Pure iPP Research Articles

Shear‐Induced Skin‐Core Structure of Molten Isotactic Polypropylene and the Formation of β‐Crystal

AbstractThe study of crystallization behavior and crystalline morphology of polymer melt under shear flow is of great interest due to the strong effect of flow field on the final properties of polymer products in the practical processing. In this respect, the shearing hot stage provides a unique tool which monitors sensitively the changes in crystalline structure induced by precise experimental conditions. Herein, the impacts of both melting temperature and shear rate on the crystallization behavior of isotactic polypropylene (iPP) melt are investigated. Under static conditions, there are only random spherulite structures. Once shear is involved, the cylindrite‐layers appear near both surfaces of the sample, which is consistent with the skin‐core structure in the injection molded parts. Meanwhile, the β‐crystals can be developed and are related to the molecular orientation, depending on the applied melting temperatures and shear rates. More interestingly, the crystallinity of β‐crystal in the pure iPP can reach 15%. The above results indicate that the melting temperature and shear rate are important factors in determining the β‐form crystal development of iPP matrix.

Nonisothermal Crystallization, Melting Behaviors, and Mechanical Properties of Isotactic Polypropylene Nucleated with a Liquid Crystalline Polymer

The nonisothermal crystallization and melting behaviors of isotactic polypropylene (iPP) nucleated by a main-chain liquid crystalline polyester (poly(4,4′-bis(6-hydroxyhexyloxy)biphenyl phenylsuccinate), PBDPS) as a β-nucleating agent have been investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarizing optical microscopy (POM). The effect of PBDPS on the mechanical properties of iPP was also studied. The results showed that nonisothermal crystallization kinetics of pure iPP and iPP/PBDPS blends can be described by the Jeziorny and Mo methods. PBDPS can induce both α and β crystals for iPP, with β-nucleation playing the more prominent role. The relative content of the β-crystal (kβ) increased as the PBDPS content increased and the cooling rate decreased. The kβ value reached 75%, even with a fast cooling rate of 40 °C/min. The elongation at break, flexural modulus, impact strength, and heat deformation temperature (HDT) are improved by introducing PBDPS, wh...

Competition effect of shear‐induced nuclei and multiwalled carbon nanotubes (MWCNT) on β‐isotactic polypropylene (iPP) formation in preshear injection‐molded iPP/MWCNT nanocomposites

In this study, the influence of multiwalled carbon nanotubes (MWCNT) on β‐isotactic polypropylene (iPP) formation in preshear injection‐molded iPP/MWCNT nanocomposites is investigated layer by layer by wide angle X‐ray diffraction (WAXD). WAXD results suggest that in preshear injection‐molded pure iPP, β‐iPP exists in not only the shear region, but also the core region as a result of preshear‐induced nucleation. The addition of MWCNT can inhibit the β‐iPP formation. As the depth away from the specimen surface is decreased, the inhibiting effect is decreased. The reason responsible for that is given as follows: (1) with the addition of MWCNT, extra nuclei are induced during preshear. Both MWCNT and extra nuclei serve as α‐iPP nucleation point. Therefore, the formation of β‐iPP is restricted; (2) the cooling rate gradient is widely accepted to exist in the injection molded sample. A larger cooling rate at a smaller depth will give rise to a lower α‐iPP crystallization onset temperature and a lower nucleation efficiency of MWCNT. Since that β‐iPP grows only in the temperature range of 105°C‐140°C, the inhibiting effect of MWCNT on β‐iPP becomes weaker as the depth is decreased. POLYM. COMPOS., 39:E1149–E1158, 2018. © 2017 Society of Plastics Engineers

Crystallization kinetics of ethylene-co-propylene rubber/isotactic polypropylene blend investigated via chip-calorimeter measurement

Differential scanning calorimetry measurement via fast-scan chip-calorimeter Flash DSC1 has been widely applied to investigate the crystallization kinetics of homopolymer and random copolymers. We expanded the measurement to the crystallization kinetics of isotactic polypropylene (iPP) blending with 29.3wt% ethylene-co-propylene rubber (EPR) that contains 39.5wt% ethylene monomers (toughening iPP). The temperature dependence of half-crystallization times of the blend show three regions of deviations from the parallel results of pure iPP, reflecting the effect of interplay between phase separation and crystallization. We attributed faster crystallization in the high-temperature region to crystal nucleation accelerated by the interfaces of two incompatible components, attributed slower crystallization in the middle-temperature region to crystal nucleation retarded by the crystallization of ethylene sequences in the minor EPR component, and attributed faster crystallization in the low-temperature region to crystal nucleation accelerated by the crystallization of propylene sequences in the minor EPR component. The suppression of crystallization on fast cooling as well as the variation of Avrami indexes support the scenario of crystallization competition in the middle temperature region.

Block Copolymer Micelle Toughened Isotactic Polypropylene

A series of compositionally symmetric poly(ethylene-alt-propylene)-b-poly(ethylene-ran-ethyl ethylene) (PEP–PEEE) diblock copolymers were synthesized by anionic polymerization of isoprene and butadiene followed by heterogeneous catalytic hydrogenation. These materials were melt blended with isotactic polypropylene (iPP) at concentrations between 1.25 and 20 wt %, and the resulting morphologies were investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Uniformly dispersed micelles with an average diameter of approximately 100 nm were obtained in blends with PEP-PEEE molecular weights of 100 and 240 kg/mol. Tensile tests showed a 25-fold increase in the strain at break at a concentration of just 2.5 wt % with no discernible loss in elastic modulus or tensile strength. Blends containing 5 and 10 wt % micelles displayed 5 and 12 times the Izod impact strength of the pure iPP, respectively. Conversely, blends prepared with PEP homopolymer formed larger particles (≈0....

The “Nodular” α Form of Isotactic Polypropylene: Stiff and Strong Polypropylene with High Deformability

A study of the nucleating effects of isotactic poly(trimethylallylsilane) (iPTMAS) and poly(vinylcyclohexane) (iPVCH) for isotactic polypropylene (iPP) and their influence on the mechanical behavior of iPP is reported. The particles of catalyst are covered by poly(trimethylallylsilane) or poly(vinylcyclohexane) by polymerization of the corresponding monomers before polymerization of propylene. The method guarantees that the nucleating agents are perfectly dispersed into the iPP samples, with their consequent high efficiency. Isotactic poly(vinylcyclohexane) and poly(trimethylallylsilane) favor crystallization from the melt of α and β forms, respectively. Both nucleating agents affect the morphology greatly reducing the size of shperulites. This in turn affects the mechanical properties improving ductility and flexibility. All nucleated samples crystallize by rapid cooling from the melt in the α form and not in the mesophase, as occurs in the pure iPP. The resulting α form presents nodular crystals and beh...

무수 말레익산이 그래프트된 폴리프로필렌을 상용화제로 사용한 아이소탁틱 폴리프로필렌/세균성 셀룰로오스 복합체의 기계적/유변학적 물성

To improve the mechanical performance of isotactic polypropylene (iPP), the iPP/bacterial cellulose (BC) composites were prepared. The tensile and impact strength of the composites were maximized (38.21MPa and 2.812 KJ/m²) when maleic anhydride grafted polypropylene (MAPP) content was 7 wt%, the tensile modulus was increased with the higher MAPP content and the maximum value was 1858.39 MPa. Compared with pure iPP, the tensile strength, impact strength and tensile modulus increased by 6.32 MPa, 0.75 KJ/m², and 279.68 MPa, respectively. Compared with the control group (the sample which added BC but no MAPP added), the tensile strength, impact strength and tensile modulus increased by 5.61 MPa, 0.692 KJ/m², and 11.24 MPa, respectively. Moreover, the elongation at break of the composites was decreased. Besides, the rheological results and SEM photographs indicated that with the addition of MAPP, the compatibility of the composites was improved greatly, which demonstrated the increase of the mechanical properties of the composites.

Effects of poly(propylene carbonate) additive prepared from carbon dioxide on the tensile properties of polypropylene

ABSTRACTWe investigated the effect of a rubbery poly(propylene carbonate) (PPC) additive on the tensile properties of isotactic polypropylene (iPP). PPC materials were produced from carbon dioxide gas. Although the elongation of iPP was reduced at higher elongation speeds, PPC addition improved the elongation at break at higher elongation speeds. iPP/PPC blends showed a high drawability while maintaining a high stress level. The failure mechanisms at high elongation speeds were different between the iPP and iPP/PPC samples. Craze‐like voids appeared along the stretching direction for pure iPP, whereas the PPC additive yielded craze‐like voids that were perpendicular to the stretching direction. The addition of PPC doped with carbon nanodots enhanced the yield toughness of iPP at high elongation speeds. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45266.

Optimization of tensile properties of injection molded α-nucleated polypropylene using response surface methodology

Tensile properties are among the significant properties of isotactic polypropylene (iPP). The mechanical properties including the tensile properties are fairly dependent on the overall crystallinity and crystallite size and their distribution in molded product, type of crystal structure and testing conditions. In presence of α-nucleating agents, the crystallization rate and onset temperature of isotactic PP increase. In this paper, the role of externally added commercial α-nucleating agent HPN-20E (Milliken Inc.) on tensile properties was investigated with respect to tensile properties of pure iPP. The experimental part includes the use of design of experiment (DoE) - response surface methodology (RSM) with central composite design (CCD) having three factors namely mold temperature, melt temperature and injection rate. Two levels of each factor with six centre points and five numbers of replicates were selected. The nucleating agent, HPN-20E, was added 1.0% by wt. in iPP (mfr 11.0 g/10min) using a lab scale co-rotating twin screw extruder. The compounded pellets were dried at 85 °C in a circulating hot air oven for 24 h. The tensile samples (ASTM-638D, type-I) were molded on a micro-injection molding machine (make BabyPlast, Italy). The samples were tested for tensile properties on a universal testing machine (make Lloyds, USA). The measured responses were tensile strength (MPa), Young's modulus (MPa) and work to break (N.mm). The same experimental procedure was also followed for pure iPP and same responses were measured to set the baseline of experiment. The analysis of variance (ANOVA) tests unearth that mold and melt temperatures are highly interacting in nature. That is why previous attempts based on traditional way of varying one parameter at a time were not so successful to relate tensile properties with injection molding variables. The RSM tests resulted into useful quantitative relationship between the tensile properties and injection molding process variables.

Uniform fiber orientation and transcrystallization formed in isotactic polypropylene/short glass fiber composites via a shear‐induced orientation extrusion

The orientation of short glass fibers (SGFs) and the interfacial interaction between SGFs and isotactic polypropylene (iPP) matrix play main roles in the final properties of the iPP/SGFs composites. Here we show a self‐design shear‐induced orientation extrusion (SIOE) to efficiently fabricate the iPP/SGFs composites with evenly dispersion and orientation of SGFs in the whole iPP matrix. The shear stress and the orientation of SGFs are also benefit to induce transcrystals which enhance the interfacial interaction between SGFs and iPP matrix. The crystallinity in average of the iPP/5.0 wt% SGFs composites shows nearly 10% higher than that of pure iPP extruded by the SIOE system. The iPP/5.0 wt% SGFs composites extruded by high shear stress not only exhibit higher yield strength and Young's modulus than that of the composites extruded by low shear stress but also maintain high tensile strength and strain at break. The enhancement of mechanical properties is ascribed to the uniform dispersion and orientation of SGFs, high crystallinity, and high interfacial interaction between SGFs and iPP matrix induced by transcrystals. POLYM. COMPOS., 39:3168–3177, 2018. © 2017 Society of Plastics Engineers

Polypropylene films with high barrier performance via crystal morphology manipulation

In this work, a simple and cost-effective method is proposed to prepare iPP films with high barrier properties. By adding a very small amount of β-nucleating agent, three types of β-crystal morphologies, namely, β-spherulites, β-transcrystals and β-“flower”-like agglomerates are sequentially obtained in iPP with the increasing processing temperature. Among β-nucleated iPP films, the one with β-“flower”-like agglomerates demonstrates the best water vapor and oxygen barrier performances, whose water permeability coefficient is decreased by 50.3% and oxygen permeability coefficient by 67.5%, compared to pure iPP films. Refined crystals, sufficient connection within the crystallites and lamellae parallel to the gas flow direction in iPP with β-“flower”-like agglomerates may force the gas molecules to take longer and more tortuous pathway, thus resulting in excellent barrier properties. Our work provides a new idea to prepare iPP films with high barrier properties by simply manipulating their crystal morphology.

Constructing a special ‘sosatie’ structure to finely dispersing MWCNT for enhanced electrical conductivity, ultra-high dielectric performance and toughness of iPP/OBC/MWCNT nanocomposites

An isotactic polypropylene (iPP) nanocomposite with low percolation threshold, ultrahigh dielectric permittivity and toughness by controlling the dispersion of multi-walled carbon nanotubes (MWCNTs) through ethylene-α-octene block copolymer (OBC), is reported. A special ‘sosatie’ structure, i.e. finely dispersed long MWCNTs inserted in OBC phase uniformly distributed in the continuous iPP matrix, was constructed through simple melt compounding process. The percolation threshold of the prepared iPP/OBC/MWCNT nanocomposites was ca. 0.5 vol%, lower than that of iPP/MWCNT nanocomposites. The iPP/OBC/MWCNT nanocomposites exhibited an ultrahigh dielectric permittivity (ca. 9000) at 100 Hz and a very low dielectric loss (ca. 1.5). MWCNTs also improved the compatibility between iPP and OBC components, leading to a high impact strength of iPP/OBC/MWCNT nanocomposites (about 13 times higher than pure iPP when the content of MWCNT was 1.49 vol%). Thus, the approach reported in this work can provide a new and convenient route to prepare high-performance polymer nanocomposite dielectric materials with low percolation thresholds and balanced mechanical properties.

Structures and properties of low‐shrinkage polypropylene composites

ABSTRACTThe high shrinkage and the low impact strength severely limit the applications of the isotactic polypropylene (iPP). In this article, we studied the shrinkage, microstructure, and mechanical properties of the composites consisted of iPP, short glass fiber (GF), maleic anhydride grafted polypropylene (MPP), maleic anhydride grafted polypropylene/polyolefin elastomer (MPPPOE) or composite toughening agents (CTAs). The results show that the shrinkage of the composite with 40% GF reduces to 0.0754% (24 h) and 0.0893(48 h), respectively, under room temperature, which is far lower than the shrinkage [1.782% (24 h) and 1.821% (48 h)] of the pure iPP. For the composite of PP/GF/MPPPOE/CTAs (55/30/5/10), the tensile strength increases to 65.53 MPa (33.8 MPa for pure iPP), the tensile modulus is 1445 MPa which is 136% higher than pure iPP, and the izod impact strength reaches 22.72 kJ/m2 (only 5.28 kJ/m2 for pure iPP). Not only the scale stability of iPP is remarkably improved, but also the comprehensive mechanical properties are enhanced drastically. This work may generate potential opportunities for iPP in those applications demanding high scale stability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44275.

Alkylated and restored graphene oxide nanoribbon-reinforced isotactic-polypropylene nanocomposites

Nanostructured carbon materials have outstanding physical properties and high aspect ratios. They have attracted much attention for use as polymer composite reinforcements. In this study, alkylated and reduced graphene oxide nanoribbons (A-rGONRs) were prepared by unzipping multi-walled carbon nanotubes (MWCNTs), followed by a simple alkylation/chemical reduction process using a Dean-Stark trap. A-rGONRs have morphologies with width 30–50 nm and lengths of several micrometers (aspect ratio >100). They are similar to one-dimensional MWCNTs, but with extended interfacial areas and edge functional sites. Approximately 25 wt% of the alkyl chains were chemically introduced onto the surface of A-rGONRs, which gave rise to hydrophobic properties and a surface energy of 23.8 mJ m−2. A stable A-rGONRs suspension was achieved in xylene even after 24 h. Through a wet process, A-rGONRs were homogeneously dispersed in an isotactic polypropylene (iPP) host. iPP/A-rGONRs nanocomposites showed significant enhancements in thermal and mechanical properties when compared to pure iPP.

Simultaneously improving the tensile and impact properties of isotactic polypropylene with the cooperation of co-PP and β-nucleating agent through pressure vibration injection molding

In this article, crystalline morphology and molecular orientation of isotactic polypropylene (iPP), random copolymerized polypropylene (co-PP) and β-nucleating agent (β-NA) composites prepared by pressure vibration injection molding (PVIM) have been investigated via polarized light microscopy, scanning electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Results demonstrated that the interaction between co-PP and iPP molecular chains was beneficial for the mechanical improvement and the introduction of β-NA further improved the toughness of iPP. In addition, after applying the pressure vibration injection molding (PVIM) technology, the shear layer thickness increased remarkably and the tensile strength improved consequently. Thus, the strength and toughness of iPP/co-PP/β-NA composites prepared by PVIM were simultaneously improved compared to those of the pure iPP prepared by conventional injection molding (CIM): the impact toughness was increased by five times and tensile strength was increased by 9 MPa. This work provided a new method to further enhance the properties of iPP/co-PP composites through dynamic processing strategy.

Nonisothermal crystallization kinetics in isotactic polypropylene/microcrystalline cellulose (II) composites

This study investigates the polymorphous transformation of microcrystalline cellulose at different NaOH concentrations and the nonisothermal crystallization kinetics of polypropylene/microcrystalline cellulose (II) composites by differential scanning calorimetric technique (DSC) with various cooling rates. The synchrotron X‐ray diffraction reveals that the polymorphous transition from cellulose (I) to cellulose (II) begins at NaOH concentration of 10 (wt%) and the complete transformation is obtained at the NaOH concentration of 15–20 (wt%) during the mercerization process. The Avrami equation was applied to depict the nonisothermal crystallization process and to analyze the experimental data of the composites. The DSC results show that the values of t1/2 for iPP/MCC (II) composites are lower than that for pure iPP. The polarized optical microscopy images reveal that the peculiar hybrid shish–calabash structure (HSC) with MCC (II) fibers serving as shish and iPP spherulites as calabash finally be formed. POLYM. COMPOS., 39:1064–1075, 2018. © 2016 Society of Plastics Engineers

Preparation of Esterified Bacterial Cellulose for Improved Mechanical Properties and the Microstructure of Isotactic Polypropylene/Bacterial Cellulose Composites.

Bacterial cellulose (BC) has great potential to be used as a new filler to reinforce isotactic polypropylene (iPP) due to its high crystallinity, biodegradability, and efficient mechanical properties. In this study, esterification was used to modify BC, which improved the surface compatibility of the iPP and BC. The results indicated that the cellulose octoate (CO) changed the surface properties from hydrophilic to lipophilic. Compared to the pure iPP, the tensile strength, charpy notched impact strength, and tensile modulus of the iPP/BC composites increased by 9.9%, 7.77%, and 15.64%, respectively. However, the addition of CO reinforced the iPP/CO composites. The tensile strength, charpy notched impact strength, and tensile modulus of the iPP/CO composites increased by 14.23%, 14.08%, and 17.82% compared to the pure iPP. However, the elongation at break of both the composites is decreased. The SEM photographs and particle size distribution of the composites showed improvements when the change of polarity of the BC surface, interface compatibility, and dispersion of iPP improved.

Flow-induced β-crystal of iPP in microinjection molding: effects of addition of UHMWPE and the processing parameters

The flow-induced β-crystal of isotactic polypropylene (iPP) with addition of ultrahigh molecular weight polyethylene (UHMWPE) molded by microinjection and influences of processing parameters on the formation of β-crystal in iPP/UHMWPE microparts were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). It was found that the contents and the dispersion of UHMWE affect the formation of β-crystal in iPP/UHMWPE blend. With the addition of UHMWPE, Kβ values of the blends increased significantly compared with that of the pure iPP and reached the maximum at the content of 2 wt% UHMWPE. In addition, a better dispersion of UHMWPE can facilitate the formation of the β-crystal in the iPP/UHMWPE. The results showed that the thermal stability of the β-crystal was enhanced with increasing the mold temperature. When the mold temperature was increased from 60 to 120 °C, the β-crystal become more perfect. High injection speeds can promote the formation of the β-crystal, but the value of the injection speed must be within a certain range.

Effect of Different Nucleating Agents on the Crystallization of Ziegler-Natta Isotactic Polypropylene

Ziegler-Natta isotactic polypropylene (iPP) was melt mixed with four different nucleating agents (carbon nanotubes (CNT), carbon nanofibers (CNF), lithium benzoate (LiBe), and a sorbitol derivative (Millad)) in order to study their effect on the crystallization of iPP. It was found that the four different nucleating agents promote the alpha crystalline form. At 0.01 wt%, the carbon nanoparticles produced the higher crystallization temperature “Tc” (~119°C), whereas, at 0.10 wt%, LiBe and Millad produced a markedly higherTc(~125°C).Tcof pure iPP was 111°C. With 0.1 wt% nucleating agent, at 120°C, the crystallization half-life time of PP, when using LiBe or Millad, was 15 times faster than for pure PP, whereas, when using carbon nanoparticles, it was 20–25 times faster. At 135°C, with 0.01 wt% nucleating agent, the isothermal crystallization process of iPP was completed after 25 min, as well as with Millad. With LiBe, it was completed after just 15 min and, with any of the carbon nanoparticles, it was practically over after only a couple of minutes.

Properties of isotactic polypropylene/atactic polypropylene blends

High-molecular-weight atactic polypropylene (HMW-aPP) was used as the impact modifier in isotactic polypropylene (iPP). HMW-aPP (M w 315,000 g/mol) was made by using metallocene catalysts, and iPP/HMW-aPP blends were prepared in a twin-screw extruder. The effects of HMW-aPP on the crystalline morphology, and thermal and mechanical properties of iPP were investigated by polarizing microscopy, differential scanning calorimetry, a universal testing machine, and Izod impact tests. The crystallization temperature and crystallinity of the iPP/HMWaPP blends increased compared to that of pure iPP. The HMW-aPP acted as a diluent during the crystallization of the iPP/HMW-aPP blends. These diluent HMW-aPP molecules prevented entanglement of the iPP molecules, which facilitated the crystallization of iPP. The Izod impact strength of the iPP/HMW-aPP blends increased with increasing HMW-aPP content owing to the incorporation of the soft HMW-aPP into the hard iPP. The Izod impact strength of the iPP-80 blend dramatically increased by 680% compared to that of neat iPP. Open image in new window