Crystallization Of Polypropylene Research Articles

Crystallization, orientation, and mechanical properties of laser-heated photothermally drawn polypropylene/multi-walled carbon nanotube fibers

Polypropylene (PP)/multi-walled carbon nanotube (MWCNT) fibers at MWCNT contents of 0, 0.5 and 1wt% were melt spun and photothermally drawn by irradiating them with a near-infrared laser during elongation. These fibers were then compared to hot-drawn PP/MWCNT fibers. The crystallinity of the photothermally drawn PP/MWCNT fibers was higher, whereas the degree of orientation of PP crystals was similar for both types of fibers. However, the degree of orientation of MWCNTs in the photothermally drawn PP/MWCNT fibers was higher, which was ascribed to the laser-induced local heating effect of MWCNTs dispersed in the polymer matrices. Higher breaking stress and modulus were obtained for the photothermally drawn PP/MWCNT fibers at the same MWCNT content. Therefore, laser-induced photothermal drawing has significant potential as a fiber-drawing method for enhancing the mechanical properties of the PP/MWCNT fibers.

CRYSTALLIZATION OF POLYPROPYLENE: APPLICATION OF DIFFERENTIAL SCANNING CALORIMETRY PART I. ISOTHERMAL AND NON-ISOTHERMAL CRYSTALLIZATION

A b s t r a c t: Theoretical background of the crystallization of isotactic polypropylene is summarized with respect to the potential of DSC method applied for the analysis of isothermal and non-isothermal processes.

The crystallization of polypropylene with reduced density of entanglements

The crystallization of polypropylene with different density of macromolecular entanglements was studied in isothermal and non-isothermal conditions. The growth rate of spherulites increased with reduced concentration of entanglements. Reduction of entanglements shifted the temperature of transition between Regimes II and III, which means that more regular growth of crystals was possible at lower temperature. The range of temperatures at which polypropylene cavitated in regions of melt occluded by spherulites was limited to 137–139°C, with weak dependence on entanglements density. DSC studies showed that isothermal crystallization is faster in less entangled polymers, however the crystallinity degree and long period of structure (by SAXS) were similar for studied materials. When the crystallization was completed during fast cooling, the differences between individual samples were more significant. The partial disentangling, overcoming some limitation for movements of macromolecules, made possible easier crystallization, even at low temperature of Regime III. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 748–756

Simultaneous enhancements of mechanical properties and hydrophilic properties of polypropylene via nano‐silicon dioxide modified by polydopamine

ABSTRACTThis study is focused on the development of high‐performance composite materials based on nano silicon dioxide (nano‐SiO2) modified by polydopamine (PDA). A facile one‐step method was developed to synthesize core–shell structured SiO2@polydopamine (PDA) nanospheres. During the synthesis, a PDA shell was simultaneously coated on the SiO2 nanospheres to form the core–shell nanostructure which was blended with polypropylene (PP) and β nucleating agent (β‐NA) to enhance both mechanical and hydrophilic properties. Nano‐SiO2 particles modified by PDA (SiO2@polydopamine) influence the crystallization of PP seriously. The results indicated that when 1%wt SiO2@polydopamine was added, the impact strength of composite reached the maximum value 12.60k J/m2 increasing 137% compared with PP, the bending strength and bending modulus decreased slightly reaching 41.85 MPa, and 2192 MPa, respectively, the composite possessed hydrophilic performance with the water contact angle of 88.32°. β nucleating agent was used in all formulations, the synergistic effect toward mechanical properties with SiO2@polydopamine was studied. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45004.

Mechanistic insights into the shear effects on isotactic polypropylene crystallization containing β-nucleating agent

The crystalline structures and crystallization behaviors of iPP containing β nucleation agent TMB-5 (iPP/TMB-5) were investigated by synchrotron radiation wide angel X-ray diffraction (SR-WAXD), differential scanning calorimeter (DSC) and polarized light microscope (PLM). It was found that α-crystallization lagged behind β-crystallization at normal temperatures, but the discrepancy reduced with increasing temperature. TMB-5 could not induce β-iPP when the nucleation agent is wrapped up with α-crystal that crystallized at high temperatures. The polymorphic composition of iPP/TMB-5 was susceptible to the introductory moment of shear. New crystallization process of β-nucleated iPP was proposed to understand the experimental phenomena which could not be explained by those reported in the literature. It was supposed that polymer crystallization initiated from mesophase, and the formations of iPP crystals involved the organization of helical conformation ordering within mesophase. It was proposed that the iPP melt contained mesophases with stereocomplex-type ordering of right-handed and left-handed helical chains which could be disturbed by shear or TMB-5, leading to different polymorphic structures.

Effect of montmorillonite on polypropylene crystallization

The effect of additions of pure and modified montmorrilonite on the polypropylene crystallization rate was studied within the framework of Avrami model. In the presence of these fillers in amounts of 2.5–5.0 wt %, both the crystallization rate and the degree of crystallinity increase, and at the content of these fillers increased to 10% and higher values these parameters decrease. Introduction of fillers enhances the mechanical properties of polypropylene, which allows the developed material to be recommended for the production of packaging film.

The relationship between crystal structure and nucleation effect of 1,3,5-benzenetricarboxylic acid tris(phenylamide) in isotactic polypropylene

1,3,5-Benzenetricarboxylic acid tris(phenylamide) (hereinafter called as “BTA-93”) was synthesized and proved to be a highly efficient α-crystalline nucleating agent through investigation of crystallization and melting behaviors of nucleated isotactic polypropylene (iPP) by differential scanning calorimetry. The optimum addition amount of BTA-93 in iPP was 0.07 wt%. At this low addition amount, crystallization peak temperature of iPP was increased from 119.3 °C of neat iPP to 126 °C and the nucleation effect was comparable to that of a highly effective commercial nucleating agent disodium bicyclo [2.2.1] heptane dicarboxylate (HPN-68) at addition amount of 0.2 wt%. Furthermore, the crystal structure of BTA-93 was obtained by single crystal X-ray diffraction. The crystal data indicated that the b-direction of BTA-93 crystal was about four times of 0.655 nm which was the cell edge of (010)iPP plane, and the lattice mismatch degree was 2.81%. The outstanding nucleation efficiency of BTA-93 in iPP could relate to the lattice matching between BTA-93 and α-iPP crystals.

The effect of organoclay and graphene on the crystallization of PP in ABS/PP blends

In the present research, the isothermal and non-isothermal crystallization of polypropylene (PP) phase in PP-rich poly(acrylonitrile–butadiene–styrene)/polypropylene (ABS/PP) blends was studied. The effect of nanofillers’ incorporation and specialty of organically modified montmorillonite (OMMT) and graphene, into the prepared blends on the isothermal and non-isothermal crystallization of PP phase, were investigated. Moreover, kinetic study of their isothermal crystallization process was carried out, by applying the Avrami equation. The addition of ABS to the PP matrix increased the crystallization rate of PP at 130 °C. The incorporation of OMMT in pure PP accelerated slightly the crystallization process, whereas in ABS/PP blends, it seemed to retard crystallization, due to interactions between ABS phase and organoclay. The incorporation of graphene in pure PP accelerated impressively its isothermal crystallization, while the addition of ABS in graphene/PP nanocomposite slowed down the crystallization rate of PP. The effect of ABS and nanofillers, separately or in combination, on the crystallization of PP phase was reflected on the kinetic parameters of the Avrami equation. Regarding the non-isothermal crystallization, ABS/PP blends presented higher crystallization temperature (T c) compared to pure PP. The organoclay reinforcement did not have any obvious effect on this temperature, whereas graphene caused significant increase, acting as nucleating agent. The presence of ABS to PP increased the concentration of the β-crystalline phase, reaching its maximum value at 30 mass% ABS content. The organoclay decreased the β-PP in ABS/PP blends, whereas graphene eliminated it.

Coupling of Multiscale Orderings during Flow-Induced Crystallization of Isotactic Polypropylene

The sequence and coupling of intra- and interchain orderings in flow-induced crystallization (FIC) of partially cross-linked isotactic polypropylene (iPP) is studied with in situ Fourier transform infrared spectroscopy (FTIR) and synchrotron radiation X-ray scattering techniques, which reveal that multiscale structural intermediates emerge prior to the onset of crystallization. Upon imposing flow, intrachain conformational ordering or coil–helix transition (CHT) occurs first, which is directly correlated with external stress. As helical content is built up at large strain, density fluctuation happens, and sufficient long helices may result in orientation ordering before FIC. The results demonstrate that stress induced intrachain CHT is the essential structural intermediate in FIC, which can be further coupled with interchain orientation and density providing either helical content or length meets the criterions for the phase transitions. We propose that coupling among external stress, intrachain conformat...

Chain Folding in Main-Chain Liquid Crystalline Polyester with Strong π–π Interaction: An Efficient β-Nucleating Agent for Isotactic Polypropylene

The influence of the main-chain liquid crystalline polyester (PBDPS) on the crystallization and melting behaviors of isotactic polypropylene (iPP) has been investigated by differential scanning calorimetry (DSC), X-ray diffraction (WAXD), and polarized optical microscopy (POM). The results suggested that PBDPS is an efficient β-nucleating agent for iPP. The melting crystallization temperature as well as β-crystal of iPP increased with increasing of PBDPS content. The relative content of β-iPP crystals (kβ) can reach 96.6% while adding 4% PBDPS during isothermal crystallization at 135 °C. The increased β-nucleation efficiency was ascribed to the adjacent phenyl rings in side groups of PBDPS stacked well together even when the temperature was higher than its clearing point (Ti). Moreover, the distance between stacked phenyls is 0.32 nm, which is half of the unit cell parameter in the c-direction of β-iPP, indicating a lattice match between β-iPP and PBDPS.

Oriented crystallization of long chain branched polypropylene induced by step-shear deformation in pre-crystallization regime

The oriented crystallization of long chain hyper-branched polypropylene (LCB-PP) induced by shear deformation in the pre-crystallization regime was investigated through simultaneous time-resolved synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS) measurements and compared with that of linear PP (L-PP). Highly oriented crystallization was induced in LCB-PP by the application of a step-shear in the pre-crystalline regime; in contrast, the crystalline lamellae of L-PP were slightly oriented. In addition, LCB-PP formed daughter lamellae whose a-axis was oriented along the shear direction. The oriented crystallization of LCB-PP induced by the step-shear was related to its primary structure in the following manner. Since the existence of branched chains increased the relaxation time of the LCB-PP chains, the elongated LCB-PP chains were remained for longer after the step-shear deformation. In addition, the branching points of LCB-PP aided the formation of point-like precursors for crystallization. Consequently, these point-like precursors were arrayed along the shear direction and transformed into thread-like precursors. This caused the rapid formation of highly oriented shish-kebab structures. Furthermore, since short chains that caused the formation of daughter lamellae were covalently tethered to the kebab parts in LCB-PP, the growth of the daughter lamellae were spatially restricted owing to which the a-axis of the daughter lamellae in LCB-PP was oriented along the shear direction.

Effect of Quinacridone Pigments on Properties and Morphology of Injection Molded Isotactic Polypropylene

Two quinacridone pigments were added (0.01; 0.05; 0.1; 0.5; 1; 2 wt%) to isotactic polypropylene (iPP), and their influence on mechanical and thermomechanical properties were investigated. Complex mechanical and thermomechanical iPP properties analyses, including static tensile test, Dynstat impact resistance measurement, and hardness test, as well as dynamic mechanic thermal analysis (DMTA), were realized in reference to morphological changes of polymeric materials. In order to understand the differences in modification efficiency and changes in polymorphism of polypropylene matrix caused by incorporation of pigments, differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) experiments were done. Both pigments acted as highly effective nucleating agents that influence morphology and mechanical properties of isotactic polypropylene injection molded samples. Differences between polypropylene samples nucleated by two pigments may be attributed to different heterogeneous nucleation behavior dependent on pigment type. As it was proved by WAXS investigations, the addition of γ-quinacridone (E5B) led to crystallization of polypropylene in hexagonal phase (β-iPP), while for β-quinacridone (ER 02) modified polypropylene no evidence of iPP β-phase was observed.

Crystallization behaviors and mechanical properties of carbon fiber-reinforced polypropylene composites

In this work, carbon fiber (CF)-reinforced polypropylene (PP) composites were prepared by melt processing with maleic anhydride-grafted polypropylene as compatibilizer. The mechanical properties and crystallization behaviors of the resulting composites were investigated detailedly. The interfacial compatibility of CRP composites was fine and CF dispersed in PP matrix homogeneously. CF played a nucleation agent for the crystallization of PP. The crystallization temperature increased with increasing CF content. Carbon fibers could act as the heterogeneous nucleation agent for PP, which would decrease the activation energy of crystallization, shorten the crystallization time and raise the crystallization rate dramatically. The original spherulite morphology of neat PP was also destroyed by CF. CF exhibited obvious reinforcing effects on PP matrix and improved the mechanical properties of PP materials. The tensile strength and flexural strength were increased over 100% with 20 mass% CF.

Comparative study of crystallization and lamellae orientation of isotactic polypropylene by rapid heat cycle molding and conventional injection molding

Abstract The crystallization and orientation of isotactic polypropylene (iPP) molded by rapid heat cycle molding (RHCM) and conventional injection molding (CIM) were studied. Due to the varying cooling rates and shearing, the molded parts exhibited a multilayered structure (skin, shear and core) across the part thickness, reflecting different degrees of crystallization and lamellae orientation of iPP. The morphology evolution of RHCM products was discussed based on the comparative research of morphology and structure at multiple sites on the RHCM and CIM specimens. Scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD) were used to analyze the thickness, crystallinity and lamellae orientation of these three distinct layers. The crystallization and lamellae orientation of iPP correlated strongly with the multilayered structure. In the RHCM process, one side of the mold is equipped with the rapid heat cycle function. The thickness and lamellae orientation next to the heated surface were less than that of the opposite skin layer without heating. Meanwhile, the crystallinity was greater than that of the opposite skin layer.

Control of Chain Orientation in Blends of Polypropylene and Polybutene‐1

An extruded sheet having unique molecular orientation is developed using a miscible blend of isotactic polypropylene (PP) and isotactic polybutene‐1 (PB). Blends containing a small amount of N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide are extruded from a ribbon‐shaped die onto a chill roll at various temperatures. It is found that form‐I crystals of PB become oriented in the flow direction, whereas β‐form crystals of PP become oriented perpendicular to the flow direction. The molecular orientation is the most obvious for the blend containing 60 wt% of PB extruded at a chill roll temperature of 80 °C. The anisotropy in the tensile modulus of the obtained extruded sheet is reduced by its extraordinary molecular orientation. image

Crystallization and melting characteristics of iPP nucleated by a sustainable eggshell powder-supported β-nucleating agent

The β-form crystals in isotactic polypropylene (iPP) are proved to be favorable and effective for developing general iPP plastics with high performance. Herein, sustainable eggshell power decorated with calcium pimelate (DES), an effective β-form nucleating agent for iPP, was fabricated via the interaction between pimelic acid and Ca2+ on the surface of eggshell powder at elevated temperature. DSC and FTIR analysis identified the reaction occurred and formation of calcium pimelate on surface of the eggshell powder. Then, the effects of the functionalized eggshell powder on the nonisothermal and isothermal crystallization behavior, melting characteristics and polymorph structures were investigated. From the nonisothermal crystallization experiments, the incorporation of supported β-form nucleator greatly enhanced the crystallization temperature of iPP. The content of β-form crystals (Kβ) could reach a value as high as 87% at 5 mass% DES load. Moreover, the crystallization and melting characteristics of iPP nucleated by DES were not changed under multiple scan conditions with melt temperature range from 190 to 250 °C. Interestingly, from the investigation of isothermal crystallization and subsequent melting behavior, it was found that DES is a temperature-dependent selective nucleator for inducing iPP crystallization. Main α-form crystals or β-form crystals could form when using high or low crystallization temperatures, respectively. Particularly, these results demonstrated a possibility to tailor the ratio of α-form crystals to β-form crystals by simply choosing isothermal crystallization conditions. Then the crystallization mechanism based on thermodynamics and kinetics factors was further discussed.

Effects of melt structure on non-isothermal crystallization behavior of isotactic polypropylene nucleated with α/β compounded nucleating agents

In this study, the effects of melt structure (tuned by controlling the fusion temperature Tf) on non-isothermal crystallization and subsequent melting behaviors of isotactic polypropylene (iPP) nucleated with α/β compounded nucleating agents (α/β-CNAs) have been further investigated. The results show that under all cooling rates studied (2–40°C/min), the crystallization temperature on cooling curves increased gradually with decrease of Tf, meanwhile, when Tf was in temperature range of 166–179°C where ordered structures survived in the melt (defined as Region II), crystallization activation energy ΔE was found to be evidently lower compared with that when Tf>179°C or Tf < 166°C. The results of subsequent heating showed that occurrence of Ordered Structure Effect can be observed at all the cooling rates studied; the location of the Region II was constant when cooling rate varied; Low cooling rate encouraged formation of more β-phase triggered by ordered structure. Moreover, the role of ordered structure on β-α recrystallization was comparatively studied by tuning the end temperature of recooling (Tend) after held at Tf, and it was found that ordered structure encouraged the formation of β-phase with high thermal stability at low temperature part of Region II, while enhanced the β-crystal with relatively low thermal stability at high temperature part of Region II. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Nucleation of crystallization of isotactic polypropylene in the gamma form under high pressure in nonisothermal conditions

The crystallization of isotactic polypropylene (PP) in γ-modification, which forms under high pressure but also at high temperature, can be nucleated by nucleating agents used for PP α-modification crystallizing under atmospheric pressure, like poly(tetrafluoroethylene) (PTFE) particles and commercial Hyperform HPN-20E. The study focuses on answering the question whether these nucleants are sufficiently active under high pressure to nucleate crystallization of PP during cooling in the temperature range of crystallization of the γ-form. To this aim, neat PP and PP with 0.2wt% of nucleating agents were annealed at 250°C for 5min and subsequently cooled under a pressure ranging from 1.3 to 300MPa. After releasing pressure, the specimens were analyzed by DSC, WAXD and PLM to have an insight into morphology, crystallinity and content of crystallographic forms. Both, Hyperform HPN-20E and PTFE, nucleated the crystallization of PP during cooling under high pressure in the γ-form causing an increase of crystallization temperature, the γ-form content and a decrease of grain size, although the first nucleant was more efficient. Calcium pimelate, a known nucleant of the β-form, studied for comparison, was ineffective.

Nucleation induced by “Short-Term Pressurization” of an undercooled isotactic polypropylene melt

Nucleation of semi-crystalline polymers is very sensitive to perturbations of the melt state. In contrast to the case of flow, the influence of pressure changes on nucleation has been almost neglected so far. In this work we explore the effect of the pressure history on isotactic polypropylene crystallization by applying a brief step-like increase of pressure to the undercooled melt. Using dilatometry and synchrotron X-ray diffraction, an enhancement of crystallization kinetics proportional to the magnitude of the pressure pulse is revealed. This acceleration is linked to an increase of the number of active nuclei after the short term pressurization, as confirmed by ex-situ optical microscopy observations. Up to an order of magnitude increase in nucleation density is found, for pressure pulses around 600–700bar. The pressure-induced nucleating effect is interpreted in the light of classical nucleation theory; although a non-classical “barrier-less” nucleation mechanism is also envisaged.

Analysis of flow induced crystallization through molecular stretch

Abstract In this work, specific experiments on an isotactic polypropylene are carried out, aiming to investigate the flow induced crystallization and the final morphology. The viscoelastic nature of the polymer is described by a non-linear Maxwell model applied to the conformation tensor. Shear stress evolutions, recorded during step shear isothermal experiments, are satisfactory described considering the molecular stretch, i.e. the difference between the two main eigenvalues of the conformation tensor. In the general model, the effect of temperature, pressure, and crystallinity are taken into account. Furthermore, a modeling framework is proposed to describe flow-induced crystallization of isotactic polypropylene. The spherulitic growth rate is analyzed on the basis of a flow dependent equilibrium melting temperature, using the molecular stretch as the key parameter. A phenomenological correlation of the nucleation rate with growth rate is observed. By combining the morphological models, both for nucleation and growth rate, for flow induced crystallization is possible to explain the effect of shear rate and shearing times in different experimental results, and potentially in the simulation of polymer processing.