Isotactic Polypropylene Composites Research Articles

Recycling effects on the bending, rheological, and structural properties of glass fiber-reinforced isotactic polypropylene composites

In the present work, a combination of virgin polypropylene and E-glass fiber was subjected to ten (10) reprocessing cycles via extrusion and compression molding techniques to mimic recycling and its impacts on the bending properties of the composites. The samples were characterized using Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), and melt flow index (MFI). The results revealed a gradual depreciation in flexural properties after each reprocessing cycle. The XRD analysis indicated a substantial reduction of peak intensities, degrees of crystallinities, and average crystallite sizes, explaining the lowered flexural properties in addition to a possible reduction in glass fiber lengths (fiber attrition). Melt-processing behavior shows a progressive increase of MFI from 7 to 19.16 g/10 min, confirming the probable damage in molecular weight and loss of complex viscosity. Chemical and structural analysis showed no alteration in the polypropylene major functional groups. It is concluded that the reductions in molecular weight and composites’ properties occurred due to chain scission from recycling effects; hence, glass fiber-reinforced polypropylene composites can be recycled only three (3) times unless it is refreshed by the addition of virgin parts to compensate for the lost property.

Fundamental studies of isotactic polypropylene composites with brown coals: Structure–properties relationship

ABSTRACT Wood–polymer composites (WPCs) are commonly used in materials technology, and there is a reasonable amount of research for new kinds of green fillers. In this study, we have obtained the isotactic polypropylene (iPP) composites filled with native and modified xylite (brown coal fraction with a relatively high amount of cellulose). The modification of xylite has been based on processing in a mine, where the humic acids are rinsed with KOH solution for further use. The composites were subjected to a wide range of structural, thermal, functional, and mechanical characteristics. The results of the undertaken research have shown that the addition of xylite filler can be successfully used in obtaining of thermoplastic composites. The properties of those composites are similar to another types of WPCs. There also observed a strong impact of xylite filler addition into formation of β-iPP form.

Effect of glass fiber loading and reprocessing cycles on the mechanical, thermal, and morphological properties of isotactic polypropylene composites

AbstractIn this study, a preliminary finding is carried out to obtain the optimum E‐glass fiber content in polypropylene (PP) plastic products using loadings of 5, 10, 20, 30, and 40 wt%. The formulation with the optimum loading of 10 wt% glass fiber was reprocessed 10 times via extrusion and compression molding techniques to simulate actual recycling and impacts on service life properties such as mechanical, toughness, chemical, thermal, composition, and morphology. In the result, mechanical properties were lost after each reprocessing without effect on the chemical properties and elemental compositions. The thermal studies showed a decrease in degradation temperatures with the onset degradation temperature (TOnset) for the one‐time reprocessed PP recorded at 336.93°C with a maximum rate of weight loss (TMax) at 427.68°C which further reduced to 259.90°C (TMax of 388.47°C) after 10 extrusion run showing one‐step decomposition patterns. This work provides that glass fiber‐reinforced plastics should not be reprocessed beyond 3 times except when refreshed with the addition of virgin PP to make up for the lost property. This will be very useful for manufacturers who want to simultaneously save costs (retain profit margin) and maintain the environment.

Toward a deep understanding of the difference between isotactic and syndiotactic polypropylene on the fire performance and degradation behavior

This work investigated the difference in flame retardancy and degradation behavior of polypropylene (PP) composites with different configurations. The piperazine pyrophosphate (PAPP) was combined with melamine polyphosphate (MPP) to construct an intumescent flame retardant system, before incorporating into the PP system by melt blending. It showed that by the introduction of equal amounts of flame retardant, isotactic polypropylene composites (iPP-IFR) can achieve better flame retardancy with a desirable UL-94 V-0 rating, whereas syndiotactic polypropylene (sPP-IFR) shows poor fire performance. Melt index tests show that sPP-IFR sample is easy to flow and prone to melt drops. Differential scanning calorimetry results show that iPP-IFR has a higher degree of crystallinity. The thermogravimetric infrared coupling results show that sPP-IFR produces more small molecule hydrocarbon gases during combustion, making the system more difficult to achieve satisfied flame retardancy. The burning properties of iPP-IFR have been proven to be somewhat better compared to that of sPP-IFR, and sPP is more difficult for flame retardant modification.

Crystallization kinetics of melt-mixed 3D hierarchical graphene/polypropylene nanocomposites at processing-relevant cooling rates

Knowledge of the solidification behaviour of isotactic polypropylene (iPP) composites with reduced graphene oxide nanoplatelets is key to open the possibility to widespread use of these high performing nanocomposites. The crystallization behaviour of these systems, with filler content in the range of 0.2–3.5 wt% has been investigated by differential scanning calorimetry (up to 100 °C/min) and ex-situ structural and morphological characterization of samples prepared at processing-relevant cooling conditions (up to 2000 °C/s). Compared to the self-nucleated neat iPP, the nucleation efficiency was estimated to vary from 44 to 93% when increasing the filler content. Such a high nucleating efficiency has not been reported yet for a nanocomposite with iPP matrix. This result is due to the very good dispersion of the filler in these melt-mixed graphene-based polypropylene systems. The nucleation ability of the graphene filler does not reach a saturation in the concentration range studied. The gap between laboratory and industrial cooling rate scale is here reduced thanks to the information achieved from the fast-cooling experiments. By varying the filler amount in the investigated range, a significant shift of the cooling rate window in which the transition from α-to mesophase dominated crystallization takes place was detected. Notably, with 3.5 wt% graphene platelets, α-phase crystals are predominantly present in the material even after quenching at 1000 °C/s, similar to highly nucleated commercial iPP grades.

The Accelerated Aging Impact on Mechanical and Thermal Properties of Polypropylene Composites with Sedimentary Rock Opoka-Hybrid Natural Filler.

This paper presents the impact of accelerated aging on selected mechanical and thermal properties of isotactic polypropylene (iPP) composites filled with sedimentary hybrid natural filler-Opoka rock. The filler was used in two forms: an industrial raw material originating as a subsieve fraction natural material, and a rock calcinated at 1000 °C for production of phosphorous sorbents. Fillers were incorporated with constant amount of 5 wt % of the resulting composite, and the material was subjected to accelerated weathering tests with different exposition times. The neat polypropylene and composites with calcium carbonate as a reference filler material were used for comparison. The aim of the research was to determine the possibility of using the Opoka rock as a new hybrid filler for polypropylene, which could be an alternative to the widely used calcium carbonate and silica. The thermal, mechanical, and structural properties were evaluated by means of differential scanning calorimetry (DSC), tensile tests, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR/ATR) prior to and after accelerated aging. As a result, it was found that the composites of polypropylene with Opoka were characterized by similar or higher functional properties and higher resistance to photodegradation compared to composites with conventional calcium carbonate. The results of measurements of mechanical properties, structural and surface changes, and the carbonyl index as a function of accelerated aging proved that Opoka was an effective ultraviolet (UV) stabilizer, significantly exceeding the reference calcium carbonate in this respect. The new hybrid filler of natural origin in the form of Opoka can therefore be used not only as a typical powder filler, but above all as a UV blocker/stabilizer, thus extending the life of polypropylene composites, especially for outdoor applications.

Mechanical and Thermal Degradation Properties of Isotactic Polypropylene Composites with Cloisite15A and Cloisite20A

In this work, the influence of maleic anhydride grafted polypropylene (PP-g-MA) content on thermal and me-chanical properties of polypropylene (PP) composites with two types of clays, differing modifier density in the interlayer space, Cloisite15A and Cloisite20A, was studied. PP/clay composites were melt blended in presence of different content of PP-g-MA from 3, 6, 9, and 12 wt.%. It was found that Cloisite15A with a high density of the modifier promotes the formation of intercalated structures, while Cloisite20A with a low density of the modifier, predominantly exfoliated nanocomposites are formed. In the first case, the structure tends to become intercalated whilst composites with Cloisite20A favor the formation of predominantly exfo-liated structures. The formation of the nanocomposite is accompanied by a significant increase in thermal sta-bility (50 % weight loss is observed at temperatures of 360 °C and 430 °C for polypropylene and nanocomposites based on it, respectively). An analysis of the mechanical properties of nanocomposites gen-erally indicates an increase in the elastic modulus by 15–20 %, and this effect is more pronounced for exfoli-ated structures, the yield strength practically does not change and the elongation at break decreases noticeably.

In situ polymerisation of stereospecific propylene nanocomposites blends. Optimising mechanical properties

Isotactic (iPP) and syndiotactic (sPP) polypropylene composites and their blends containing different amounts of nanosepiolite as cocatalyst support were prepared via in-situ polymerisation using different metallocene catalysts to find out improvements in the mechanical properties in comparison with traditional PP nanocomposites obtained by melt.The results showed that the amount of nanoclay significantly affects the catalytic activity of the Cs-symmetry catalyst, obtaining nanocomposites with important microstructural changes: increased molecular weight and syndiotactic sections, narrower molecular weight distributions and increased crystallinity. The particular ordering of the crystalline sections of the sPP observed in the WAXS patterns was the main reason for the dramatic changes in the thermal and mechanical properties of the obtained nanocomposites. Although the nanocomposites obtained with catalyst mixtures maintained certain thermal properties of the iPP, these did not translate into improved mechanical properties due to the loss of crystallinity and the preference for the synthesis of syndiotactic configurations.

The inhibiting effect of basalt powder on crystallization behavior and the structure-property relationship of α-nucleated polypropylene composites

Basalt powder (BP) is a promising eco-friendly filler for polymeric composites. Due to its chemical composition, it can alter the effectiveness of various modifying agents used in the polymer industry. In this study, the influence of simultaneous addition of 5 wt% of basalt powder and 0.5 or 1 wt% of a sorbitol-based nucleating agent (NA) on the structure and properties of isotactic polypropylene (iPP) composites was analyzed. The potential chemical reactions of BP and NA were evaluated by Fourier transform infrared spectroscopy. The influence of the additives on the crystallization of the polymer was studied by differential scanning calorimetry, optical microscopy in polarized light, and rheological measurements. The kinetics of crystallization was analyzed using Mo and Friedman methods. The structure of the composites was observed by scanning electron microscopy. The mechanical properties were also evaluated. It was found that the BP reacts with the NA, which limits its ability to form the microfibrillated network in the melt. As a result, the crystallization behavior of the nucleated basalt-filled iPP is almost the same as in the case of the composite without the NA. However, the samples containing both NA and BP present good mechanical properties and adhesion between the polymer and the filler.

Quasi-static and low-velocity impact responses of polypropylene random copolymer composites with adjustable crystalline structures

Currently, the effect of cooling rates on mechanical properties of continuous glass fiber-reinforced isotactic polypropylene (CGF/iPP) composites cannot be well revealed, due to the imperfect impregnation containing voids, limited selection of crystalline structures (i.e., boundary defects and lamellae thickness) and impact energy. Moreover, compared to the polypropylene random copolymer (PPR) with toughness-rigidity balance, the brittleness of iPP and incompatibility of iPP/elastomer system also limit the further improvement of impact resistance. Furthermore, to date, the influence of cooling rates on mechanical properties of CGF/PPR composites has not been reported. Herein, we reveal the influence mechanism of multiple crystalline structures on quasi-static, and on low-velocity impact behavior of CGF/PPR composites based on perfect impregnation. Results show that the tensile strength and impact resistance under perforation threshold both increase first and then decrease with the increased cooling rate, while the impact resistance at non-perforation threshold gradually improves. Severe boundary defects mask the contribution of other crystalline structures, resulting in the lowest tensile strength. After overcoming boundary defects, the type of lamella is the most important factor for the effect of stress transfer. In the case of non-perforation damage, laminate with the smallest crystallinity and the widest size distribution only suffers from subcritical damage. The stiffness of amorphous area generated by the density of tie chains and chain entanglements becomes the decisive factor for improving impact resistance of laminate above perforation threshold. This work may pave the way for improving mechanical properties of thermoplastic composites via generating specific crystalline structures.

Spatial structure and aggregation of carbon allotrope nanofillers in isotactic polypropylene composites studied by small-angle neutron scattering

We study the aggregation of carbon allotrope nanofillers in the matrix of isotactic polypropylene with direct small-angle neutron scattering measurements. With the ATSAS software, we analyzed the data and determined the fractal shape, dimension, and sizes of nanofiller aggregation in the bulk of isotactic polypropylene over the range of the scattering angles. We estimated the volume distributions and aggregation of different types of carbon nanofillers at different concentrations: nanographite, graphene nanoplatelets (GNP), fullerenes, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT) and binary fillers MWCNT/GNP. We reconstructed the shape of nanoscale particles and aggregates of a few nanofillers SWCNT, MWCNT and MWCNT/GNP and found that the systems are polydisperse; nanofillers associate in the volume of isotactic polypropylene as fractal dense aggregates with rugged surface, their sizes exceeding original dimensions of nanofillers several times.

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.

Rheological and single screw extrusion processability studies of isotactic polypropylene composites filled with basalt powder

The development of novel composite materials with beneficial mechanical, thermal and electrical properties often focus only on the final properties of the products. However, in many cases their significant application potential may be suppressed by limitations resulting from their rheological and processing properties. The isotactic polypropylene (iPP) composites filled with basalt powder (BP) are known for their good thermomechanical stability and stiffness. The paper presents the complex results of off-line rheological measurements (oscillatory, capillary and torque rheometry) related to processing behavior obtained in a laboratory conditions with the use of a processing machine (single screw extruder), which allow understanding the different manner of the processing behavior occurring during the melt processing of iPP-BP composites. It was found that the addition of BP may cause unusual, beneficial effect of lowered viscosity of the melt. While the addition of up to 5 wt% of BP results in a profitable reduction of the pressure in the barrel during extrusion without influence on the throughput, a higher amount of the filler may lead to significant processing limitations due to strong wall slip.

High impact strength of polypropylene composites with complex titanate whiskers/multiwalled carbon nanotubes

Isotactic polypropylene (PP) composites achieved high impact strength by melt mixing with complex titanate whiskers/multiwalled carbon nanotubes (MWCNTs). The complex fillers, obtained via coupling agent γ-aminopropyl triethoxysilane, triggered additional reinforcement with stiff backup of whiskers and strengthened interfacial adhesion generated from MWCNTs, forwarding positive synergy on the PP composites. In presence of compatibilizer maleic anhydride-grafted polypropylene, 5 wt% of the complex fillers brought about impact strength 6.3 ± 0.3 kJ/m2 to the composite, which was 103% higher than PP. Meanwhile, tensile strength was also improved with 34.8 ± 0.5 MPa as compared with that of PP (32.6 ± 0.3 MPa). Morphology witnessed by scanning electron microscope revealed that the complex fillers favored dispersion of MWCNTs in polymer matrix, fulfilling bridging for reinforcement. Detection of differential scanning calorimetry also indicated that the complex fillers facilitated crystallization of PP in the composites. Upon high impact strength and improved tensile property, the PP composites could find potentials with facile processing manipulation in applications.

Effect of small amount of multi-walled carbon nanotubes on crystallization and thermal-mechanical properties of overflow microinjection molded isotactic polypropylene

Herein, the solution-melt blended multi-walled carbon nanotubes (MWCNTs)/isotactic polypropylene composites are molded by an overflow microinjection molding. All parts exhibit the highly oriented structures, and the number of oriented shish-kebab structures progressively increase with increasing MWCNTs content. More importantly, small amount of MWCNTs (i.e., 0.1 wt%) can significantly improves crystallization rate and crystallinity of all composite parts, nevertheless, the formation of β-crystal is remarkably suppressed. Moreover, compared with the pure part, tensile modulus, toughness and thermostability of composite parts are mildly enhanced. This work provides a facile method to fabricate high-performance composite parts via overflow microinjection molding, which would lay a foundation for optimizing the macroscopic performances of polymer-based composites.

Structure and properties of fiber-reinforced polypropylene prepared by direct incorporation of aqueous solution of poly(vinyl alcohol)

Poly (vinyl alcohol) (PVA) is immiscible with most conventional plastics and also unsuitable for melt processing owing to its extensive hydrogen bonding. Therefore, there have been few studies concerning the melt-mixing of PVA with standard plastics. The present paper describes a novel technique for producing isotactic polypropylene (PP) composites containing PVA fibers by directly introducing an aqueous solution of PVA into molten PP from an injection nozzle in a twin-screw extruder having a wide venting port. The PVA fibers were found to be dispersed homogeneously in the composites obtained by this method. Furthermore, an injection-molded product made from this composite exhibited an increased modulus, high yield strength, and high heat distortion temperature. These properties are attributed to the significant degree of orientation of both the PP chains and the PVA fibers. The nucleating action of the PVA fibers oriented in the flow direction is responsible for the structure of the composite, which in turn results in attractive properties.

Structure and Mechanical Properties of Multi-Walled Carbon Nanotubes-Filled Isotactic Polypropylene Composites Treated by Pressurization at Different Rates.

Isotactic polypropylene filled with 1 wt.% multi-walled carbon nanotubes (iPP/MWCNTs) were prepared, and their crystallization behavior induced by pressurizing to 2.0 GPa with adjustable rates from 2.5 to 1.3 × 104 MPa/s was studied. The obtained samples were characterized by combining wide angle X-ray diffraction, small angle X-ray scattering, differential scanning calorimetry, transmission electron microscopy and atomic force microscopy techniques. It was found that pressurization is a simple way to prepare iPP/MWCNTs composites in mesophase, γ-phase, or their blends. Two threshold pressurization rates marked as R1 and R2 were identified, while R1 corresponds to the onset of mesomorphic iPP formation. When the pressurization rate is lower than R1 only γ-phase generates, with its increasing mesophase begins to generate and coexist with γ-phase, and if it exceeds R2 only mesophase can generate. When iPP/MWCNTs crystallized in γ-phase, compared with the neat iPP, the existence of MWCNTs can promote the nucleation of γ-phase, leading to the formation of γ-crystal with thicker lamellae. If iPP/MWCNTs solidified in mesophase, MWCNTs can decrease the growth rate of the nodular structure, leading to the formation of mesophase with smaller nodular domains (about 9.4 nm). Mechanical tests reveal that, γ-iPP/MWCNTs composites prepared by slow pressurization display high Young’s modulus, high yield strength and high elongation at break, and meso-iPP/MWCNTs samples have excellent deformability because of the existence of nodular morphology. In this sense, the pressurization method is proved to be an efficient approach to regulate the crystalline structure and the properties of iPP/MWCNTs composites.

Creep behavior and mechanical properties of isotactic polypropylene composites via twice melt injection molding

Abstract Nowadays, the improvement of injection molding technology development research is in great demand due to the limitation of convenient injection molding for structural engineering applications. For injection-molded products, oriented structure is ubiquitous. To promote the formation of oriented structure, exert a positive impact on the final mechanical properties of polymer products, an advanced injection molding process is used to achieve multiple shear melt in this work. Based on our previous work about melt multi-injection molding technology, to investigate the influence about oriented structure of composites attracted by higher shear stress, iPP/MWCNTs and iPP/β-NA composites were studied. Compared to traditional injection-molded samples, the addition of MWCNTs impede the formation of oriented structure. For iPP/β-NA composites, the higher flow shear stress inside the mold wall increase the overall crystallinity but restrain the growth of β-crystal.

β-modification of isotactic polypropylene induced by electrospun isotactic polystyrene fibers

Isotactic polypropylene (iPP) composites filled with electrospun isotactic polystyrene (iPS) fibers were prepared through solution blending by sonication in a nonsolvent water bath. After optimal sonication treatments, the entangled and surface-fused iPS fibers in the nonwoven fabrics were disentangled and separated to facilitate better dispersion in the as-prepared composites. Composites with different fiber concentrations (0.01, 0.1, and 1 wt%) subjected to various thermal treatments were characterized using DSC, POM, and simultaneous WAXD/SAXS. The effects of cooling rates and crystallization temperatures on the formation of β -form crystals and lamellar morphology were extensively studied. Results showed that electrospun iPS fibers are novel β-nucleating agent towards iPP to enhance crystallization rate. A β-form content of ∼50% was achieved at a fiber concentration of 0.1 wt%, and the β-form content increased with increasing cooling rate. Under isothermal crystallization, the maximum β-form content was found at 120 °C, lying between the Tαβ and Tβα; the former is associated with α-to-β and the latter is relevant to the β-to-α crystal transformation due to the difference in the growth rates of both α and β phases. This finding is consistent with POM observations, revealing that a transcrystalline layer of dense α-form nuclei is first induced at the iPS fiber surface for initial crystal growth, followed by α-to-β bifurcation growth to develop highly birefringent β-form crystals. The average lamellar thickness derived from SAXS results is dependent on the supercooling degree, as well as on the relative content of α/β crystals developed in the composites.

The Investigations of Thermomechanical Properties of Polypropylene Composites

The article presents the results of the investigations of isotactic polypropylene composites with the following fillers: flame retardants, glass fiber, glass beads, and talc. The process of preparing composites and test samples is described. The investigations were performed using the DMTA method. The evaluation of thermal effects for the investigated molded parts using special device was also presented. The scope of the research included ten polypropylene composites with different content and type of fillers. These measurements allowed us to determine the influence of the filler type and content on the dynamic mechanical properties of iPP composites. The results will be useful for determining the scope of application of the mentioned materials in various fields of industry in the future.