Polypropylene Parts Research Articles

Mechanical Decrosslinking and Reprocessing of Crosslinked Rotomolded Polypropylene Using Cryogenic-Assisted Shear Pulverization and Compression Molding

This paper presents a novel recycling approach for porous/foamed crosslinked rotomolded polypropylene (xPP) parts, originally designed for lightweight and thermal insulation. The method uses a cryogenic-assisted shear pulverization technique to produce parts by compression molding. The part’s final gel content and crosslink density were found to depend on their dicumyl peroxide (DCP) content (0–2.5 phr) and characterized in terms of their chemical, thermal, physical and mechanical properties. The results show that this recycling technique allows for an effective reprocessing of the crosslinked materials since partial decrosslinking occurs. For example, the crosslink density decreased by 64% (3.10 to 1.11 × 10−3 mol/cm3) and the gel content by 9% (84.4% to 71.2%) at 2.5 phr DCP. Reprocessing through compression molding led to a compact and partially crosslinked structure resulting in significant improvements in terms of tensile strength (1480%), tensile modulus (604%), elongation at break (8900%), Shore A hardness (19%) and Shore D hardness (32%) compared to xPP samples (at 2.5 phr). This study paves the way for the development of more sustainable recycling methods, especially for crosslinked polymers, by providing new opportunities to reuse the wastes/end-of-life materials in advanced materials and different applications.

Advancing laser transmission welding for additive manufacturing: A study of glass fiber reinforced polypropylene parts

Laser transmission welding (LTW) is a well-established technique for joining high-volume thermoplastic parts, such as automotive injection molded parts. For low-volume, prototype, and custom production, additive manufacturing is an emerging technology for producing complex thermoplastic parts. When compared to injection molding, the additive manufacturing process fused filament fabrication (FFF) results in an inhomogeneous structure with entrapped air within the volume. Additionally, the presence of short glass fibers in the polymer matrix leads to higher radiation scattering during the welding process. This paper presents a fundamental study of the weldability of additively manufactured fiber-reinforced parts. The specimens were fabricated using a FFF process with glass fiber-reinforced polypropylene (GF-PP). The study investigates the influence of layer thickness and line width of the FFF process on the optical transmittance. LTW-experiments were conducted using additively manufactured uncolored and black GF-PP samples. Lap shear test specimens were welded with a different energy per unit length. This research presents a process for welding additively manufactured GF-PP parts that can be used with optimized FFF-parameters to produce high-strength and durable prototypes or spare parts for the automotive industry. This research provides valuable insights into the process parameters and considerations required to achieve robust welds in additively manufactured thermoplastic parts, facilitating broader adoption of LTW in additive manufacturing contexts.

The hybrid approach of genetic algorithm and particle swarm optimization on reduced weld line defect in plastic injection molding

Weld lines are a serious defect observed in plastic injection molded parts, impacting both their cosmetic appearance and mechanical properties. Controlling the conditions of plastic injection is crucial to mitigate these weld lines. This study introduces a novel approach to identify polypropylene injection molding (PIM) conditions aimed at reducing weld lines in polypropylene parts. The PIM conditions considered in this study include melt temperature, injection pressure, packing pressure, packing time, and cooling time. An orthogonal array Taguchi L27 design was employed for the experimental setup, producing 27 polypropylene parts with varying combinations of process conditions. The width of weld lines generated on the parts’ surfaces was measured using an optimum microscope for all trials. Parametric analysis was conducted using response surface plots and contour plots to estimate the process conditions yielding minimum weld lines. Analysis of variance and regression analysis were employed to interpret the experimental data, with the resulting regression equation used to predict weld lines for a set of PIM process conditions. Finally, two efficient optimization algorithms, genetic algorithm (GA), and particle swarm optimization (PSO), were implemented using MATLAB programming to estimate the optimum process conditions for minimizing weld lines. The GA and PSO predicted weld line widths of 6.12302 μm and 6.123 μm, respectively, representing an 18.51% improvement in results. These findings demonstrate that the novel approach presented in this study can be effectively and reliably applied to address plastic product defects in the industry.

Synthesis of a highly efficient charring agent and its application to intumescent flame‐retardant coatings for 3D‐printed polypropylene parts

AbstractTo improve the flame retardancy of 3D‐printed polypropylene (PP) parts, cyclic triphosphonitrile‐based hyperbranched charring agent (DHCCP) was innovatively synthesized and applied in flame‐retardant coatings. Thermogravimetric analysis (TGA) indicated that the residual char rate of DHCCP reached 64.33% at 700°C. When 5 wt% DHCCP was added to the coating, the limiting oxygen index of the composite reached 29.1%, and the vertical combustion (UL‐94) could reach V‐0 rating. In addition, cone calorimetry test measured a 54.10% reduction in peak exothermic rate, and the tensile strength of coated PP was improved. The morphology and chemical composition of the char residues were investigated by scanning electron microscopy, infrared spectroscopy, and laser Raman spectroscopy. After combustion, the coated PP formed a continuous and dense char layer, which could play the role of heat and oxygen insulation and anti‐drip, effectively improving the flame‐retardant of 3D‐printed PP parts.

Determination of the Effective Fused Deposition Modeling Process Parameters on the Mechanical Properties of Carbon Fiber–Reinforced Polypropylene Parts

Abstract Additive manufacturing is gaining popularity for producing components in industries such as automotive, aerospace, and medicine due to its potential to minimize material waste. Because the strength of the 3-D-printed part is so important, it’s crucial to do research and optimize process parameters to make the printed parts as strong as possible. This work focuses on the experimental investigation and discussion of the tensile and impact strength of parts made from carbon fiber–reinforced polypropylene (PP-CF) using the fused deposition modeling (FDM) technique. Various process parameters, including infill pattern, infill density, layer thickness, and build orientation, are examined on three different levels to determine their influence on the tensile and impact strength of the printed part. The outcomes of the analysis of variance (ANOVA) analysis reveal that infill density primarily affects impact strength, whereas layer thickness significantly influences tensile strength. The optimal combination of parameters leading to the maximum tensile and impact strength consists of a grid infill pattern, 60 % infill density, 0.36-mm layer thickness, and a 45° build orientation. Furthermore, fracture surface analysis is consistent with mechanical test results.

Thermal Expansion of Polypropylene Part II: Depression of In‐Plane Linear Thermal Expansion of Polypropylene by Elastomer Incorporation and Elucidation of Its Mechanism Through Temperature‐Variable X‐ray Scattering

AbstractIn this study, the in‐plane linear thermal expansion behaviors from −20 °C to 100 °C along the flow direction (FD) for injection molded isotactic homo polypropylene (hPP) and their elastomer blends are thoroughly investigated. The elastomers used in this study are two different poly(ethylene‐co‐octene)(EO) thermoplastic elastomers which have the same density but different melt flow rate (MFR), 5.0 and 30 (dg/10 min). Thus, the blends are designated as hPP‐EO5.0 having the EO with 5.0 of MFR and hPP‐EO30 having the EO with 30 of MFR. It is found that from −20 °C to 40 °C, the linear thermal expansion profiles for neat hPP, hPP‐EO5.0, and hPP‐EO30 overlapped, indicating that with or without the EO, their linear thermal expansions proceeded under the same mechanism. On the other hand, above 40 °C, their thermal expansion behaviors greatly changed; the linear thermal expansions of hPP‐EO5.0 and hPP‐EO30 are suppressed to be much lower than that of neat hPP. The morphological observation by a transmission electron microscope (TEM) reveals that the shapes of the EO domains in the blend systems are found to be elongated along the FD. Thus, it would be expected that the suppressed linear thermal expansions of the hPP‐EO blends are attributed to the suppression of the linear thermal expansions of the hPP amorphous layers in the lamellae due to the retraction of the elongated EO domains caused due to the instability of the interfacial tension at elevated temperatures. Yet, temperature variable small‐angle X‐ray scattering (SAXS) results reveal that the linear thermal expansions of the hPP amorphous layers in the EO blends, on the contrary, increase. One of the plausible mechanisms is proposed to elucidate seemingly contradictory phenomenon that the EO blends have their suppressed bulk linear thermal expansions while enhanced linear thermal expansions of the hPP amorphous layers. Finally, the suitable elastomer design for low coefficient of linear thermal expansion (CLTE) PP is proposed.

The influence of saline water immersion tests on the mechanical properties of polypropylene parts produced by additive manufacturing using powder bed fusion technology for subsea application

The influence of saline water immersion tests on the mechanical properties of polypropylene parts produced by additive manufacturing using powder bed fusion technology for subsea application

Rapid tooling of composite aluminium filled epoxy mould for injection moulding of polypropylene parts with small protruded features

Abstract Rapid tooling evolved from rapid prototyping is a novel method for developing prototype tooling rapidly using various additive manufacturing techniques. Traditional injection moulding is unsuitable for low-volume production because of the high initial cost. This study is focused on a rapid tooling approach for producing an injection mould insert for the low-volume production of plastic components. A plastic injection mould insert is designed, developed using composite aluminium filled epoxy with minute protruded features and tested on a vertical injection moulding machine as a rapid tool for low-volume production of plastic components. The composite aluminium filled epoxy (CAFE) mould insert is prepared using a wax master from silicon rubber mould prepared using a stereolithography master. Experiments are performed to determine the optimum mixing ratio of epoxy: aluminium powder for making the composite aluminium filled epoxy injection mould. The mould insert prepared was tested for the injection of polypropylene components on a vertical injection moulding machine and analyzed for dimensional accuracy. The analysis of dimensional accuracy and viability of minute features on the injected parts shows promising results for up to 30 injected parts. The injection of parts after 30 pieces resulted in increasing mould erosion and pitting, causing mould damage at the 36th injection shot. The experimental finding supports the feasibility of using the composite aluminium filled epoxy injection mould for low-volume production of the parts; however, the surface finish is inferior. The life of the mould is expected to give better results with a higher surface finish. It is also exposed that using mould release agents improves the life of the composite aluminium-filled epoxy injection mould.

Braskem mates up with Weav3D for polypropylene parts with thermoplastic composite lattice technology

On September 28, 2023, Braskem, a producer of polyolefins and biopolymers announced a novel demonstrator of Braskem's polypropylene (PP) in combination with WEAV3D Inc., an advanced manufacturing and materials startup, leveraging WEAV3D's thermoplastic composite lattice technology to enhance the performance of PP for structural and automotive material applications.

Thermal expansion of isotactic polypropylene Part I: temperature-dependent contributions of thermal expansions in its amorphous and crystalline phases

Thermal expansion of isotactic polypropylene Part I: temperature-dependent contributions of thermal expansions in its amorphous and crystalline phases

Tribological and Micro-Mechanical Properties of Injected Polypropylene Modified by Electron Radiation

Today, more and more importance is given to the improvement of polymer materials’ wear resistance, i.e., their micro-mechanical and tribological properties, which could widen their application in practice. The properties of materials can be modified by several methods, among them exposure to electron radiation. This study focuses on the effect of varying radiation intensity (15 kGy to 99 kGy), depth of penetration, and subsequent structure modification of injection-molded polypropylene on tribological and micro-mechanical properties. Electron radiation influences the structure of individual layers, thus improving or degrading their properties. Hence, the depth of penetration can be examined by instrumented hardness tests and scratch tests. Due to irradiation, surface properties and wear resistance increased by up to 105% (from 38 MPa to 78 MPa). As the results show, an increase in mechanical properties was recorded in the direction towards the center of the sample (from 72 MPa to 82 MPa). Micro-mechanical tests were also confirmed by the observation of cross-linking changes (gel test) as well as crystallinity increases (wide-angle X-ray diffraction and microtome cuts). This finding could have a significant effect on the manufacturing and subsequent modification of injection-molded polypropylene parts, which opens new possibilities in practice for this material. The increased surface wear resistance enables the use of parts for which the durability and abrasion resistance of the surface are demanded, especially in applications facing exposure to long-term cyclical loads (e.g., gears).

Wetting Characteristics of Laser-Ablated Hierarchical Textures Replicated by Micro Injection Molding

Texturing can be used to functionalize the surface of plastic parts and, in particular, to modify the interaction with fluids. Wetting functionalization can be used for microfluidics, medical devices, scaffolds, and more. In this research, hierarchical textures were generated on steel mold inserts using femtosecond laser ablation to transfer on plastic parts surface via injection molding. Different textures were designed to study the effects of various hierarchical geometries on the wetting behavior. The textures are designed to create wetting functionalization while avoiding high aspect ratio features, which are complex to replicate and difficult to manufacture at scale. Nano-scale ripples were generated over the micro-scale texture by creating laser-induced periodic surface structures. The textured molds were then replicated by micro-injection molding using polypropylene and poly(methyl methacrylate). The static wetting behavior was investigated on steel inserts and molded parts and compared to the theoretical values obtained from the Cassie–Baxter and Wenzel models. The experimental results showed correlations between texture design, injection molding replication, and wetting properties. The wetting behavior on the polypropylene parts followed the Cassie–Baxter model, while for PMMA, a composite wetting state of Cassie–Baxter and Wenzel was observed.

Experimental Analysis on Polypropylene Moulded Part for Performance of Laser Printing

Now a day plastic injection molding is widely used process to manufacture engineering product and consumer goods typically thermoplastic is combined with rubber or another thermoplastic like RM master batch is used to add color to the Molded part also the laser marking on plastic part and their printing cut, faint issue observed. The aim of the study was to Optimize the injection parameters and processing condition for the laser performance on polypropylene part. To achieve enhanced dark laser marking on polypropylene, the process parameter of plastic injection molding and the Raw material master batch mixing parameter successfully prepared this laser–sensitive composite consisted of a high Laser induced carbonization rate.in plastic injection molding use of raw material and mixing of master batch is considerable factor for faint laser marking. Because of laser does not respond well on carbonization added material, it was evident that master batch having the carbon properties is much more responsible for faint laser marking issue on polypropylene material part. The effect of laser beam interaction (Nd: YVO4) with selected operational parameters on the Quality of graphical features obtained on the surface of polypropylene-molded pieces with different surface Textures (variable parameters of the surface layer). Polypropylene test specimens were injection molded using original injection molds Products with variable end parameters determined by the position of the cavity circle can be identified. The layout of the laser function, the beneficiary texture of the molded piece, the molded color and the support of the marking piece allow the evaluation of the graphic symbol performance by means of laser marking of the type of master back in their rendering relationship. Marked evaluation criteria were adopted for the project.

Additive Manufacturing of Carbon Using Commodity Polypropylene.

Carbon materials are essential to the development of modern society with indispensable use in various applications, such as energy storage and high-performance composites. Despite great progress, on-demand carbon manufacturing with control over 3Dmacroscopic configuration is still an intractable challenge, hindering their direct use in many areas requiring structured materials and products. This work introduces a simple and scalable method to generate complex, large-scale carbon structures using easily accessible materials and technologies. 3D-printed, commercial polypropylene (PP) parts can be thermally stabilized through cracking-facilitated diffusion and crosslinking. The newly elucidated mechanism from this work allows thick PP parts to yield carbonaceous products with complex structures through a subsequent pyrolysis step. The approach for enabling PP-to-carbon conversion has consistent product yield and controlled dimensional shrinkage. Under optimized processing conditions, these PP-derived carbons exhibit robust mechanical properties and excellent joule heating performance, demonstrated by their versatile use as heating elements. Furthermore, this process can be extended to recycled PP, enabling the conversion of waste plastic materials to value-added products. This work provides an innovative approach to create structured carbon materials with direct access to complex geometry, which can be transformative to, and broadly benefit, many important technological applications.

An Approach to the Impact Simulation on Foamed Injection Molded Polypropylene Parts: An Example of Application in the Automotive Industry.

An approach to the simulation of foamed injection molded Polypropylene parts subjected to impact loading is presented in this paper. The proposed method, which considers strain-rate-dependent material properties and the possible occurrence of fracture, is, in particular, suitable for parts manufactured with core-back technology. The method was developed to be used within the functionality of a commercial Finite Element solver using a shell-type element mesh. The material model is based on a three-layer structure, with two compact skin layers and a foamed core layer made of expanded material. The properties of the foamed material are assumed as those of the compact grade scaled by a suitable factor, which is identified via inverse engineering on a set of bending tests executed on specimens having different foam densities. The fracture of the material is then predicted using a damage model which considers the effects of triaxiality. The approach is then validated on industrial parts from the automotive sector, subjected to impact in a component test. Despite the simplicity of the presented approach, which makes this method suitable for industrial applications and especially for early-stage design, the validation shows a sufficiently accurate simulation of part behavior under the impact, with a reasonable prediction of damage and fracture.

Investigation of film–substrate interfacial characteristics of polymer parts fabricated via in-mold decoration and microcellular injection molding process

The appearance quality of foamed polymer parts can be improved by introducing high-appearance quality decorative films. However, the interfacial bonding characteristics of film that penetrated the surface of the substrate are few studied. In this paper, the foamed polypropylene (PP) parts with decoration films penetrated on the surface were prepared by the in-mold decoration and microcellular injection molding (IMD/MIM) process. The interfacial characteristics of the IMD/MIM parts were investigated experimentally through peeling tests and interfacial morphology. Based on the finite volume method, the coupled heat transfer model was established to calculate the temperature field in IMD/MIM process by taking into account the coupled heat transfer between polymer melt, film, and mold. The thermal response in the IMD/MIM process was numerically analyzed. The results show that the higher temperature on the polymer melt–film interface corresponds to relatively higher crystallinity and larger crystallite size and also favors the forming of the β-form crystal, which is beneficial to higher adhesion strength. The IMD/MIM parts can obtain a firm film–substrate adhesion and a uniformly strong bond between the film and the substrate.

Modeling and Analysis of Morphology of Injection Molding Polypropylene Parts Induced by In-Mold Annealing

It is generally recognized that high-temperature treatments, namely annealing, influence the microstructure and the morphology, which, in turn, determine the mechanical properties of polymeric parts. Therefore, annealing can be adopted to control the mechanical performance of the molded parts. This work aims to assess the effect of annealing on the morphology developed in isotactic polypropylene (iPP) injection-molded parts. In particular, a two-step annealing is adopted: the polymer is injected in a mold at a high temperature (413 or 433 K), which is kept for 5 min (first annealing step); afterward, the mold temperature is cooled down at 403 K and held at that temperature for a time compatible with the crystallization half-time at that temperature (second annealing step). The characterization of morphology is carried out by optical and electronic scanning microscopy. The temperature of the first annealing step does not influence the thickness of the fibrillar skin layer; however, such a layer is thinner than that found in the molded parts obtained without any annealing steps. The second annealing step does not influence the thickness of the fibrillar skin layer. The dimension of spherulites found in the core is strongly influenced by both annealing steps: the spherulite dimensions enlarge by the effect of annealing steps. A model that considers spherulite and fibril evolutions is adopted to describe the effect of molding conditions on the final morphology distribution along the part thickness. The model, which adopts as input the thermo-mechanical histories calculated by commercial software for injection molding simulation, consistently predicts the main effects of the molding conditions on the morphology distributions.

Optimized injection-molding process for thin-walled polypropylene part using genetic programming and interior point solver

Optimized injection-molding process for thin-walled polypropylene part using genetic programming and interior point solver

Effect of self-nucleation on the crystallization kinetics and the microstructure of polypropylene parts manufactured by Laser Powder Bed Fusion

Laser Powder Bed Fusion (LPBF) of thermoplastic polymers is an additive manufacturing (AM) technique experiencing a remarkable growth in the recent years. Nowadays the most widely used materials are polyamides (PA12, PA11…) but massively available LPBF-compatible polyolefin powders recently arrived on the market. The need of understanding the crystallization process for these new materials is essential and this was addressed in the present work. Isothermal and non-isothermal crystallization kinetics was investigated by differential scanning calorimetry and parts microstructure was analyzed using polarized light optical microscopy, scanning electron microscopy, transmission electron microscopy and wide-angle X-rays diffraction experiments. It was shown that it is important to consider the significant nucleating effect of the sub-surface layers solidification during the building stage. Indeed, half-crystallization times of the PP material are consistent with experimental observations and time range in LPBF only if crystallization occurs from a self-nucleated molten state. Evidence of the presence of nuclei were given thanks to microscopic and wide-angle X-rays diffraction (WAXD) techniques. Alternate patterns of very finely microstructured, oriented transcrystalline regions and isotropic spherulitic regions every 100 µm ( i.e. the layer thickness during printing) were highlighted.

On the temperature evolution and related crystallinity of polypropylene parts processed via material extrusion

This research exposes a new methodology to follow the evolution of polymer crystallinity during material extrusion thanks to the use of thermocouples and fast scanning calorimetry (FSC). Micrometric thermocouples allowed recording the thermal history at different locations on a polypropylene (PP) part, which was then used to reproduce the thermal process conditions in FSC. This method allows to precisely study the evolution of PP crystallinity as function of time, which is an important feature to predict the printability of polymers, since crystallization is known to restrain fusion between beads. The results highlighted the dependence of the periodic thermal stress undergone by PP on several characteristics ( e.g. layer surface area, location in the part, filling strategy). Therefore, the crystallization behavior was found to be different depending on the location in the part. Crystallization was delayed at the center of the part compared to the edges because the nozzle sweep frequency was higher at the center, resulting in lower cooling kinetics. • The evolution of a polymer crystallinity was measured during a production run. • The crystallization kinetics of a polymer depend on the location in the part. • The crystallization kinetics could be controlled by adjusting the deposition pathway. • A partial crystal re-melt was observed during the deposition of successive layers.