Finally, numerical calculations in the injection mold flow region confirmed that the re-injected product required a higher shear stress than the virgin product.

Assessing the environmental impact due to photolytic degradation of ethane-bis(pentabromophenyl) in plastics

Photolytic degradation of brominated flame retardants is one of the potential decomposition pathways in the environment, and for some flame retardants such as ethane-bis(pentabromophenyl) (EBP), also called decabromodiphenyl ethane, there are concerns that degradation products may be harmful. In this paper, we present photolytic studies of EBP in high-impact polystyrene (HIPS) and polypropylene impact copolymer (PP) using accelerated weatherometry. The half-life of photolytic debromination of EBP in HIPS was estimated to be more than 200 years, which can be contrasted with half-lives of minutes for photolysis conducted on dilute EBP solutions. Perhaps more importantly, there was no subsequent debromination to the octabrominated congeners or lower. No evidence of debromination was seen in PP, which confirms the importance of matrix effects. We also saw no evidence of accelerated resin photooxidation caused by EBP. These studies demonstrate that EBP is much more photolytically stable in resins than structurally-similar decabromodiphenyl ether, and a read-across comparison between the two flame retardant molecules for this degradation pathway is misleading.

Enhancement in Electrical Properties of Impact Polypropylene Copolymer for Cable Insulation Induced by Rapid Cooling

Impact polypropylene copolymer (IPC) is a promising eco-friendly power cable insulating material with great potential to replace the thermosetting cross-linked polyethylene (XLPE). This article compares the breakdown strength and water tree resistance of IPC and isotactic polypropylene (iPP) after different cooling rates. Unexpectedly, an abnormal enhancement of IPC’s insulating property is discovered. The breakdown strength and water tree resistance of IPC are both increased after rapid cooling, which is opposite to the electrical property deterioration generally found on iPP and XLPE with similar treatment. To reveal the mechanism of abnormal enhancement of IPC, the crystalline structure, phase morphology, and trap distribution are characterized. The results indicate that rapid cooling induces an abnormal increase in the crystallinity of IPC due to the formation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> crystals, which in turn increases the deep trap level and density and leads to enhanced breakdown strength. Moreover, the formation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> crystal can also enhance the inter-lamellar coupling and result in higher tensile yield strength, further, decreasing the water tree initiation probability. These results reveal that rapid cooling can significantly regulate the performance of IPC, which should be given serious consideration for the application of IPC in cable insulation.

Reactive Compatibilization of Impact Copolymer Polypropylene and Organically Modified Mesoporous Silica to Prepare Composites Possessing Enhanced Mechanical Properties

Mesoporous silica was evaluated as functionalized filler in impact copolymer polypropylene (ICP) in its original form as well as after organic modification. Mesoporous silica was synthesized by base-catalyzed hydrolysis of tetraethyl orthosilicate in the water–acetone medium. The organic modification of mesoporous silica was carried out using commercially available silane with a terminal unsaturated bond and by synthesizing silane precursor by chemical treatment via TEMPO-initiated thiol–ene chemistry to introduce alkyl chains terminating in hydroxyl groups. The characterization for all types of mesoporous silica prepared was done using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), solid-state nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) analysis, X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). ICP–mesoporous silica composites were prepared using 1, 5, and 10 phr mesoporous silica and organically modified mesoporous silica loading via reactive compatibilization and were tested for their thermal, morphological, rheological, and mechanical properties. The addition of mesoporous and organically modified mesoporous silica enhanced thermal stability and nucleation with respect to neat ICP. Tensile and flexural moduli were improved while maintaining their impact strength. Analysis of rheological properties revealed a rise in zero-shear rate viscosity in ICP–mesoporous silica composites. DMA studies showed higher storage and loss modulus with the addition of mesoporous silica in ICP.

Impact polypropylene copolymers containing multifold H-shape long-chain-branching structures: Effect on dielectric and electrical properties

This paper discusses the dielectric and electrical properties of novel impact polypropylene copolymers containing multifold H-shape long-chain-branching structures (LCB-IPCs), i.e. PP-H-PP, PP-H-EPC (EP copolymer), and EPC-H-EPC. Dielectric spectroscopy study indicates that the LCB structures tend to decrease the dielectric constant of IPC increased from that of net PP due to EPC alloying. Electron trap distribution study reveals that the LCB structures have the effect of deepening the electron traps of IPC shallowed from those of net PP by EPC alloying. Similar effect of LCB structures extends to electrical breakdown properties. Compared to LCB structure-free pristine IPC, which is reduced on electrical breakdown strength under both AC and DC electrical voltage as compared to net PP, LCB-IPCs are on the contrary measured continuously increased breakdown strengths in both occasions. The improvements in electrical properties of LCB-IPCs are mainly attributed to the crystalline morphology alterations, i.e. decreasing in spherulite size and increasing in spherilite density, due to PP-H-PP structure exercising effective nucleation for PP crystallization.

Comprehensive Comparisons of Grafting-Modified Different Polypropylene as HVDC Cable Insulation Material

Polypropylene (PP) is considered to be a rather potential material for recyclable HVDC cable insulation. Grafting modification has been proven to be effective to further enhance the dielectric properties of PP. To investigate the grafting effect on the performance of different PPs, homopolymerized PP (PPH), ethylene-propylene copolymer (PEC), and impact PP copolymer (IPC) are, respectively, grafting-modified by styrene, and the comprehensive properties are experimentally studied. The results indicate that all these grafting-modified PPs show enhanced dielectric properties, while the enhancement levels differ. Styrene-grafted PPH presents the best dielectric properties improvement and highest thermostability, but the elastic modulus is also the highest. PEC exhibits moderate dielectric properties enhancement after grafting modification. Grafting-modified IPC shows excellent mechanical properties, but the enhancements on dielectric properties are rather limited. Grafting styrene has no significant influence on the thermal and mechanical properties of PP. In conclusion, PPH is preferred to be the matrix for styrene-grafting to achieve enhanced dielectric properties. However, the mechanical properties still need further modification to meet the demands of cable insulation.

The Impact of Reprocessing with a Quad Screw Extruder on the Degradation of Polypropylene.

During mechanical recycling, polypropylene typically is reprocessed using a single- or twin-screw extruder. The degradation of polypropylene during this reprocessing reduces the polymer’s molecular weight and, consequently, limits the performance of the recycled resin. This work investigated the impact of a quad screw extruder (QSE), which has greater free volume, on the reprocessing of an impact copolymer polypropylene. To mimic the recycling process, the polypropylene was subjected to three processing cycles using a QSE and a comparable twin-screw extruder (TSE) operated at three screw speeds. The reprocessed materials were characterized for their rheological, morphological, and mechanical properties. For both extruders, increasing the number of reprocessing cycles and the screw speed resulted in higher melt flow indices, decreases in zero-shear viscosity, and shifting of the crossover points for the storage and loss moduli, which indicate reductions in the molecular weight and narrowing of the molecular weight distribution of the polypropylene. The QSE exhibited greater reductions in molecular weight compared to the TSE, probably due to the higher stresses associated with the three intermeshing points along its screws. Reprocessing caused a significant reductions in the Izod impact strength of the reprocessed polypropylene, which correlated with reductions in the particle size and particle size distribution of the dispersed rubbery phase in the polypropylene during reprocessing.

Impact polypropylene copolymers containing multifold H-shape long-chain-branching structures: Synthesis and properties

ω -Alkenylmethyldichlorosilane as a proven in-situ long-chain-branching agent particularly effective with olefin polymerization by Ziegler-Natta catalysts was seamlessly fit into fully implemented impact copolymerization of propylene exercised by polymerization, steam-treatment of afforded polymer granules, and twin-screw extrusion in a row to deliver, for the first time, long-chain-branched impact polypropylene copolymers (LCB-IPCs). Multifold H-type LCB structures were revealed with the LCB-IPCs, including two homologous structures based on polypropylene (PP- H -PP) and ethylene-propylene copolymer (EPC- H -EPC) individually, and a heterologous structure mixed of PP and ethylene-propylene copolymer (PP– H -EPC). Though all in minute amount, the LCB structures induced significant improvement in IPCs on many fronts. On melt properties, LCB-IPCs gained the unprecedented strain hardening property in extensional flow. On phase morphology, the LCB structures helped reduce the dispersion dimension of ethylene-propylene copolymer and the tendency of grain coarsening in post-preparation processing. On melt crystallization, the LCB structures enhanced the crystallization in an all-round way by prompting self-nucleation. On mechanical properties, by reinforcing the PP matrix and strengthening the interface to facilitate stress transfer between PP and EP copolymer, the LCB structures enabled an all-out promotion of mechanical properties with simultaneous reinforcement on stiffness and toughness. Fully implemented impact copolymerization of propylene preparing impact polypropylene copolymers was engaged with LCB agent 5-hexenylmethyldichlorosilane, which prompted formation of multifold H-shape LCB structures in the copolymers. The multifold LCB structures in turn induced profound improvement on multiple fronts of the copolymer properties. • ω -Alkenylmethyldichlorosilane is used as a LCB agent in impact copolymerization of propylene. • The new IPC polymers contain multifold H-type LCB structures. • The LCB structures induced significant improvement in properties of IPC on many fronts.

Improved melt strength and processability of impact copolymer polypropylene by introducing long‐chain branching via reactive extrusion with “ene” functionalized dendrimer

AbstractA generation two dendrimer (G2) having eight terminal double bonds has been prepared via esterification reaction from a dendritic precursor having eight hydroxyl end groups (G1). The reactive extrusion of impact co‐polymer polypropylene (ICP) with G1 resulted in improved processability while leading to enhanced melt strength in the case of linear low‐density polyethylene (LLDPE). G2 being an extension of G1, was melt grafted on ICP using a radical initiator to introduce long‐chain branching in the polymer backbone. The prepared samples were analyzed for their molecular weight distribution, thermal, rheological properties, and mechanical properties. Thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) analysis showed higher thermal stability and slightly higher crystallization temperature with grafting of G2 on ICP. The rheological analysis through melt flow index measurements and parallel plate rheometer indicated higher processability, melt strength, complex viscosity, and zero‐shear viscosity for ICP grafted with an optimized amount of G2. The presence of long‐chain branching was confirmed with an increase in activation energy for ICP modified with G2 as compared to neat ICP. Modified ICP samples retained their bulk mechanical properties as neat ICP.

Enhancing electrical properties of impact polypropylene copolymer for eco-friendly power cable insulation by manipulating the multiphase structure through molten-state annealing

Composite insulating materials with high electrical properties are integral for high voltage power cable. In this paper, we achieved significant increases by about 17% and 30% in breakdown strength and charge injecting transition field of impact polypropylene copolymer (IPC), a promising composite for power cable insulation, through 60 min molten-state annealing (MSA). To unravel the influencing mechanism of MSA on electrical properties, the multiphase structure evolution were investigated. Results showed that ethylene-propylene random copolymer (EPR) was separated from matrix with ongoing MSA. Meanwhile, two melting peaks were found in DSC curves. The one at lower temperature was raised from 142.2 °C to 144.6 °C after 60 min MSA, while the higher one remained unchanged, indicating the increase in thickness of partial lamellas, which was proved to be the reason for the increased deep trap level from 1.01 eV to 1.05 eV. Under 50 Hz AC electric field, electro-hole recombination was proposed to be the main origins of high-energy electrons, rather than acceleration under electric field. The greater the energy level of the deep trap, the smaller the energy released by recombination, resulting in reduced probability of collision ionization and thus increased breakdown strength. This work provides a new comprehending into the electrical breakdown and its enhancement of IPC eco-friendly power cable insulation.

Influence of temperature, residence time, and solvent/feedstock mass ratio on overall product distribution and oil products quality in ethanol liquefaction of 230 polypropylene impact copolymer

This work examined liquefaction of polypropylene into liquid products in the presence of ethanol with particular attention to the effect of temperature (325–400 °C), residence time (1–6 h) and solvent/feedstock mass ratio (1/1–4/1) on the overall product distribution, and composition of the oil products. The oil products obtained under the optimal reaction condition contained mainly alkanes, alkenes, alcohols and aromatics, which accounted for 42.41%, 22.81%, 3.51%, 1.05%, respectively. Increasing temperature and retention time enhanced aromatization reaction leading to increased yields of aromatic hydrocarbons. The higher heating value of the oil product was 45.72 MJ/Kg, which is comparable to the higher heating value (HHV) of gasoline. Volatility analysis shows that 50–85 wt% of the oil composition had similar boiling point range as gasoline (35−185 °C). These characterization results suggest that the oil could be used as a raw material for gasoline blendstock or chemicals. The interaction of three reaction parameters on the oil formation was further evaluated by the response surface method. Through the Box–Behnken design, the R2, F-value and p-value of analysis of variance were 0.9917, 93.20, and < 0.0001, respectively, showed that the model fitted well with actual experimental value. It is suggested that the reaction temperature affect the oil yield more significantly, compared to other two parameters. The response surface analysis showed that under the temperature of 376.7 °C, residence time 3.8 h and solvent/feedstock mass ratio of 1/1, oil yield of 98.32 wt% can be achieved without adding catalyst or hydrogen. This predication was also verified by experiment.

Time-domain NMR relaxometery – a green analytical tool for estimating physico-mechanical properties of polyolefins

Physical and mechanical properties of PE and PP are traditionally determined in the laboratory with methods as specified in ASTM/ISO standards. This is a time-consuming activity in any QC laboratory. In this paper, low-field (20 MHz) NMR has been used to quickly determine properties like density of HDPE, Xylene Solubles (XS) in homo-polymer PP & impact copolymer polypropylene (ICP), ethylene content (C2), flexural modulus (FM) and Izod impact strength of ICP, within a short span of time (∼1/4 h), allowing the plant to get expeditious feedback about the manufactured polymer grade enabling monitoring the manufacturing process more efficiently. The novelty in this work is that even calibration and predictive models for determining mechanical properties of polyolefins like FM and Izod impact strength have been successfully developed. Calibration models were built using known samples and validated using the validated sample set. For HDPE samples, a calibration model for determining the density could be prepared with R 2 of 0.867 and RMSEC of 0.0006 gcm−3. For homo PP samples, a predictive model for determining XS could be prepared with R 2 of 0.934 and RMSEC of 0.20 wt%. In case of calibration models for XS and C2 of ICP samples, R 2 = 0.924 each and RMSEC of 0.54 wt% & 0.45 wt%, respectively was obtained. A model for flexural modulus could be prepared with an R 2 and RMSEC of 0.935 & 28 MPa, respectively. Reasonable model could be developed for Izod impact strength (R 2 = 0.947 & 0.982 for low & high impact respectively). The properties of validation sample set were predicted based on the calibration models and good correlation was obtained between the lab data (QC data) and the predicted data.

Crystallization behavior of impact copolymer polypropylene revealed by fast scanning chip calorimetry analysis

The crystallization behaviors of two impact copolymer polypropylenes (ICP) were investigated by using fast scanning chip calorimetry (FSC) and micro-focus wide-angle X-ray diffraction (WAXD) techniques. Different crystallization peaks of these two samples during cooling were observed at cooling rates from 50 to 4000 K/s. For ICP-A, the crystallization of polypropylene (PP) matrix into α crystallites, polyethylene (PE) sequences in ethylene-propylene segmented copolymer (EsP), PP segments in ethylene-propylene block copolymer (EbP), and PP matrix into mesophase successively occurred from high to low temperatures. As the cooling rate increased, the crystallization of PP matrix into α crystallites, PP segments, and mesophase were suppressed one by one. Nevertheless, the crystallization of PE segments was hardly suppressed. For ICP-B, it showed almost the same crystallization behavior as ICP-A, except for the absence of independent crystallization peak of PP segments. The different crystallization performance in these two samples could be ascribed to their different chain microstructures.