Crystallization Of Polypropylene Research Articles

Exploring the effect of cooling rate on non-isothermal crystallization of copolymer polypropylene by fast scanning calorimetry

Exploring the effect of cooling rate on non-isothermal crystallization of copolymer polypropylene by fast scanning calorimetry

Visualization of Recrystallization Induced by Ultraviolet Degradation of a Polypropylene Film Using Raman Imaging.

Raman images were constructed for polypropylene (PP) films before and after ultraviolet (UV) irradiation (100 mW, 248-436 nm) for 10 h using several intensity ratios of Raman bands that are sensitive to crystallization of PP. In the images of PP films before the irradiation the intensity ratios are nearly uniform for the films but for those of the PP films after the irradiation, the ratios become large with a mottled pattern, indicating that recrystallization occurs in the PP films upon the irradiation of the UV light. The UV-irradiated PP films show worm-like shaped structures in few micrometer order representing the recrystallization of PP. The temperature gradient of PP is low (273 K), and thus, it is very likely that due to UV energy and polymer fragmentation, PP molecules become more mobile and some parts of molecular chains in amorphous parts of PP molecules lead to their rearrangement and recrystallization. In this study, we demonstrate that Raman imaging clearly detects subtle changes in the crystallinity with a micrometer order structure which morphological images cannot observe.

Preparation of Open-Cell Long-Chain Branched Polypropylene Foams for Oil Absorption.

This study aimed to prepare open-cell foams using a blend of long-chain branched polypropylene and polyolefin elastomer (LCBPP/POE) for the production of reusable oil absorbents. The supercritical CO2 foaming process was conducted using a two-step batch rapid depressurization method. This unique two-step foaming approach significantly expanded the temperature and pressure windows, resulting in more uniform cells with smaller sizes, ultimately leading to higher expansion ratios and an increased open cell content. The foaming process was optimized by adjusting parameters, such as the LCBPP/POE ratio, foaming temperature, and foaming pressure, reaching a maximum open cell content of 97.6% and a maximum expansion ratio of 48. The influence of polypropylene (PP) crystallization was investigated with the aid of scanning electron microscopy and differential scanning calorimetry. Furthermore, the hydrophobic and lipophilic characteristics of the LCBPP/POE open-cell foam were determined via contact angle measurements and oil/water separation tests. Oil absorption tests revealed that the blended LCBPP/POE foam has a higher oil absorption capacity than that of the pure LCBPP foam. The cyclic oil absorption tests demonstrated the outstanding ductility and recoverability of the LCBPP/POE open-cell foam in comparison to those of the pure LCBPP foam. Over 10 cycles, the LCBPP/POE foam maintained a substantial adsorption capacity, retaining 99.3% of its initial oil absorption capacity. With its notable features, including a high open cell content, excellent hydrophobic and lipophilic characteristics, superior oil absorption capacity, impressive cyclic oil absorption performance, and robust reusability, LCBPP/POE open-cell foams exhibit significant promise as potential oil adsorbents for use in oil spill cleanup applications.

The effect of expanded graphite and paraffin wax on the morphological, thermal, and rheological properties of PP/EVA blend

The study investigated the effect of paraffin wax, expanded graphite, and their dispersion on the properties of the blend of polypropylene (PP) and ethylene vinyl acetate (EVA). The idea is to reduce interfacial tension in blends of PP and EVA while enhancing the properties of blends in the process. The chosen optimum contents of the paraffin wax and EG in the 80/20 PP/EVA blend were 10 and 6 wt.%, respectively. The morphological features show that the expanded graphite (EG) particles had high affinity for each other. Moreover, EG filler particles are localized inside the minor EVA phase and some at the interface. Rheological properties revealed that the flow of the binary composites increased when 10 wt.% wax is added suggesting that wax enhanced the processability of the composites. The Cole-Cole plots deviated from the semi-circular arc suggesting heterogeneity in the blend and PP/EVA/Wax/EG composite. The addition of paraffin wax and EVA delayed crystallization of PP, while earlier crystallization of PP was promoted by the presence of EG. Generally, all samples caught fire after 10 s, started dripping and are thus given a V-2 rating according to the Underwriters Laboratories test standard 94 results (UL-94).

Polypropylene Color Masterbatches Containing Layered Double Hydroxide Modified with Quinacridone and Phthalocyanine Pigments-Rheological, Thermal and Application Properties.

Polypropylene color masterbatches containing modified layered double hydroxides, LDHs, were created. The simple, industry-acceptable method of LDH surface modification with quinacridone and phthalocyanine pigments using the pulverization method in ball mills was applied. It was reported that the modification parameters such as time and rotational speed affected the tendency to create the aggregates for modified fillers. TGA analysis of the modified LDH showed that modification with phthalocyanine pigment shifted the temperature at which 5%, T5%, and 10% of mass loss, T10%, occurred compared with that for unmodified LDH. The viscoelastic properties of prepared masterbatches were investigated. The incorporation of the modified fillers instead of neat pigments led to an increase in the loss shear modulus, G″, indicating a stronger influence on the dissipation of energy by the melted masterbatch. The similar values of tan, δ, were determined for melted masterbatches containing phthalocyanine pigment and green modified LDH filler. The incorporation of both LDHs modified by phthalocyanine and quinacridone pigment fillers slightly increased the zero-shear viscosity, η0, compared with that of the masterbatches based on the neat pigments. The Cole-Cole plots and the analysis of the Maxwell and continuous relaxation models showed that modified colored LDH fillers facilitated the relaxation of the melted masterbatch, and shorter relaxation times were observed. The phthalocyanine-modified LDH filler improved the thermal stability of the masterbatches. Additionally, the impact of pigments and modified, colored LDH on the crystallization of polypropylene was investigated.

Crystallization, structure and properties of PP-b-PE block copolymer

In recent years, a commercialized polypropylene (PP) and polyethylene (PE) block copolymer has been synthesized using chain-shuttling polymerization, but its molecular structure and properties are still limitedly understood. In this work, we analyzed the chain composition, mechanical properties, and structural transformations occurring during the deformation of commercial PP-PE block copolymer obtained via chain-shuttle technology. The chain composition and crystallization properties of PP-PE block copolymers obtained by chain shuttling technique were analyzed using nuclear magnetic resonance (NMR), temperature-rising elution fractionation (TREF), and differential scanning calorimetry (DSC) techniques. The sample has a mass ratio of 49:51 of PE chains to PP chains, but the crystallinity of the two components differs significantly. The PP displays limited crystallinity, indicating short PP chain segments. Some PE sequences are incorporated into the PP matrix as random copolymers, resulting in elastomeric behavior. We investigated the In-situ structural changes of crystals during stretching using synchrotron radiation 2D X-ray diffraction/scattering. In the elastic deformation region, the strain has a significant influence on the orientation of PE crystals but has little effect on the orientation of PP crystals. After the yield point, the strain-induced PE crystal failure resulting in a decrease in stress. In the strain hardening region, the orientation of PE induces recrystallization, forming a layered structure with tensile orientation. At the same time, the PP crystals are disoriented under the action of strain until they break. The results from this work provide significant insight into the design of PP-PE block copolymer products to meet the performance requirements needed for engineering applications.

How open‐stage melt crystallization affects tensile and shrinkage properties of 3D printed polypropylene

AbstractMelt crystallization of isotactic Polypropylene (PP) on open platform during 3D processing is critical and often challenging. Numerous factors that influence the melt extrusion of PP directly influence its crystallization and hence impact the physico‐mechanical properties of the printed parts. The present article represents a detailed investigation of the influence of 3D processing parameters on tensile and shrinkage properties of PP subject to respective melt‐crystallization behaviors. Moreover, the article also demonstrated the best experimental conditions that can produce mechanically stronger parts (even stronger than compression molded specimens used for comparison) with minimum warping. Influence of print temperature, bed temperature, print layer thickness (when the layer thickness varies by a margin of four folds), print orientation (horizontal or vertical), and infill rates was found to be highly sensitive towards melt crystallization of the PP dumbbell (which was printed as a product) hence brought about the highest variation in tensile and shrinkage properties. A print head temperature of above 220°C and a bed temperature of 60°C produced stronger dumbbells when printed with a higher layer thickness (0.20 mm/0.25 mm) in horizontal conditions with a 100% infill rate. Such specimens possessed higher tensile strength, and elongation at break values than the compression molded sample.

Polypropylene Nanocomposites Attained by In Situ Polymerization Using SBA-15 Particles as Support for Metallocene Catalysts: Effect of Molecular Weight and Tacticity on Crystalline Details, Phase Transitions and Rheological Behavior.

In this study, nanocomposites based on polypropylene are synthesized by the in situ polymerization of propene in the presence of mesoporous SBA-15 silica, which acts as a carrier of the catalytic system (zirconocene as catalyst and methylaluminoxane as cocatalyst). The protocol for the immobilization and attainment of hybrid SBA-15 particles involves a pre-stage of contact between the catalyst with cocatalyst before their final functionalization. Two zirconocene catalysts are tested in order to attain materials with different microstructural characteristics, molar masses and regioregularities of chains. Some polypropylene chains are able to be accommodated within the silica mesostructure of these composites. Thus, an endothermic event of small intensity appears during heating calorimetric experiments at approximately 105 °C. The existence of these polypropylene crystals, confined within the nanometric channels of silica, is corroborated by SAXS measurements obtained via the change in the intensity and position of the first-order diffraction of SBA-15. The incorporation of silica also has a very significant effect on the rheological response of the resultant materials, leading to important variations in various magnitudes, such as the shear storage modulus, viscosity and δ angle, when a comparison is established with the corresponding neat iPP matrices. Rheological percolation is reached, thus demonstrating the role of SBA-15 particles as filler, in addition to the supporting role that they exert during the polymerizations.

An Unconventional Route for Synthesis and Solid-State Processing of Low-Entangled Ultra-High Molecular Weight Isotactic Polypropylene.

Introducing the reverse micelle formation during polymerization, and thus avoiding the catalyst support, aggregated single crystals of ultra-high molecular weight isotactic polypropylene having spherical morphology are obtained. The ease in flowability of the spherical nascent morphology, having a low-entangled state in the non-crystalline region of the single crystals in the semi-crystalline polymer, allows the sintering of the nascent polymer in the solid state without melting. Thusmaintains a low-entangled state, and facilitates the translation of macroscopic forces to macromolecular length scale, without melting, leading to the formation of uniaxially drawn objects having unprecedented properties that can be used in the development of one component, high-performance, easy-to-recycle composites. Thus having the potential of replacing difficult-to-recycle hybrid composites.

The Influence of Glass Fiber/Glass Fiber Powder with β-Nucleating Agent on the Properties of Polypropylene

Glass fiber-reinforced polypropylene (PP/GF) has been widely used due to its high stiffness, but for some applications that need low-module characteristics, PP/GF will have limitations due to its lower toughness, so it is necessary to develop glass fiber-modified polypropylene with good stiffness–toughness balance performance. In this study, two average length glass fibers (4.5 mm and 12 mm) and glass fiber powder, combined with β-nucleating agent, were used to investigate the effects on the crystallization and mechanical properties of polypropylene. The results show that compared with glass fiber, glass fiber powder cooperates with β-nucleating agent reinforced polypropylene composite showed good stiffness–toughness balance performance, and β-crystals were found in the composite measured by Differential Scanning Calorimetry (DSC), the presence of β-crystals can improve the toughness of the composite.

Nanolignin as Nucleating Agents Promoting Crystallization of Isotactic Polypropylene

Lignin is the second most abundant pollution-free biomass material. However, most of lignin is discarded as waste in river or burned as fuel, which results in serious environmental pollution problems and low utilization efficiency of lignin at present. Thus, high-value utilization of lignin has become a hot research field. Herein, nanolignin (nano-Lig) is prepared successfully by the self-assembly method, and then nano-Lig and isotactic polypropylene (iPP) are mixed to prepare a series of nano-Lig/iPP composites by the solution blending method. Nano-Lig not only enhance thermostability of iPP but also improve crystallization properties of iPP. When 1.0 wt% nano-Lig was added in iPP, the crystallinity of iPP increased by 6.39% compared to iPP. Nano-Lig can increase the crystallization rate of iPP through investigation of kinetics of nonisothermal crystallization, suggesting nano-Lig can be used as a nucleating agent for iPP.

Morphological evolution ofTMB‐5/ethylene–vinyl alcohol copolymer blends under biaxial‐stretching field and its effect on the crystallization and gas barrier properties of isotactic polypropylene

AbstractThe morphological evolution of TMB‐5/ethylene–vinyl alcohol (EVOH) copolymer blends under biaxial‐stretching field and its effect on the crystallization and gas barrier properties of isotactic polypropylene (iPP) were investigated. iPP/TMB‐5/EVOH ternary blends with TBM‐5 selectively distributed in the EVOH phase were prepared through a multistage stretching extrusion, which combined an assembly of layer multiplying elements (LMEs) with an extruder. Scanning electron microscopy revealed that the biaxial‐stretching field in LMEs transformed the TMB‐5/EVOH phase into platelets along the extrusion direction. Differential scanning calorimetry and X‐ray diffraction results indicated that the TMB‐5 particles were distributed in the EVOH phase and noβcrystals formed in as‐extruded samples. Especially, the TMB‐5 was released from the EVOH phase into iPP in the annealing process and induced the formation ofβcrystals. Compared with that of pure iPP, the oxygen permeability coefficient of iPP containing aligned TMB‐5/EVOH platelets decreased more than three times. The enhanced barrier properties resulted from the increased tortuosity of the diffusion pathway caused by the orientated high‐aspect‐ratio platelets. © 2023 Society of Industrial Chemistry.

Enhanced breakdown strength of the BaTiO3/polypropylene nanocomposite film based on the biaxial stretching process

AbstractThe significant progresses of polymer‐based nanocomposites with improved dielectric performances are urgently calling for an effect way to realise commercial production. Up to now, the biaxial stretching technology is still a powerful method to produce the high‐performance dielectric films applied in the film capacitors due to its full‐blown applications. In this work, a classical composite system of BaTiO3/polypropylene was applied to reveal the connection between the microstructure changes and dielectric properties of the corresponding nanocomposite films in the biaxial stretching process. The permittivity of BT‐30 wt% nanocomposite reached 2.8 at 103 Hz after stretching, and its breakdown strength reached 340 MV/m. In addition, the breakdown strength of BT‐10 wt% nanocomposite could even be promoted to 452 MV/m, which was 1.3 times higher than that before stretching. The microstructure test demonstrated that the rearrangement of nanofillers, high crystallinity and the oriented polypropylene crystals were advantageous to the improvement of breakdown strength for the stretched nanocomposite films. Therefore, the application of biaxial stretching technology into the preparation of nanocomposite dielectric film is an enormous potential way for the energy storage film capacitors.

Ethylene Comonomer-Directed Epitaxial Nucleation and Growth of β-Nucleated Isotactic Polypropylene

We present a molecular-level investigation of the epitaxial crystallization of β-nucleated isotactic polypropylene associated with the minor and local topographic modification at the interface, i.e., the inclusion of an ethylene comonomer. The experimental results show that the relative fraction of β-crystal (Kβ) decreases progressively with increasing the amount of ethylene comonomer, which originates from a simultaneous reduction in the β-nucleation ability of a β-nucleating agent (N,N′-dicyclohexylterephthalamide, DCHT) toward propylene–ethylene random copolymers (PERs) and the growth rate of the β-crystal relative to the α-crystal. With the aid of molecular mechanics simulation, we demonstrate that such a topographic modification weakens the intermolecular interactions at the nucleation and growth interfaces, thereby modifying the epitaxial nucleation of the β-crystal and the growth kinetics of β- and α-crystals. The study reveals that the polymorph selection of the PERs/DCHT system is not solely determined by the lattice match but also profoundly influenced by the topography characteristics dependence of molecular interaction at the crystalline interfaces. Our fundamental insight could have important implications in the control of the polymorphism of polymers through the careful design of the topography of the nucleation and growth interfaces.

Compatibilization of polypropylene/high‐density polyethylene blends using poly(propylene‐co‐ethylene)

AbstractTernary blends of polypropylene (PP), high‐density polyethylene (HDPE), and a random copolymer with 85% propylene and 15% ethylene (trade name Vistamaxx 6202, abbreviated here as VM) have been investigated to elucidate the efficiency of this additive in the management of recycling streams. Differential scanning calorimetry showed that VM will induce simultaneous crystallization of PP and HDPE. Polarized Optical Microscopy revealed a breakdown in the spherulitic structure already at 10% of additive (for blends with ratio PP: HDPE = 1:1), respectively 17%, (for PP/HDPE = 7:3). A similar threshold was found in the impact strength, and stress–strain‐curves. This means that VM is also advantageous for recycling of PP: HDPE blends, especially those with high PP content.

Crystallization and melting kinetics of low tacticity polypropylene in relation to preformed nuclei and uncrystallizable defects

Fast scanning calorimetric experiments were carried out on low-isotacticity polypropylene (LT-PP) to evaluate the effect of pre-nucleation below the glass transition temperature (also known as Tammann's crystal nuclei development method) on the kinetics of crystallization and melting. The melting kinetics of secondary crystallized LT-PP was not affected by the presence of crystal nuclei, although the isothermal crystallization rate of LT-PP was accelerated by increasing the amount of crystal nuclei. The maximum primary crystallization decreased with increasing amounts of crystal nuclei. This behavior can be explained by the formation of uncrystallizable defects between the crystalline domains.

Processing and Characterization of Polypropylene Nanocomposite Films Reinforced with Hexagonal Boron Nitride Nanosheets

In this study, we synthesized hexagonal boron nitride nanosheets (h-BNN) via the molten hydroxide exfoliation method which results in small flakes and nanoscrolls. The resultant h-BNNs can be dispersed in various solvents such as water, ethanol, and acetone, and form a stable dispersion. The morphological and structural analysis of h-BNNs were performed with Fourier Transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and scanning electron microscopy (SEM). The masterbatch (MB) method was used to incorporate the h-BNNs into the polypropylene (PP) matrix via melt mixing. Dilution and film production processes were performed using a twin screw extruder. Nanocomposite films having an h-BNN weight ratio of 1%, 2%, 3%, and 5% were prepared. Thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC) were used to investigate the thermal stability. Crystallization (Tc) temperatures were increased with the increased amount of h-BNNs and h-BNNs nucleating agent behavior on the PP crystallization was observed. Oxidation induction time (OIT) of the pure PP was increased from 8.84 min to 17.82 min. The results show a considerable effect of the h-BNN content on the thermo-oxidative stability of the nanocomposites studied. The rheological and mechanical properties of the PP-hBNN nanocomposite films were also determined depending on the particle loading ratio. Optimum particle content providing the best thermal, mechanical, and rheological properties were found to be 3% wt.

On the injection molding of thick‐walled thermoplastic vulcanizates: linking static and dynamic mechanical properties with morphology

AbstractElastomers are widely used in the automotive industry in anti‐vibration components. Commonly, elastomeric anti‐vibration components are made of thermoset rubbers. However, new drivers related to the requirements of the new sustainable mobility industry are pushing towards the substitution of thermoset rubbers by thermoplastic elastomers. Among thermoplastic elastomers, thermoplastic vulcanizates (TPVs) represent an interesting material choice for anti‐vibration products due to their light weight, recyclability, ease of processing by means of injection molding and design flexibility. In this work, the correlation between static and dynamic mechanical properties and the morphology of injection molded thick‐walled TPVs is investigated. Interestingly, when comparing TPVs of different hardnesses, the softest TPV demonstrated an improvement in elastic ability to recover of up to 50% in transverse to flow direction as well as a highly anisotropic viscoelastic behavior. These phenomena are interpreted in terms of the orientation of ethylene‐propylene‐diene particles together with polypropylene crystals and chain alignment observed in microstructural characterization tests. This study opens new opportunities to develop TPV‐based anti‐vibration components with superior elasticity and customizable static and dynamic mechanical properties by considering the anisotropic character of soft TPV materials in product design and development strategies. © 2022 Society of Industrial Chemistry.

Hyperbranched polyamide-amine based phosphorous-containing flame retardant for simultaneous flame retardancy and high performance of polypropylene

Currently, the promotion of flame retardancy is facing apparent decrease of mechanical properties for polyolefin, leading to an unresolved contradiction in this field. In this work, novel hyperbranched polyamide-amine based phosphorous-containing flame retardant PPAM-AT was designed to fabricate flame-retarded polypropylene (PP). Interestedly, when the flame retardancy of PP was greatly improved after incorporation of PPAM-AT, mechanical properties of flame-retarded PP were barely damaged compared with corresponding properties of neat PP. At 15% PPAM-AT, the limiting oxygen index (LOI) of PP/PPAM-AT15 reached 30% and the highest V-0 grade was achieved in the burning test; the peak of heat release rate (PHRR) and fire growth rate of PP/PPAM-AT15 were decreased by 83.8% and 60.7% in comparison with corresponding values of neat PP. Meanwhile, tensile strength and elongation at break for PP/PPAM-AT15 maintained at 46.9 MPa and 551.3%, respectively, keeping at a comparative level with that of PP. Analysis on flame-retardant mechanism confirmed that typical intumescent flame retardation played a vital role for the excellent fire safety of PP/PPAM-AT. The reason for excellent mechanical properties of flame-retarded PP/PPAM-AT is ascribed to the multiple factors such as the change in the crystallization of PP, excellent energy-dissipating ability of PPAM-AT, and so on. This work demonstrated that hyperbranched polyamide-amine based phosphorous-containing flame retardant with unique chemical structure may achieve simultaneous flame retardancy and high performance of polypropylene, which opens a new pathway to solve the contradiction between flame retardancy and high performance of polyolefin.

The effect of process parameters on the properties of elastic melt blown nonwovens: Air pressure and DCD

AbstractAn elastic masterbatch and elastic melt blown nonwovens are prepared based successively on styrene‐ethylene/butylene‐styrene (SEBS) and polypropylene (PP) blend. The phase separation morphology, rheological properties and crystal structure of the elastic masterbatch are investigated. The results show that a compatible and stable structure is obtained in molten SEBS and PP blend with excellent mobility in the temperature range of 210–230°C. The crystallization of PP slows down resulting in a finer structure due to the restriction of the SEBS network structure with rarely change of crystalline structure. The relationship between process parameters and properties of the elastic nonwoven is also studied in detail. Air pressure and die to collector distance (DCD) have discernible effects on fiber diameter and bonding between fibers, further influencing the performances of nonwovens including porosity, tensile strength and elastic recovery. Elastic recovery is shown to be significantly more affected by DCD than by air pressure.