Neat PP Research Articles

Reciprocating sliding wear behavior of talc-filled polypropylene: Effect of talc proportion

This study investigates the tribological behavior of talc-filled polypropylene (PP-talc) via reciprocating sliding tests. These tests are realized in dry conditions and at room temperature. The cyclic sliding tests were realized using a spherical steel slider with a speed of 30 mm/s under the normal load of 10 N and along a distance of 15 mm. The maximal number of cycles was 15000. Four proportions of talc were utilized: 0 % (neat PP), 5 %, 10 %, and 50 %. Both friction coefficient (COF) and wear rate (Wr) were determined and discussed as a function of talc proportions and the number of sliding cycles. Furthermore, these findings were discussed regarding the induced damage patterns examined via Scanning Electronic Microscopy (SEM). The findings show that the low talc proportion, less than 10 %, leads to lower and stabilized COF with nearly the same value and also to a lower wear rate, Wr, relative to the high talc proportion. The COF evolution during the friction was generally occasioned by the stick-slip phenomenon, which is accentuated by the talc proportion. Nevertheless, noticeable high values of these tribological parameters were obtained when using a high talc proportion of 50 %. The SEM analyses of the worn surface after 15000 cycles revealed different damage forms: material displacement, chip formation, rolls, and delamination wear. The formation and displacement of chips within the groove are accentuated by increasing the talc proportion.

Melt compounding of spray-dried cellulose nanofibrils/polypropylene and their application in 3D printing

Micro- and nano-scale cellulosic fillers exhibit excellent dispersion and distribution within a thermoplastic matrix during the process of melt compounding or injection molding. In this study, spray-dried cellulose nanofiber (SDCNF) powders were manufactured using a pilot-scale rotating disk atomizer spray dryer. Bleached Kraft pulp (BKP), unbleached Kraft pulp (UKP), and old corrugated cardboard pulp (OCC) fibrillated at a fines level of 90% were used as feedstock materials for spray-drying. BKP-, UKP-, and OCC- SDCNFs were compounded with polypropylene using a twin screw co-rotating extruder. Maleic anhydride grafted polypropylene (MAPP) was used as a coupling agent in the composite formulations. The tensile, flexural, and impact properties of SDCNF-filled PP composites increased at 10 wt% SDCNF loading. The presence of SDCNFs in the PP matrix resulted in faster crystallization and a 12% reduction in the degree of crystallinity of the neat PP. The coefficient of thermal expansion (CTE) of neat PP was reduced by up to 31% attributable to the presence of the SDCNFs. Application of the SDCNF-reinforced PP composites in 3D printing reduced the shrinkage rate of the printed neat PP by 39%, and the printability of the PP was significantly improved with the addition of the SDCNFs.

Basalt fiber reinforced polypropylene to manufacture 3D printed composites

AbstractPolypropylene (PP) is one of the most used polymeric materials worldwide, either as a neat material or as a matrix for composite manufacture employing a molding process. Fused deposition modeling (FDM) 3D printing is an alternative process that offers the potential for manufacturing value‐added products from PP. However, using neat PP for FDM is challenging because 3D‐printed PP warps and shrinks when cooled, and the mechanical properties of PP are poor. PP‐based composites with different fillers (e.g., glass, carbon, and natural fibers) have shown improved properties using FDM processes. An alternative filler for 3D‐printed PP‐based composites is basalt fiber (BF). The objective of this work was to assess the potential and impacts of BF as a filler for BF‐PP composites using FDM processes. PP was compounded with 15, 25, 35, and 45 wt% BF to produce filaments for 3D printing without adding any compatibilizer. Results of rheology studies, morphology, and mechanical and thermal properties of the 3D printed specimens showed that BF positively impacts Young's modulus (E), thermal stability, and dimensional stability of the composite. All composites, when processed at high shear rates (i.e., above 100 1/s), show approximately similar rheological behavior. E is almost doubled in the composite with 25 wt% BF and increased fourfold in the composite with 35 and 45 wt% BF, compared to neat PP. The Izod impact resistance of the formulations containing 35 and 45 wt% BF is ~70% that of neat PP. BF process easily and adequately reinforces PP composites manufactured via FDM.Highlights Neat PP's poor mechanical properties are improved by adding basalt fiber (BF). Up to 45 wt% BF was used to reinforce PP‐based composites. PP‐BF composites are easier to process via DFM compared to neat PP. BF improves PP‐based composite's thermal and dimensional stability.

Functionalized boron nitride nanosheets and their polypropylene nanocomposites: influence on thermal, mechanical, rheological and wear behaviour

ABSTRACT The few-layer hexagonal boron nitride (hBN) nanosheets with hydroxyl (−OH) functional group at edges are synthesized using heat treatment of micron size hBN powder followed by sonication. These nanosheets are modified with a silane coupling agent, 3-Aminopropyl,triethoxysilane (APTES). The synthesized hBN nanosheets are mixed with the PP matrix using twin-screw extrusion followed by injection moulding. In case of APTES-modified hBN nanosheets incorporation in the PP matrix with PP-grafted maleic anhydride (PP-g-MA) shows the formation of an imide bond between the MA functional group of PP-g-MA and the amine group of APTES modified hBN nanosheets revealing compatibilization. The flow behaviour index values are lower for hBN nanosheets filled PP nanocomposites showing the improved processability from Rheological characterization. The few-layered – OH and APTES modified hBN nanosheet incorporation in the PP matrix improves the tensile and thermal properties. The incorporation of APTES modified hBN nanosheet in the PP matrix shows an increase in tensile modulus (18.1%) and tensile strength (8.1%) respectively. Wear studies show the incorporation of – OH and APTES modified hBN nanosheets in the PP matrix decreases the coefficient of friction and wear rate significantly. The wear rate at 4 min of wear testing for modified hBN nanosheet in the PP nanocomposites is ~ 96% less in comparison with neat PP. The wear mechanism is established from wear measurements and scanning electron microscopy (SEM) of worn-out wear surfaces of PP nanocomposites.

Enhancing energy storage property of polypropylene‐based sandwich composites with surface‐modified nonzero dimensional nanomaterials

AbstractPolypropylene (PP) is a classical organic material for dielectric capacitor, exhibiting typical linear charge–discharge characteristics. However, its low energy density fails to meet the operating requirements of high‐power and energy storage systems. In this study, techniques such as spray‐coating, lamination hot‐pressing, melt blending, and in situ melt‐drawing are employed to fabricate PP‐based sandwich‐structured composite dielectrics. The outer layers consist of BN nanosheets (BNNSs)/PP composite, while the middle layer comprises Ba0.7Sr0.3TiO3@Polydopamine (BST@PDA)/PP. The introduction of BNNSs with a wide bandgap improves the breakdown strength of composites. BST@PDA increases the overall polarization of the composites and alleviates the local electric field concentration caused by hetero‐interfacial field distortion. When the filling concentration of BNNSs is 0.10 wt% and that of BST@PDA nanowires is 3 wt%, the composite demonstrates a high dielectric constant and low dielectric loss. Additionally, the sandwich‐structured composite, exhibiting a high charge–discharge efficiency of 97.80%, presents enhanced breakdown strength (Eb ~ 453 MV/m) and increased energy storage density (Ue ~ 5.67 J/cm3), which are 39.38% and 189.29% higher than neat PP (325 MV/m, 1.96 J/cm3), respectively. This study offers a viable and efficient approach to augment the energy storage density of PP‐based dielectrics.

Effect of processing conditions on morphology and mechanical damage in glass‐reinforced polypropylene composite

AbstractThis study aims to analyze the effect of processing parameters, particularly the cooling rate, on the morphology and mechanical properties of reinforced glass fiber polypropylene (GF‐PP) films. To achieve the objective, a multi‐scale analysis was performed to study the different morphology of neat PP and reinforced PP films obtained by controlling the thermal condition during the fabrication process. Films of PP with a thickness of about 100 μm have been prepared to observe the crystalline microstructure's formation and follow its kinetics on the scale of the spherulites. The same procedure was followed using a single glass fiber to obtain the mono‐composite film of PP by controlling the interface/interphase between the fiber and the matrix. Moreover, the dependence of the damage mechanisms on the spherulite diameters and the mechanical test conditions was established. The deformation mechanisms (intra and inter‐spherulitic damage) were analyzed qualitatively and quantitatively according to the controlled morphologies produced for the polymer and the composite, especially at the level of the transcrystalline phase. The results confirm that the processing parameters affect not only the width of the transcrystalline phase but also the morphology of the fiber‐matrix interface. Furthermore, increasing the thickness of the transcrystalline phase exhibited remarkably higher interfacial shear strength, as demonstrated by the single fiber fragmentation test.Highlights Impact of cooling rate on morphology and mechanical properties of glass fiber polypropylene (GF‐PP). Multi‐scale analysis to investigate the distinct morphologies of PP and GF‐PP. Deformation mechanism particularly intra and inter‐spherulitic damage. Attention to the impact on the transcrystalline phase and the fiber‐matrix interface. Influence of transcrystalline phase thickness on interfacial strength.

Synthesis of PMM and Synergistic Flame Retardant Effect with Ammonium polyphosphate

A novel flame retardant poly {[(2-Methyl-acrylic acid 2-(dimethoxyphosphoryloxy)-ethyl ester]-co-[2-Methyl-acrylic acid 2-(trimethoxysiloxy)-ethyl ester]} (PMM) containing dimethoxyphosphoryloxy and trimethoxysiloxy groups in side chains was synthesized. The structure of PMM was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H NMR), and the thermal performance of PMM was characterized by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect of PMM on polypropylene’s flame retardancy and thermal behaviors was investigated by limited oxygen index (LOI), vertical burning test (UL-94), and TG tests. The experimental results indicate that the addition of PMM helps to improve the flame retardancy and thermal stability of PP. When the addition of PMM and APP in PC was 15% and 20%, the LOI value of PC reached 28.4%, and the UL-94 test rating reached V-0 level. The charred structure observed by scanning electron microscopy (SEM) indicated that the char surface for PP/APP/PMM system holds an intumescent char structure compared to neat PP, and the synergy exists in the composites. The PMM slightly decreased the tensile property in terms of strength but increased the elongation at break for PP composites.

Improvement of Water Vapor Permeability in Polypropylene Composite Films by the Synergy of Carbon Nanotubes and β-Nucleating Agents.

A notable application of polymeric nanocomposites is the design of water vapor permeable (WVP) membranes. "Breathable" membranes can be created by the incorporation of micro/nanofillers, such as CaCO3, that interrupt the continuity of the polymeric phase and when subjected to additional uniaxial or biaxial stretching this process leads to the formation of micro/nanoporous structures. Among the candidate nanofillers, carbon nanotubes (CNTs) have demonstrated excellent intrinsic WVP properties. In this study, chemically modified MWCNTs with oligo olefin-type groups (MWCNT-g-PP) are incorporated by melt processes into a PP matrix; a β-nucleating agent (β-ΝA) is also added. The crystallization behavior of the nanocomposite films is evaluated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The WVP performance of the films is assessed via the "wet" cup method. The nanohybrid systems, incorporating both MWCNT-g-PP and β-NA, exhibit enhanced WVP compared to films containing only MWCNT-g-PP or β-NA. This improvement can be attributed to the significant increase in the growth of α-type crystals taking place at the edges of the CNTs. This increased crystal growth exerts a form of stress on the metastable β-phase, thereby expanding the initial microporosity. In parallel, the coexistence of the inherently water vapor-permeable CNTs, further enhances the water vapor permeability reaching a specific water vapor transmission rate (Sp.WVTR) of 5500 μm.g/m2.day in the hybrid composite compared to 1000 μm.g/m2.day in neat PP. Notably, the functionalized MWCNT-g-PP used as nanofiller in the preparation of the "breathable" PP films demonstrated no noteworthy cytotoxicity levels within the low concentration range used, an important factor in terms of sustainability.

Compatibilizing effect of grafted recycled graphene on the viscoelasticity and mechanical performance of polypropylene composites

The interface problem encountered with the graphene addition in polyolefin composites is an important issue and it is necessary to use various compatibilizers to overcome this problem. Maleic anhydride grafted Polypropylene (MAPP), which is an extensively used compatibilizer in PP composites tends to eliminate these interfacial problems by interacting physically through PP chains and allows easier stress transmission from matrix to reinforcer. However, there is a lack of understanding about how this compatibilizer works with graphene-based PP composite systems since MAPP is mostly used to harmonize hydrophilic surfaces of fillers with non-polar PP. With this study, instead of direct usage of MAPP and GNP separately, waste tyre driven graphene nanoplatelets (GNP) was grafted by MAPP and the resulted material (MAPP-g-GNP) was compounded with PP by applying high shear rates at a melt phase. Effect of MAPP-g-GNP on the processability, viscoelastic response, and mechanical performance of PP composites were investigated, and high degree of interfacial enhancement was achieved by chemically combined MAPP with amphiphilic type of GNP in PP matrix. The use of MAPP-g-GNP at a loading ratio of 0.1 wt% resulted in 38% increase in flexural modulus and 26% in flexural strength and tensile modulus compared to neat PP. The two additives used in the PP composite (2 wt% MAPP and 0.1 wt % GNP) were reduced to a single additive (PP/MAPP-g-GNP) with a 95% weight reduction in the additive content of PP. Rheological studies support that MAPP is not as successful as MAPP-g-GNP in strengthening the interface when used alone with GNP due to the lower complex viscosity and the higher crossover frequency. This study contributes to the production of high-performance PP materials with a very low amount of combined GNP and compatibilizer by integrating the circularity approach in compound development by using GNP obtained from recycled and upcycled waste tyres.

Fabrication of highly hydrophobic layered double hydroxide decorated with tannic acid cross-linked phosphazene as a novel flame retardant for polypropylene

Layered double hydroxide (LDH) is a promising flame-retardant nano-additive for polymers, however, its efficiency is highly based on its composition and dispersity. Based on this cognition, a core-shell LDH-based architecture (LDH@TA-HP) was designed using LDH sheet as core and tannic acid and phosphazene cross-linkd polymers network (TA-HP) as shell. In the flame retardant process, renewable tannic acid (TA) as a carbon source with phosphazene was combined to form an intumescent flame-retardant system, which synergizes with the “tortuous path” effect of LDH which greatly enhance the flame retardancy of PP and LDH@TA-HP composites (PP/LDH@TA-HP). With the addition of 20 wt% LDH@TA-HP, the peak heat release rate and total smoke production of the PP/LDH@TA-HP composites were decreased by 63.5% and 47.6%, respectively, in comparison with those of Neat PP. The flame retardant level reached UL-94 V-0 rating and the limiting oxygen index (LOI) value of PP/LDH@TA-HP composites reached 30.1%, which was related to the “tortuous path’’ effect of LDH and the formation of the intumescent char layer of TA-HP. This investigation provided a facile strategy for the design of multifunctional LDH-based hybrids, expanding LDH potential applications in polymer composites.

Nanocellulose reinforced lightweight composites produced from cotton waste via integrated nanofibrillation and compounding

Cotton is a natural fiber containing more than 95% of cellulose. With worldwide cotton consumption continuously increasing, the amount of cotton waste generated is enormous. Most of the cotton waste ends up in landfill or incinerators, resulting in a huge waste of this excellent natural resource. In this project, cotton waste was recycled to produce polypropylene nanocomposites. Instead of using the traditional two-step nanofiber extraction and compounding technique, an integrated process was adopted to combine nanofibrillation and compounding into one step. Results showed that cotton fibers with a slight prefibrillation and hydrophobic surface modification were successfully fibrillated into tens to hundreds of nanometers in width during compounding. The nanofibers reinforced polypropylene composites exhibited significantly enhanced tensile and flexural strength and moduli. For instance, when 30% fibers from bleached white and indigo-dyed denim fabrics were introduced, the tensile moduli of the resultant composites reached 4.57 and 4.59 GPa, respectively, compared to 1.60 GPa, the modulus of neat PP. Meanwhile, denim fabrics had a remarkable reinforcing effect on the composites’ impact strength attributing to the hydrophobic indigo dyes that improved the interfacial bonding between cotton fibers and the matrix. The highest impact strength of denim reinforced composites was 4.96 kJ/m2 with 20% fiber loading; while the impact strength of neat polypropylene was 2.46 kJ/m2. The low water uptake of the composites further indicated the excellent adhesion at the filler/matrix interface. In general, a very promising processing technique to recycle cotton waste for high-value products was demonstrated.

Autoclave foaming and steam-chest molding of polypropylene/polybutene-1 blend bead foams and their crystallization and mechanical properties

Expanded polypropylene (EPP) foams have showed wide applications in our daily life, such as automotive and packaging. Usually, autoclave foaming combined with steam-chest molding is the main artwork to prepare the high-precision EPP foam products. However, the foaming behavior of EPP and the excessive pressure required for molding still need to be further improved, which is great significance for energy saving and cost saving, etc. Herein, this study finds that adding a certain amount of polybutene-1 (PB-1) into the PP can help to reduce the temperature and pressure required for foaming/molding, and to broaden the foaming temperature. For example, in order to make the foam beads bonding well and with the expansion ratio of 20, the molding pressure should be higher than 2.7 bar for Neat PP foams, but just 1.5 bar for PP/PB-1 mixtures. Moreover, the effects of PB-1 content on the crystallization properties and foaming/molding behaviors of the PP/PB-1 bead foams are illustrated, and then the mechanical properties are also studied. Furthermore, the low-pressure foaming strategy presented here is beneficial for reducing the barriers of energy consumption and promoting the development of new bead foam materials.

How nucleating particles migration affects the fractionated crystallization of isotactic polypropylene/polystyrene immiscible blends

We investigate the inter-phase migration of nucleating particles and their effect on the fractionated crystallization of polypropylene droplets dispersed in an immiscible polystyrene matrix by preparing melt-mixed 90/10 wt% PS/PP blends with selected nucleating agents. Different concentrations of nucleating agents (NAs): Phtalocianene Blue, NA11, Talc, and sodium benzoate, were initially incorporated either in neat PP or in neat PS. Then the different PS/PP/NAs blends were prepared. Contact angles were determined for the neat polymers and the NAs, and the results indicated that, from a thermodynamics point of view, all NAs should remain or migrate to the PS phase. According to SEM observations, a sea-island morphology was obtained that did not vary with NA addition. Hence the results should be independent of differences in the morphology.PP droplets crystallized in neat blends in three well-differentiated crystallization peaks (i.e., fractionated crystallization). The NAs induce a concentration-dependent increase in the high-temperature crystallization peak at the expense of reducing the low-temperature peaks, as droplets become in contact with or contain the NAs. When compared at a constant concentration in one of the phases, the nucleating agents have efficiencies that decrease in the order: Pht Blue ≈NA11>Talc>Sod Benz. Surprisingly, for the three most effective NAs, it was found that adding them initially to the PS phase led to a much higher nucleation efficiency (evaluated in terms of increases in peak crystallization temperature) than adding them to PP. This indicates that these NAs, initially present in the PS phase, migrate to the interface or to the bulk of the PP phase (against thermodynamics). Sod Benz was the only exception, as it shows a higher thermodynamic affinity to the PS phase. We explain the migration of most particles from the PS phase to the phases’ boundary or to the bulk of the PP droplets by considering that kinetic factors dominate the behavior, as, from a rheological perspective, the minor component (PP) always displays a lower viscosity than the matrix component (PS) under the chosen mixing conditions.

Chemical, Thermal and Mechanical Characterization of Licorice Root, Willow, Holm Oak, and Palm Leaf Waste Incorporated into Maleated Polypropylene (MAPP).

The effect of four lignocellulosic waste fillers on the thermal and mechanical properties of biocomposites was investigated. Powdered licorice root, palm leaf, holm oak and willow fillers were melt compounded with polypropylene at two different weight contents, i.e., 10 and 30, and then injection molded. A commercially available maleated coupling agent was used to improve the filler/matrix interfacial adhesion at 5 wt.%. Composites were subjected to chemical (FTIR-ATR), thermal (TGA, DSC, DMA) and mechanical (tensile, bending and Charpy impact) analyses coupled with a morphological investigation by scanning electron microscopy. Although similarities among the different formulations were noted, holm oak fillers provided the best combination of thermal and mechanical performance. In particular, at 30 wt.% content with coupling agent, this composite formulation displayed remarkable increases in tensile strength and modulus, flexural strength and modulus, of 28% and 110%, 58% and 111%, compared to neat PP, respectively. The results imply that all these lignocellulosic waste fillers can be used successfully as raw materials for biocomposites, with properties comparable to those featured by other natural fillers.

Interface‐engineered polypropylene/cellulose nanofibril composites with enhanced thermal stability, mechanical modulus, and impact strength

AbstractTo attain interface‐engineered polypropylene/cellulose nanofibril (PP/CNF) composites with improved thermal and mechanical performance, PP was grafted with glycidyl methacrylate (GMA) and styrene via direct melt‐mixing and GMA/styrene‐grafted PP (PGMA) was reinforced with 1–10 wt% CNF content through a mass‐producible melt‐compounding process. The spectroscopic analyses confirmed the existence of specific hydrogen‐bonding interactions between CNF and PGMA in the composites. The melt‐rheological measurement revealed the occurrence of chemical reactions between the hydroxy group of CNF and the glycidyl group of PGMA of the composites. Accordingly, the dispersion and interfacial adhesion of CNF in the PGMA matrix was improved. β‐form PP crystals were also developed by accelerating the crystallization of PGMA and PGMA/CNF composites, unlike PP with only α‐form crystals. The storage modulus of PGMA/CNF composites was enhanced noticeably with increasing CNF content. Moreover, the impact strength of PGMA composite with 1 wt% CNF was found to be 29.2% higher than that of neat PP.

Polypropylene/CaCO<sub>3</sub> Nanocomposites Fabricated Using Masterbatch: Effect of Nano-CaCO<sub>3</sub> Loadings and Re-Processing on the Melting Properties

Polypropylene filled calcium carbonate (CaCO3) nanocomposites were fabricated by employing melt blending/compounding method using masterbatch. To investigate the efffect of reprocessing on the melting properties of PP/CaCO3 nanocomposites, the melt compounding process was conducted twice (two cycles). The effect of nano-CaCO3 loadings (i.e. 5, 10 and 15 wt%) on the melting properties of PP/CaCO3 nanocomposites were also studied. The meling properties of the nanocomposites were analyzed by using a DSC (Differential Scanning Calorimetry). Additionally, the nanocomposites samples were also analyzed by an SEM (Scanning Electron Microscopy). The SEM analysis results revealed that at higher nano-CaCO3 loading (i.e. 15 wt%), the nano-CaCO3 particles in the 2nd cycle were more well distributed/dispersed in the polypropylene matrix as compared to the 1st cycle. Whereas, the DSC test results showed that the crystallinity of the nanocomposites samples were similar to that of neat PP for the 1st cycle of melt blending process, which was about 41%. In the other hand, for the 2nd cycle, the crystallinity of the samples slightly increased wtih increasing nano-CaCO3 loadings, which were about 39.6; 43; 44% for nano-CaCO3 loadings of 0, 5, 10 wt%, respectively. Nevertheless, at the highest nano-CaCO3 loadings (i.e. 15 wt%), the crystallinity of the nanocomposites (i.e. NCC-15-II) decreased again and lower than that of neat PP, which was about 37.7%.

Polydopamine primed phosphorylated sepiolite-polypropylene nanocomposite with enhanced thermal, rheological, and flame retardant properties

Phosphorous-based fire-retardant materials are considered eco-friendly and can be reinforced in polymers or functionalized on the polymer backbone to reduce combustibility. Herein, sepiolite fiber (Spl) was first primed with polydopamine (PDA), and the amine group density was increased by Michael's addition of EDA to further graft H3PO3. The stepwise modifications and formation of the phosphorylated Spl-PDA-P and Spl-PDA-EDA-P were established by analyzing surface chemical structure, surface and internal morphology, and surface area. Further, the Spl-based fillers were reinforced in the PP matrix, and the nanocomposites were systematically characterized for thermal stability, mechanical property, flow behavior, and fire-retardant properties. The PP_Spl-PDA-EDA-P nanocomposite at 5% filler loading has a tensile and flexural strength of 36.3 MPa and 50.6 MPa, respectively. The flow property was established by determining melt flow index (MFI) of 13.3 ± 0.75 g/10 min and melt rheological properties. After phosphorylation, the Spl-based fillers have shown shear thinning behavior with increased filler loading. Finally, the prepared nanocomposites were evaluated for fire retardant properties by determining the limiting oxygen index (LOI) and UL-94 vertical burning test. The neat PP has an LOI of 17.5, and a maximum improvement was observed in the case of PP_Spl-PDA-EDA-P with an LOI of 30.2. Overall, the grafting of H3PO3 on PDA coated Spl has created a robust filler to impart fire-retardant property in combustible PP.

Rheological/crystallization behavior of PP/graphite nanosheet composites and performance of microcellular foaming plastics

The large, uneven and distorted cells in foaming products seriously weakens its mechanical properties. Herein, a promising way to prepare lightweight and strong PP/graphite nanosheet(GN) nanocomposite foaming products is reported. To improve foaming performance, the effects of GN on the crystallization behavior and rheological behavior of PP are firstly systematically studied. It is found that the addition of GN not only directly improves the melt strength and viscoelasticity, but also has the dual effects of refining grain size and accelerating crystallization process. The excellent cellular structure with the average cell diameters of several microns is fabricated using m old-opening foaming injection molding (MOFIM) process, which contributes to enhanced mechanical properties. The tensile strength and modulus of PP/GN nanocomposite foams with opening distance of 1 mm is almost 50% and 70% higher than that of the neat PP solids, respectively. The nanocomposite foam also shows superior impact strength, increased to above 75% than that of the neat PP solids.

Fused deposition modeling of polypropylene-aluminium silicate dihydrate microcomposites

Abstract Polypropylene (PP) undergoes fast crystallization and resulting in rigorous shrinkage when it is subjected to high temperature likewise of the fused deposition modeling (FDM) process. This research study focuses on the investigation of the processing parameters and factors that decrease the warpage of PP during the FDM process. Aluminium silicate dihydrate (K) microparticles of different ratios were melt blended with PP by a twin-screw extruder, and filaments of about 1.7 mm diameter were extruded in a single screw extruder. Then, the extruded filaments were used to fabricate the dumbbells structure through the FDM process. The effects of optimizing the fused deposition temperature, coating the chamber with thick papers/fabrics, and coating a printer bed with PP material were also investigated in this study. Scanning and transmission electron microscopy, differential scanning calorimetry, melt flow, and mechanical properties testing instruments are used to analyze the microparticles dispersion, crystallization, flow, and mechanical properties of resulting samples. Uniformly dispersed filler and increased printing chamber temperature result in an increase of crystallization temperature and improve the dimensional accuracy of fused deposited specimens. The fused deposited PP-K10 wt% composite showed an improvement of up to 32% in tensile modulus compared to the neat PP.

Crystallization of Isotactic Polypropylene Nanocomposites with Fibrillated Poly(tetrafluoroethylene) under Elevated Pressure.

Nanocomposites of isotactic polypropylene with 1–5 wt.% of fibrillated PTFE (PP/T) were prepared, and their crystallization during cooling under elevated pressure, in a wide pressure range, up to 300 MPa, as well as the resulting structure, were examined. The crystallization peak temperatures of PP/T, especially with 3 and 5 wt.% of PTFE, exceeded by up to 13 °C those of neat PP. Moreover, a fine-grain structure was formed in PP/T in the entire pressure range, which proved the ability of the fibrillated PTFE to nucleate crystallization of PP in the γ-form under elevated pressure. This also resulted in a higher crystallinity level developed in the γ-domain, before the temperature range of the α-domain was reached during cooling. Hence, the γ-content increased in comparison to that in neat PP, under the pressure up to 200 MPa, especially under 50–100 MPa.