Mechanical Properties Of Isotactic Polypropylene Research Articles

Isolating the Effect of Crosslink Densities on Mechanical Properties of Isotactic Polypropylene Using Dissipative Particle Dynamics

AbstractGiven the importance of preserving the mechanical properties of recycled isotactic polypropylene (iPP) during its processing, this work provides an improved understanding of the contribution of introducing physical or chemical crosslinks using the dissipative particle dynamics (DPD) method, which makes it possible to model iPP structures with a realistic range of crosslink densities. First, the protocol to build a coarse‐grained model of iPP from an all‐atom expression by Bayesian optimization is described. A Bayesian optimization procedure employing two different cutoff distances successfully provides optimal DPD parameters reproducing iPP's properties compared to the all‐atom system. Then, the coarse‐grained iPP model with optimal DPD parameters is applied to study structures containing a realistic range of crosslink densities to evaluate their mechanical properties. These calculations demonstrate that the mechanical properties such as the Young's modulus and ultimate strength increase while the fracture strain decreases with an increase in the crosslink density, which is consistent with experimental observations. The results also show that there is a critical crosslink density above which these properties start to be improved due to the introduction of crosslinks. These findings can help us to obtain targeted properties of recycled iPP by introducing physical or chemical crosslinks.

Experimental Investigation of Effects of the Nucleating Agent on Mechanical and Crystallization Behavior of Injection-Molded Isotactic Polypropylene

In this study, we investigated the effect of talc (magnesium-silicate-monohydrate/3MgO.4SiO2.H2O) nucleating agent (NA) on the thermal and mechanical properties of isotactic-polypropylene (i-PP) at loadings ranging from 0.5 to 5% by weight using the melt compounding method. The results demonstrated that NA/i-PP exhibited significantly improved mechanical performance compared to neat i-PP. In addition, the influence of the concentration of the NA on the melting and crystallization behavior of neat i-PP was also analyzed through DSC curves. The tensile and flexural properties of i-PP enhanced as NA concentration increased. Furthermore, scanning electron microscopy revealed that there is a significant difference in the fracture surface between the NA/i-PP and the i-PP matrix. Consequently, it was determined that the NA (talc) used in this study was a good NA for i-PP, improved the mechanical and thermal properties of the product, affected the crystallization properties and the microstructure, and reduced the mold cycle time. Besides these, the use of various additives between talc and i-PP matrix that can improve interface features are expected to be an alternative approach to the new i-PP design with much higher mechanical and thermal properties.

In situ synthesis of calcium pimelate as a highly dispersed β‐nucleating agent for improving the crystallization behavior and mechanical properties of isotactic polypropylene

AbstractThe reaction precursors pimelic acid (Pi) and calcium stearate (CaSt) were added in situ during extrusion of isotactic polypropylene (iPP) to generate self‐dispersed calcium pimelate (CaPi[IS]). The results reveal that the nucleating agents (NAs) synthesized in situ obviously affected the nucleation effect in iPP. The crystallization, mechanical properties and melting behavior of nucleated iPP were investigated. The crystallization temperature (Tc) of iPP modified with CaPi(IS) increased by 4–5°C when compared to that of pure iPP. Especially, when the addition amount of CaPi(IS) in iPP was 0.30 wt%, the relative β‐crystal concentration of iPP/CaPi(IS) reached the highest level of 96.47%, 22.71% higher than that of iPP/CaPi. However, Pi and CaSt has hardly impact on the nucleation effect in iPP. The mechanical properties of iPP show that CaPi and CaPi(IS) have excellent toughening effect on iPP while Pi and CaSt greatly improved the stiffness of iPP. Furthermore, the dispersion of these NAs in iPP was investigated by scanning electronic microscope (SEM). It can be clearly seen that the CaPi(IS) particles are uniformly distributed in the iPP after magnification.

Suppression in Melt Viscosity of the Homogeneously Mixed Blends of Polypropylene (iPP–UHMWiPP) in the Presence of an Oxalamide

Here we report on the influence of an aliphatic oxalamide-based nucleating agent (OXA3,6) on the viscoelastic and mechanical properties of isotactic polypropylene (iPP) blended with ultrahigh molecular weight iPP (UHMWiPP). The linear viscoelastic properties are investigated by using a plate–plate rheometer; the presence of only 0.5 wt % of OXA3,6 in the iPP–UHMWiPP blends results in a reduction of the complex viscosity in the entire frequency domain examined. This observation holds irrespective of the UHMWiPP weight fraction, up to 25 wt %. The viscosity suppression is attributed to an acceleration of the reorientation times of the chains, especially the longer ones, due to partial alignment of their molecular segments. Furthermore, SAXS measurements on cooled, injection molded samples hint that OXA3,6-containing samples display enhanced alignment under processing conditions (injection molding). Compared to samples without OXA, an increase in the SAXS intensity along the equator is observed in the OXA3,6 samples, implying an enhanced ability of shish-kebab formation. Such a morphological development results in higher yield stress while maintaining the elastic behavior.

Mechanical Properties of Isotactic Polypropylene with Oriented and Cross-hatched Lamellae Structure

Abstract The mechanical properties of injection moulded unreinforced isotactic, polypropylene depend on the crystalline structure and lamellae orientation. Push-pull processing is an injection moulding technique that allows the user to produce parts with oriented structures. Mostly applied for short fibre reinforced thermoplastics in order to align fibres parallel to the flow direction, this technique can also be used to orient the polymeric matrix of LCP and polypropylene. A comparison of mechanical properties as well as investigations on morphology between the samples produced using conventional injection moulding and push-pull processing are presented trying to improve the knowledge about this so far rather unknown technique.

Effect of aromatic dihydrazide compounds on crystallization behavior and mechanical properties of isotactic polypropylene

Effect of aromatic dihydrazide compounds on crystallization behavior and mechanical properties of isotactic polypropylene

Calcium Salt of L-Isoleucine-Phthalate: An α-Nucleating Agent That Enhances the Crystallization Behavior and Mechanical Properties of Isotactic Polypropylene

In this study we prepared the novel compound L-isoleucine-phthalandione (LIPTA), featuring carboxyl and amide groups, and its calcium salt, the calcium salt of L-isoleucine-phthalate (LIPTA-Ca), and characterized them using 1H nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and differential scanning calorimetry (DSC). LIPTA-Ca has a relatively high melting point and thermostability. We employed DSC and polarized optical microscopy and tests of mechanical properties to examine the effect of LIPTA-Ca on the crystallization behavior and mechanical properties of isotactic polypropylene (iPP). We found that LIPTA-Ca is a highly effective α-nucleating agent that can increase the crystallization temperature of iPP by more than 10 °C during cooling, when present as an additive at a content of 0.15 wt%, while greatly decreasing the spherulite size and accelerating the crystallization rate of iPP. In addition, LIPTA-Ca can improve the rigidity of iPP significantly without decreasing its toughness.

Effect of the lanthanum and cerium phenylphosphonates on the crystallization and mechanical properties of isotactic polypropylene

In this article, the lanthanum phenylphosphonates (LaPPA2) and cerium phenylphosphonates (CePPA2) were synthesized and the effect on the crystallization conducts and mechanical performances of isotactic polypropylene (iPP) were studied. After adding 0.05wt% of LaPPA2 and CePPA2, the crystallization temperature enhanced appreciably. The polarized optical microscopy (POM) imagines indicated that the LaPPA2 and CePPA2 could accelerate the crystallization speed and reduce the spherulites sizes significantly. The presence of LaPPA2 and CePPA2 decreased appreciably the non-isothermal crystallization kinetics parameter F(T). Meanwhile, the nucleation efficiency of LaPPA2 and CePPA2 was similar to industrial standard NAs NA-11, HPN20E and HPN68L. In addition, the mechanical properties of iPP have been improved by adding LaPPA2 and CePPA2. According to the investigation of nucleated iPP viscoelasticity, it can be confirmed that the CH/π interplay between iPP and the aromatic groups of LaPPA2 and CePPA2 promoted the attachment of iPP helix and following nucleation.

Thermal and mechanical properties of biodegradable isotactic polypropylene

In this study, the effects of two different biodegradable plastic additives on the thermal and mechanical properties of isotactic polypropylene were investigated, analyzed, and presented. Biosphere biodegradable plastic additive and another oxidative biodegradable plastic additive, D2W, were used in 0.25, 0.5, 1.0, 1.5, and 2.0 wt% to prepare two sets of isotactic polypropylene composites. Differential scanning calorimeter and optical polarized light microscope were used to analyze the obtained composites thermally while the mechanical properties of these composites were studied by conducting tensile and impact testing. The morphological results reveal that only monoclinic α spherulites were obtained when the polypropylene crystallizes isothermally from the melt, it was found that both biodegradable plastic additives used decreases the size of the spherulites and increases their densities per unit volume. The incorporation of the Biosphere within the polypropylene matrix raises the crystallization temperature while the existence of D2W within the matrix delays the crystallization process. The addition of 2 wt% of Biosphere allows polypropylene to crystallize at about 13°C higher than neat polypropylene. It has been found that the addition of the biosphere increases Young’s modulus, while decreases the yield strength, the elongation at break, and the impact strength. On the other hand, D2W as an oxidative biodegradable plastic additive increases the elongation at break and the impact strength while decreases the yield strength and Young’s modulus.

Combined effect of chemically compound graphene oxide‐calcium pimelate on crystallization behavior, morphology and mechanical properties of isotactic polypropylene

AbstractThe combined nucleation effect of graphene oxide (GO) and calcium pimelate (CaPi) which are chemically compound together (expressed in GO − CaPi) in isotactic polypropylene (iPP) was investigated. Fourier transform infrared (FTIR), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA) verified that CaPi was chemically compound with GO by chelate bonds. The crystallization behavior and crystalline morphologies of iPP nucleated with different mass ratio of GO and CaPi were investigated. The crystallization peak temperature of iPP nucleated with 0.2 wt% GO − CaPi with the mass ratio of 1:5 (GO1 − C5) was increased by 8.3°C when compared with that of pure iPP, and the relative content of β‐crystal reached up to 0.7962. Whereas, the crystallization peak temperature of iPP nucleated with 0.2 wt% GO and CaPi which are blended together by mechanical force (expressed in GO + CaPi) with the mass ratio of 1:5 (GO1 + C5) was only increased by 5.0°C. It was attributed to that the aggregation of GO + CaPi caused the decrease of the crystallization peak temperature, while the GO1 − C5 uniformly dispersed in the iPP matrix. Unexpectedly, the relative content of β‐crystal of iPP nucleated with 0.02 wt% GO1 − C5 reached up to 0.8094, and the crystallization peak temperature was increased by 6.7°C compared with that of pure iPP. Meanwhile, the impact strength, tensile strength and heat deflection temperature of iPP nucleated with 0.02 wt% GO1 − C5 increased by almost 45.86%, 2.03% and 7.7°C, respectively. The iPP nucleated with GO1 − C5 obtained a balance between stiffness and toughness and the thermo‐mechanical property of nucleated iPP was improved.

Quantification of the Young's modulus for polypropylene: Influence of initial crystallinity and service temperature

ABSTRACTIn this study, the mechanical properties of isotactic polypropylene (iPP) materials with different crystallinities at room and elevated temperatures were investigated. In order to obtain samples with a certain range of crystallinity, and to ensure a uniform microstructure of these samples, the iPP samples obtained by injection molding required melt compression molding and controlled annealing. In the macromechanical studies, the experimental results showed that the storage modulus and Young's modulus of polypropylene were sensitive to the service temperature. The crystallinity also had a great influence on this relationship. A function was proposed to evaluate the dependence of the Young's modulus of polypropylene on initial crystallinity and service temperature, and tested based on experimental data. The Young's modulus of iPP is reduced by about 90% when the service temperature rises from 25 to 125 °C. Moreover, the reduced value in Young's modulus between polypropylene having the highest and lowest crystallinity was reduced from 214.55 to 56.75 MPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48581.

Synergistic nucleation effect of calcium sulfate whisker and β-nucleating agent dicyclohexyl-terephthalamide in isotactic polypropylene

The crystallization and melting behaviors and mechanical properties of isotactic polypropylene (iPP) containing a certain amount of stearic acid-modified calcium sulfate whiskers (S-CSW) and dicyclohexyl-terephthalamide (TMB-5) were investigated. The results revealed that S-CSW and TMB-5 had obvious synergistic nucleation effect in iPP. At the optimum addition concentration, the crystallization peak temperature of nucleated iPP increased by 8.1 °C compared with that of pure iPP, and the relative content of β-crystals in iPP reached to 0.9012. The impact strength, tensile strength and flexural modulus of iPP increased by approximately 61.8%, 1.71% and 26.1%, respectively, which were obviously better than that of iPP nucleated with S-CSW or TMB-5 independently.

Reinforcement of recycled PET for mechanical properties of isotactic polypropylene

Abstract For high-value use of recycled polyethylene terephthalate (r-PET) resource and simultaneous development of high performance isotactic polypropylene (PP) materials, the blends of r-PET with PP and its compatibilized versions were prepared. PP-g-MA, POE-g-MA and EVA-g-MA with same functional group, as well as their mixtures, were used as compatibilizer. The crystallization behavior, mechanical properties and microphotographs of r-PET/compatibilizer, r-PET/PP bleds and its compatibilized versions were characterized. The results indicated that addition of compatibilizer decreased the tensile and flexural strength of r-PET and slightly improve its impact strength. The introduction of r-PET to PP matrix increased the tensile and flexural strength of PP. The tensile and flexural strength of compatibilized r-PET/PP are dependent on the kinds of compatibilizers. Addition of PP-g-MA improved the tensile and flexural strength of r-PET/PP blends and introduction of POE-g-MA or EVA-g-MA increased the impact strength of r-PET/PP blends. Effect of compatibilizer and its mixtures and r-PET content on the mechanical properties of compatibilized r-PET/PP blends is discussed. The r-PET/PP blends with high strength and toughness can be obtained by compatibilization of the mixtures of PP-g-MA and POE-g-MA (or EVA-g-MA). This investigation provides an effective method to use the r-PET to prepare high performance PP blends with low cost and high-value.

Characterization of maleic anhydride/styrene melt-grafted random copolypropylene and its impact on crystallization and mechanical properties of isotactic polypropylene

Maleic anhydride/styrene-grafted random copolypropylene (MPP) was prepared by multi-monomer melt grafting. Fourier transform infrared spectroscopy verified that maleic anhydride and styrene were successfully grafted onto the polypropylene random copolymer (PPR) backbones. Dynamic rheological tests indicated the existence of long branched chains on MPP. The influence of grafting degree of maleic anhydride on the crystallization behavior of MPP was investigated by differential scanning calorimetry, wide-angle X-ray diffraction and polarized optical microscopy. The results showed that the crystallization rate of MPP was higher than that of PPR, and it increased with the increase in grafting degree. The long-chain branched structure could promote heterogeneous nucleation formation of MPP, resulting in the increase in crystallization rate and the decrease in spherulite size. Moreover, the effect of MPP content on crystallization and mechanical properties of isotactic polypropylene (PP)/MPP blends was further investigated. It was found that the interfacial interaction in the blends with 1–10 wt% of MPP was higher than PP/MPP-15% blend. Introducing MPP into PP could induce the formation of β-crystal. Consequently, the incorporation of MPP into PP increased the tensile strength and impact strength and maximum values were obtained for PP/MPP-10% blend.

Trap Distribution and Dielectric Breakdown of Isotactic Polypropylene/Propylene Based Elastomer With Improved Flexibility for DC Cable Insulation

In this paper, we report on electrical and mechanical properties of isotactic polypropylene (PP) blended with polyolefin elastomer (POE) and propylene-based elastomer (PBE). Carrier trap distribution of the samples was estimated by isothermal surface potential decay measurement, while dc breakdown strength was measured through a pair of semicircle electrodes. Elongation at break and tensile strength were obtained to examine the variation in mechanical property of PP caused by the addition of elastomers. Furthermore, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) have been employed to assist the understanding of morphology of the blends, thermal properties, and mechanical properties. Obtained results have indicated that with the increase of the elastomer content from 0 to 30 wt%, the trap depth appeared to be shallower and the dc breakdown strength tended to be reduced for both PP/PBE and PP/POE samples. Compared with PP/POE blend, PP/PBE blend had deeper trap depth, which should be responsible for its higher dc breakdown strength. In addition, PP/PBE blend has presented a better performance in elongation at break and tensile strength measurement. With the growth of the elastomer content, the crystallinity of the blends appeared to decrease, whereas the melting and the crystallization temperatures did not change remarkably. The SEM inspections and DMA results revealed better compatibility between PP and PBE compared with that between PP and POE, which should be the reason for the better electrical and mechanical properties of PP/PBE blend. The blend of PBE with low content could result in remarkably improved flexibility of PP with acceptable electrical strength for dc cable insulation.

Effect of injection molding parameters on crystallinity and mechanical properties of isotactic polypropylene

The effects of injection molding parameters namely mold temperature, melt temperature and injection speed on crystallization and mechanical properties of isotactic polypropylene were studied. The specimens were molded as per the Taguchi design of experiment and analyzed for signal to noise ratio and for analysis of variance test. The crystallinity and crystal sizes were determined by wide angle X-ray diffraction data. The specimens were tested for tensile, impact, flexural, stress relaxation and dynamic mechanical properties. It was observed that mold temperature was the most influential injection molding parameter governing the crystallinity and other mechanical properties. It was observed that increase in crystallinity is favorable from tensile and flexural strength point of view but impact properties deteriorate with increase in crystallinity. At high injection speed β-phase changes to α-phase due to shear induced orientation of polymer chains. It is interesting to notice that stress relaxation occurred in elastic as well as in plastic regions has the similar trends and can be modeled by the same decay model proposed in this paper.

Effects of analcime zeolite synthesized from local pottery stone as nucleating agent on crystallization behaviors and mechanical properties of isotactic polypropylene

This study reported the synthesis of analcime zeolite (AN‐zeolite) from a local pottery stone via hydrothermal method using 2 M NaOH at 120°C for 8 h in a Teflon‐lined stainless steel autoclave. The as‐synthesized AN‐zeolite was characterized for its phase composition, morphology, and particle size using X‐ray diffraction (XRD) analysis, scanning electron microscopy, and dynamic light scattering analysis, respectively. Subsequently, the AN‐zeolite was used as a nucleating agent for isotactic polypropylene (iPP). The prepared nucleated iPP was analyzed for its crystallization behaviors (by XRD, polarized optical microscopy, and differential scanning calorimetry), mechanical properties (impact strength and tensile properties), and morphology. It was found that the AN‐zeolite can induce to form a mass of α‐crystal and only a little β‐crystal in the iPP, along with the significant increase in the nuclei content, crystallization rate, and crystallization temperature, but a substantial decrease in the spherulite size. In addition, the incorporation of an appropriate amount of the AN‐zeolite into the iPP caused an increase in the impact strength (at 1.25 wt% optimal), tensile strength (at 1.25 wt% optimal), and Young's modulus (at 2 wt% optimal), but a deterioration of the elongation at break with increasing AN‐zeolite content compared with the neat iPP. J. VINYL ADDIT. TECHNOL., 24:E85–E95, 2018. © 2017 Society of Plastics Engineers

Phase transformation and mechanical properties of halloysite nanotubes‐modified isotactic polypropylene filaments

ABSTRACTPhase transformation and mechanical properties of isotactic polypropylene (iPP) with well‐distributed 0.3, 0.8, and 1.2 wt % halloysite nanotubes (HNTs) are studied. The spatial distribution of HNTs in the iPP matrix is analyzed using transmission electron microscopy and found to be homogeneously dispersed. Phase transformation from molten to solid states is characterized by polarized optical microscopy under an isothermal condition at different temperatures and differential scanning calorimetric in cooling and heating at different rates. Average size of spherulites, the degree of undercooling and total solidification time of iPP decrease as the amount of HNTs increases, suggesting HNTs act as nucleation sites for iPP. More interestingly, the wide‐angle X‐ray diffraction analysis only showed the formation of the α‐form iPP crystallites for the extruded filament, while kinetics results indicating the existence of β‐form crystals. These results together demonstrated the presence of HNTs leads to heterogeneous phase distribution which enhances the mechanical strength of the iPP filaments without reducing their ability for elongation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44714.

Influence of different beta-nucleating agents on the morphology of isotactic polypropylene and their toughening effectiveness

The influence of two 1,3,5-benzenetrisamide beta-nucleating agents in comparison to a commercial bisamide beta-nucleating agent on the morphological and mechanical properties of isotactic polypropylene (iPP) is presented. To complete the study, the neat iPP and iPP containing a 1,3,5-benzenetrisamide alpha-nucleating agent was investigated. To evaluate the effectiveness of the different supramolecular polymer additives with regard to their influence on the toughness of iPP, a difficult-to-toughen high melt flow rate (MFR) iPP grade was selected. Investigations by wide-angle X-ray scattering (WAXS) confirm that the two 1,3,5-benzenetrisamides and commercial beta-nucleating agent induce the beta crystal modification of the polymer, whereas only the alpha modification is observed for the neat polymer and the 1,3,5-benzenetrisamide alpha-nucleating agent. Scanning electron microscopy (SEM) pictures on etched samples clearly reveal a shish-kebab structure in beta-nucleated iPP with 1,3,5-benzenetrisamides. For these two samples, Charpy impact investigations show a pronounced increase in toughness, also compared to the commercial bisamide beta-nucleating agent.

Mechanical properties improvement of montmorillonite‐filled isotactic polypropylene nanocomposites by β‐modification

To investigate the effect of β‐crystallization on mechanical properties of isotactic polypropylene (iPP) nanocomposites, montmorillonite (MMT)‐filled α‐iPP and β‐iPP nanocomposites were prepared by MMT with α‐ and β‐nucleating surface, respectively. The polymorphic composition, mechanical properties and fracture morphologies of α‐MMT and β‐MMT filled iPP nanocomposites were compared and the exfoliation of MMT in the iPP matrix were investigated. It is found that the tensile modulus, yield strength, and flexural properties of β‐MMT filled iPP nanocomposites are higher than those of β‐iPP and the impact strength of β‐MMT filled iPP nanocomposites is higher than those of both β‐iPP and α‐iPP nanocomposites. The impact strength increases with increasing of the β‐crystal content. However, the β‐crystal content has little influence on the tensile and flexural properties of β‐MMT filled iPP nanocomposites. Compared with α‐MMT, the exfoliation of β‐MMT in iPP as well as interfacial adhesion between MMT and iPP are improved. POLYM. COMPOS., 38:E412–E420, 2017. © 2016 Society of Plastics Engineers