Polypropylene Random Copolymer Research Articles

Multi walled carbon nanotubes induced viscoelastic response of polypropylene copolymer nanocomposites: Effect of filler loading on rheological percolation

Polypropylene random copolymer nanocomposites having 0.2–7.0 vol% multi-walled carbon nanotubes (MWCNTs) were prepared via melt processing. Transmission electron microscopy (TEM) was employed to determine the nano scale dispersion of carbon nanotubes. Linear viscoelastic behavior of these nanocomposites was investigated using parallel plate rheometry. Incorporation of carbon nanotubes in the polymer matrix resulted in higher complex viscosity (η*), storage (G′) and loss modulus (G″) as compared to neat polymer, especially in the low-frequency region, suggesting a change from liquid to solid-like behavior in the nanocomposites. By plotting storage modulus vs. carbon nanotube loading and fitting with a power law function, the rheological percolation threshold in these nanocomposites was observed at a loading of ∼0.27 vol% of MWCNTs. However, electrical percolation threshold was reported at ∼0.19 vol% of MWCNTs loading. The difference in the percolation thresholds is understood in terms of nanotube connectivity with nanotubes and polymer chain required for electrical conductivity and rheological percolation.

Effect of long chain branching on the rheological behavior, crystallization and mechanical properties of polypropylene random copolymer

Long chain branched polypropylene random copolymers (LCB-PPRs) were prepared via reactive extrusion with the addition of dicumyl peroxide (DCP) and various amounts of 1,6-hexanediol diacrylate (HDDA) into PPR. Fourier transform infrared spectrometer (FTIR) was applied to confirm the existence of branching and investigate the grafting degree for the modified PPRs. Melt flow index (MFI) and oscillatory shear rheological properties including complex viscosity, storage modulus, loss tangent and the Cole-Cole plots were studied to differentiate the LCB-PPRs from linear PPR. Differential scanning calorimetry (DSC) and polarized light microscopy (PLM) were used to study the melting and crystallization behavior and the spherulite morphology, respectively. Qualitative and quantitative analyses of rheological curves demonstrated the existence of LCB. The effect of the LCB on crystalline morphology, crystallization behavior and molecular mobility, and, thereby, the mechanical properties were studied and analyzed. Due to the entanglements between molecular chains and the nucleating effect of LCB, LCB-PPRs showed higher crystallization temperature and crystallinity, higher crystallization rate, more uniformly dispersed and much smaller crystallite compared with virgin PPR, thus giving rise to significantly improve impact strength. Moreover, the LCB-PPRs exhibited the improved yield strength. The mobility of the molecular chain segments, as demonstrated by dynamic mechanical analysis (DMA), was improved for the modified PPRs, which also contributed to the improvement of their mechanical properties.

Toughened polypropylene random copolymer with olefin block copolymer

In this work, the toughening effect of olefin block copolymer (OBC) on polypropylene random copolymer (PPR) at room and low temperature (0°C) was investigated. Mechanical tests showed that OBC is an effective impact modifier for PPR. By addition of only 5wt% of OBC, the notched Izod impact strength of resulting blends at room temperature and 0°C are 66.5, 9.27kJ/m2, which are increased 135.8 and 43.9%, respectively. This value for blends containing 10wt% OBC at 0°C is 60.2kJ/m2, which is approximately eight times higher than that of pristine PPR at same temperature. Due to the high melting point of OBC, the decline of rigidity caused by its addition is rather slight. The tensile strength and flexural modulus for blends containing 10wt% OBC is only 8.3 and 11.3% lower than that of pristine PPR. The investigation of morphology, crystallization and rheological behaviors suggested that the great improvement of toughness might be attributed to the decrease of PPR spherulites size and the excellent compatibility between PPR matrix and OBC dispersed phase. This work offers a simple and effective approach to produce PPR with stiffness–toughness balance.

Migration of Stabilizers from Polypropylene into Simulated Food

ABSTRACTThis study has investigated the migration of stabilizers from three polypropylene materials: a polypropylene homopolymer, a polypropylene block copolymer, and a polypropylene random copolymer in 10% ethanol, 3% acetic acid, 20% ethanol, 50% ethanol, and isooctane according to Regulation (EU) No. 10/2011. Measurements were performed at 20, 40, and 70°C and migration was evaluated from 10 min to 10 days. Measurements were performed by high-performance liquid chromatography (HPLC) with external calibration. The HPLC method provided high correlation coefficients, good precision, good accuracy, and suitable reproducibility. Diffusion coefficients for stabilizers were obtained using a rigorous model based on Fick’s second law and the values were between 6.1 × 10−13 and 3.8 × 10−9 cm2 s−1. By applying an Arrhenius-type equation to the diffusion coefficients, an estimation of activation energy of the diffusion was obtained. The activation energies were from 39.97 to 98.75 kJ mol−1 for the stabilizers. The results indicate that the polypropylene material structure influenced the migration rate, which decreased in the order of the increasing crystallinity in the materials. The diffusion coefficients for stabilizers in the polypropylene random copolymer were higher than in the polypropylene block copolymer and polypropylene homopolymer. The random polypropylene copolymer had the lowest activation energy. These results show that a higher diffusion coefficient indicates a higher migration rate, and a system with a lower activation energy allows more migration.

Synergistic effect of self-assembling nucleating agent and crystallization promoter on polypropylene random copolymer pipes via rotation extrusion

In this study, high hoop tensile strength and toughness polypropylene random copolymer (PPR) pipes were successfully prepared through rotation extrusion and synergistic effect of self-assembling nucleating agent (TMB-5) and crystallization promoter (isotactic polypropylene, iPP). The result indicated low temperature toughness of PPR pipes could be improved by incorporating TMB-5 and iPP, as the result of highly improved PPR crystallization capability and abundant β-form crystal production. Both molecular chains and anisotropic crystallites deviated off the axial direction due to the hoop stress generated by rotation extrusion, leading to increased hoop orientation and pronouncing enhancement in hoop strength. Accordingly, the hoop tensile strength and impact strength of the modified PPR pipe reached 28.9MPa and 5.7kJ/m2, increased by 126% and 43% compared to the convention-extruded PPR pipe. POLYM. ENG. SCI., 56:866–873, 2016. © 2016 Society of Plastics Engineers

Self-reinforced composites based on commercial PP woven fabrics and a random PP copolymer modified with quartz

Self-reinforced composites based on commercial polypropylene (PP) woven fabrics and a random PP copolymer modified with quartz were obtained by film stacking. The effect of the incorporation of quartz on the materials fracture and failure behavior was studied through uniaxial tensile tests and quasi-static fracture experiments. Acoustic emission analysis was also performed in situ in the tensile tests. A higher consolidation quality was obtained for the composites containing quartz. In the composite with random PP modified with 5 wt% quartz, the higher consolidation and the better dispersion of quartz particles positively impacted on the materials tensile and fracture behavior. From the results of acoustic emission analysis, fiber fracture appears as the dominant failure mechanism in the investigated composites. Copyright © 2016 John Wiley & Sons, Ltd.

Influence of morphology evolution on the mechanical properties of beta nucleated isotactic polypropylene in presence of polypropylene random copolymer

A promising method was developed by adding polypropylene random copolymer (co-PP) and β-nucleating agent (β-NA) simultaneously into isotactic polypropylene (iPP) matrix to improve its toughness. Results showed that the co-PP chains promoted crystal refinement, and the rubbery phases corresponding to the propylene–ethylene random segments offered superior toughness. This proves that crystal morphology, which correlates with β-NA content, is another important factor that determines toughness and tensile strength in addition to β crystal content. Furthermore, a mechanism for the morphology evolution is proposed. This study shows the feasibility of improving the mechanical properties of iPP and expanding its applications.

A novel online rheometer for elongational viscosity measurement of polymer melts

This paper focuses on the measurement of elongational viscosity of polymer melts and filled compounds using a novel online rheometer. We developed a device with two slit sections and a hyperbolic contraction part in between, which allows for constant monitoring of both shear and elongational viscosity during an extrusion process. Due to the favorable design of the hyperbolic contraction, pressure transducers can be incorporated directly into the flow channels, which prevents material accumulation in pressure holes. The results of a pipe-grade polypropylene random copolymer melt are in good accordance with Sentmanat Extensional Rheometer (SER) measurements, in contrast to other methods such as Cogswell analysis of High Pressure Capillary Rheometer (HPCR) data or measurement on a wedge-shaped slit die, which fail to predict the true non-Newtonian behavior of the melt. In addition, we present the results of a polypropylene homopolymer intended for thermoformed packaging applications, a glass fiber and a talc compound, which could all be successfully characterized using our rheometer.

Enhanced mechanics in injection molded isotactic polypropylene/polypropylene random copolymer blends via introducing network-like crystal structure

The crystallization behavior, rheological behavior, mechanical properties and microstructures of injection molded isotactic polypropylene (iPP), polypropylene random copolymer (co-PP) and iPP/co-PP blends were investigated. Differential scanning calorimetry (DSC) and dynamic rheological analysis illustrated that iPP and co-PP were compatible in the blends and co-PP uniformly dispersed in the iPP phase. Polarizing optical microscope (POM) was adopted to observe the crystal size and morphology evolution. The results of mechanical properties and scanning electron microscopy (SEM) indicated that the crystal size of iPP in iPP/co-PP blends (10 wt% co-PP + 90 wt% iPP and 30 wt% co-PP + 70 wt% iPP) radically decreased after the incorporation of co-PP. During crystallization, the molecular chain segments of co-PP could penetrate iPP spherulites and form a network-like crystalline structure. The network-like crystal structure could effectively transmit stress and consume more energy to overcome intermolecular forces to resist stretching. In this way, the strength would improve to a certain degree. The impact fracture mechanism of iPP/co-PP blends is quasi ductile fracture by multiple crazes. Our work discovered that the blends containing 10 wt% and 30 wt% of co-PP exhibited prominent toughness and reinforcement.

Dynamic mechanical properties, crystallization behaviors, and low‐temperature performance of polypropylene random copolymer composites

ABSTRACTIn this study, polypropylene random copolymer (PPR) composites were prepared by the addition of either three kinds of thermoplastic rubber (TPR) modifiers (types 2088A, 2095, and 2096) or an ethylene–octene copolymer (POE)/high‐density polyethylene (HDPE; 2 :1 w/w) blend. Differential scanning calorimetry, wide‐angle X‐ray diffraction, and dynamic mechanical analysis were used to characterize the crystallization behaviors and dynamic mechanical properties of the PPR composites. The results indicated that PPR/POE/HDPE and PPR/TPR2088A had better comprehensive mechanical properties, especially the low‐temperature toughness among all of the samples. The obtained PPR/POE/HDPE blends showed a high toughness and good stiffness in the temperature interval from −10 to 23°C with the addition of only 10 wt % POE/HDPE. When the temperature continued to fall below −10°C, the PPR/TPR2088A composites exhibited a better impact toughness without a loss of too much stiffness. The good low‐temperature toughness of those two composites was attributed to both the decrease in the crystallinity and the uniform dispersion, obvious interfacial adhesion, and cavitation ability of POE/HDPE and TPR2088A in the PPR matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42960.

Designing of carbon nanotube/polymer composites using melt recirculation approach: Effect of aspect ratio on mechanical, electrical and EMI shielding response

ABSTRACT The paper describes the effect of aspect ratio of multiwall carbon nanotubes (MCNTs) on the electrical, mechanical and electromagnetic properties of polypropylene random copolymer (PPC). Long and short MCNTs with aspect ratio of ~ 1356–1937 and ~ 158 respectively were melt-blended with PPC in a micro twin screw extruder with melt recirculation that allow the formation of composites having ~ 15 wt.% MCNTs. The good dispersion was confirmed by scanning electron microscopy and observation of electrical conductivity at low percolation threshold (0.45 and 1.07 wt.% for l- & s-MCNT/PPC composite respectively) and improvement of modulus and strength. The 15 wt.% l-MCNTs and s-MCNT loaded composites show 52% and 60% improvement in modulus respectively and 20% & 18% improvement in strength over neat PPC. The electromagnetic interference (EMI) shielding response (in 8.2–12.4 GHz frequency range) revealed that l-MCNT based PPC composites display better shielding at lower loading (up to 4 wt.%) while s-MCNT show better attenuation at higher loadings. The realization shielding effectiveness value of − 27 dB (> 99% attenuation) respectively for l-MCNT composites: and − 37 dB (> 99.9% attenuation) for s-MCNTs composites at 15 wt.% reflect their potential for making light weight and structurally strong EMI shields.

Injection Blow Moulding Single Stage Process – Approach of the Material Behaviour in Process Conditions and Numerical Simulation

Single stage injection blow moulding process, without preform storage and reheat, could be run on a standard injection moulding machine, with the aim of producing short series of specific hollow parts. In this process, the preform is being blow moulded after a short cooling time. Polypropylene (Random copolymer) is a suitable material for this type of process. The preform has to remain sufficiently melted to be blown. This single stage process introduces temperature gradients, molecular orientation, high stretch rates and high cooling rates. These constraints lead to a small processing window, and in practice, the process takes place between the melting temperature and the crystallization temperature. To investigates the mechanical behaviour in conditions as close to the process as possible, we ran a series of experiments: First, Dynamical Mechanical Analysis was performed starting from the solid state at room temperature and ending in the vicinity of the melting temperature. Conversely, oscillatory rheometry was also performed starting this time from the molten state at 200°C and decreasing the temperature down to the vicinity of the crystallization temperature. The influence of the shear rate and of the cooling kinetics on the enhancement of the mechanical properties when starting from the melt is discussed. This enhancement is attributed to the crystallization of the material. The question of the crystallization occurring at such high stretch rates and high cooling rates is open. A viscous Cross model has been proved to be relevant to the problem. Thermal dependence is assumed by an Arrhenius law. The process is simulated through a finite element code (POLYFLOW software) in the Ansys Workbench framework. Thickness measurements using image analysis are performed and comparison with the simulation results is satisfactory.

Joint effects of rotational extrusion and TiO2 on performance and antimicrobial properties of extruded polypropylene copolymer pipes

ABSTRACTIn this study, effects of titanium dioxide (TiO2) and rotation extrusion on structures and properties of polypropylene random copolymer (PPR) pipes were investigated. The experimental results showed that with the presence of TiO2, not only the antibacterial ability of PPR pipe was improved significantly but also the toughness was enhanced since a large number of PP chains were promoted to crystallize into β‐form crystals. Furthermore, when rotation extrusion was introduced into the process of PPR pipe, the drag hoop flow caused by mandrel and die rotation was superposed on the axial flow, so the polymer melts in the annulus underwent a helical flow and its flow direction deviated from the axis to drive the molecular orientation off the axial direction, bringing out the increased hoop strength. As a result, PPR pipe with excellent performance was prepared under the combined effect of rotation extrusion and TiO2. The antibacterial activity was 99.2%, the hoop tensile strength reached 27.5 MPa, 67.7% higher than that of the convention‐extruded PPR pipe with TiO2, and the impact strength was 10.9 kJ/m2, increased by 81.6% compared to that of the rotation‐extruded pure PPR pipe. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42410.

Enhanced ultraviolet resistance of polypropylene random copolymer filled by ZnO-supported mesoporous zeolite

To enhance the ultraviolet resistance of ZnO based polymer materials, ZnO-supported mesoporous zeolite (M-ZnO) was prepared and characterized by atomic absorption spectroscopy and scanning electron microscopy. The ultraviolet resistance, crystallization behavior and melting characteristics of ZnO and M-ZnO filled PPR composites were compared by FTIR spectra and differential scanning calorimetry. The ultraviolet resistance of M-ZnO filled PPR composites is higher than that of ZnO filled PPR composites, indicating higher ultraviolet resistance of M-ZnO than that of ZnO. The crystallization temperatures of mesoporous zeolite filled PPR were higher than those of M-ZnO and decreased with increasing UV-irradiation time. But the crystallization temperatures of M-ZnO filled PPR composites were not influenced by UV-irradiation time. The ZnO supported on the surface of zeolite is effective in enhancing the ultraviolet resistance of ZnO based polymer materials.

Excellent electromagnetic interference shielding and mechanical properties of high loading carbon-nanotubes/polymer composites designed using melt recirculation equipped twin-screw extruder

This paper describes for the first time a facile, scalable and commercially viable melt blending approach involving use of twin-screw extruder with melt recirculation provision, for uniform dispersion of up to 4.6vol% multiwall carbon nanotubes (MWCNTs) within polypropylene random copolymer (PPCP). Morphological characterization of PPCP/MWCNT nanoscale composites (NCs) was done using scanning electron microscopy and transmission electron microscopy, which show good dispersion of MWCNTs in the PPCP matrix even at high loadings and confirm the formation of true NCs. The improved dispersion leads to the formation of electrically conducting three dimensional networks of MWCNTs within PPCP matrix at very low percolation threshold (∼0.19vol%). The attainment of dc conductivity value of ∼10−3S/cm, tensile strength of ∼42MPa and good thermal stability for 4.6vol% MWCNTs loading NC along with electromagnetic interference (EMI) shielding effectiveness (SE) value of −47dB (>99.99% attenuation), demonstrate its potential for making light weight, mechanically strong and thermally stable EMI shields. These NCs also display specific SE value of ∼−51dBcm3/g which is highest among unfoamed polymer NCs.

Development of Films of Novel Polypropylene based Nanomaterials for Food Packaging Application

In order to design new antimicrobial nanocomposites with properties for food packaging application, films of polypropylene random copolymer (PPR), PPR/Poly-β-pinene (PβP), PPR/clay and PPR/PβP/clay were prepared by melt extrusion. Structural, morphological, mechanical, barrier, antimicrobial properties and thermal stability of the films were determined. PPR and PβP always form a homogeneous system in the amorphous phase; in the binary PPR/clay system, PPR molecules intercalate the clay galleries; in the ternary PPR/PβP/clay system, the miscibility between PPR and PβP prevents the intercalation of the PPR macromolecules into the clay galleries. The addition of clay and PβP increased the thermal stability and the tensile mechanical properties of PPR and reduced the oxygen transmission rate and the water vapor transmission rate compared with plain PPR. Films of nanomaterials containing PβP provided a reduction of the test microorganisms (Escherichia coli 25922) of 24% comparing to the control (PPR/clay film). Copyright © 2015 John Wiley & Sons, Ltd.

Influence of melt structure on the crystallization behavior and polymorphic composition of polypropylene random copolymer

Polypropylene random copolymer (PPR) is one of important polypropylene types for the application fields. However, due to the random copolymer chain configuration, it is difficult to obtain high proportion of β-phase even under the influence of β-nucleating agent (β-NA). In this study, the melt structure (namely, the content of ordered structures in the melt) of β-nucleated ethylene-copolymerized PPR (β-PPR) was controlled by tuning the fusion temperature (Tf), and its impact on the crystallization and polymorphic behavior of β-PPR was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), polarized optical microscopy (PLM) and scanning electronic microscopy (SEM). The result revealed that compared with the β-nucleated iPP homo-polymer, it is more difficult for β-PPR to form β-crystals; interestingly, when Tf is in the temperature range of 162–173°C, the ordered structures survived in melt exhibit high β-nucleation efficiency under the influence of β-NA, resulting in significant increase of β-phase proportion and evident variation of crystalline morphology, which is called the Ordered Structure Effect (OSE). Moreover, through investigating the self-nucleation behavior and equilibrium melting temperature of pure PPR (non-nucleated PPR), the physical nature of the lower and upper limiting Tf temperatures for the occurrence of OSE in β-PPR was explored; the role of ethylene co-monomer in the occurrence of OSE was discussed.

Preparation and Properties of Core-Shell Particles Filled β-Nucleated Polypropylene Random Copolymer Composites

To provide polypropylene random copolymer (PPR) with excellent toughness without lowering its rigidity, a novel kind of core-shell particles (CSP) and β nucleating agent (β-NA) were incorporated into PPR by melt blending. The CSP, in which nano-CaCO3 acted as the core and polyethylene (PE) formed the shell, was also prepared through melt blending. The effects of different proportion of PE shell and nano-CaCO3 core on the properties of β-modified PPR composites were investigated. The dispersion and morphology of CSP were studied by transmission electron microscopy (TEM) and the results showed that the CSP dispersed fairly well in the PPR matrix and the core-shell structure was successfully formed. The nano-CaCO3 core was completely encapsulated by PE, especially at the 50/50 weight ratio. The crystallization behaviour of the PPR composites was characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). All the results showed that the relative content of β-form crystal was greatly enhanced with the incorporation of β-NA. Furthermore, the weight ratio change of PE/nano-CaCO3 could also increase the relative content of the β-form crystal. Under the combined effects of β-modification and CSP, the mechanical properties of the PPR composites were greatly enhanced without reducing its rigidity.

Failure of compression molded all-polyolefin composites studied by acoustic emission

This paper is aimed at studying the failure behavior of polyolefin-based self-reinforced polymer composites (SRPCs) via acoustic emission (AE). Three matrix materials (ethylene octene copolymer (EOC), polypropylene-based ther- moplastic elastomer (ePP), random polypropylene copolymer (rPP), and three kinds of reinforcing structures of PP homopolymer (unidirectional (UD), cross-ply (CP) and woven fabric (WF)) were used. SRPCs were produced by compres- sion molding using the film-stacking method. The composites were characterized by mechanical tests combined with in situ assessment of the burst-type AE events. The results showed that rPP matrix and UD reinforcement produced the greatest reinforcement, with a tensile strength more than six times as high as that of the matrix and a Young's modulus nearly dou- bled compared to the neat matrix. The number of the detected AE events increased with increasing Young's modulus of the applied matrices being associated with reduced sound damping. The AE amplitude distributions shows that failure of the SRPC structure produces AE signals in a broad amplitude range, but the highest detected amplitude range can be clearly linked to fiber fractures.

Effect of annealing temperature on low-temperature toughness of β-nucleated polypropylene random copolymer/ethylene-propylene-diene terpolymer blends

In this study, the effect of annealing temperature on the impact toughness of β-nucleated polypropylene random copolymer (PPR) and ethylene-propylene-diene terpolymer (EPDM) blends was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). Interestingly, the impact strength of β-PPR/20EPDM blend annealed at 120 °C is 1.8 times as high as that of unannealed samples. In addition, the crystalline structure, the relaxation of chain segments and fracture morphology of β-PPR/EPDM blends were also investigated to explore the toughening mechanism related to annealing. The results show that annealing at moderate temperatures results in the improvement of integrity of the crystal structure and the relative content of β-phase. The work provides a possible method to toughen the semicrystalline polymer at low temperatures by annealing.