Foam Injection Molding Research Articles

Influence of plasticisation during foam injection moulding on the melt viscosity and fibre length of long glass fibre-reinforced polypropylene

Abstract The processing of long glass fibre-reinforced thermoplastics results in considerable fibre damage, particularly during plasticising. By using thermoplastic foam injection moulding (FIM) with a constant blowing agent atmosphere, fibre damage during plasticisation can be reduced. This can be attributed to the reduction of the melt viscosity on the one hand and the influence of the melting behaviour on the other. Therefore, the influence of the FIM and the process parameters on the fibre length and the fibre length distribution are analysed and compared with the influence of the process parameters on the melt viscosity.

A Method of Simulating the Dissolution Behavior of Physical Blowing Agents. Dissolution Behavior of Physical Blowing Agent in Low-pressure Foam Injection Molding Process (Part 2)

A Method of Simulating the Dissolution Behavior of Physical Blowing Agents. Dissolution Behavior of Physical Blowing Agent in Low-pressure Foam Injection Molding Process (Part 2)

Forefront Research of Foaming Strategies on Biodegradable Polymers and Their Composites by Thermal or Melt-Based Processing Technologies: Advances and Perspectives.

The last few decades have witnessed significant advances in the development of polymeric-based foam materials. These materials find several practical applications in our daily lives due to their characteristic properties such as low density, thermal insulation, and porosity, which are important in packaging, in building construction, and in biomedical applications, respectively. The first foams with practical applications used polymeric materials of petrochemical origin. However, due to growing environmental concerns, considerable efforts have been made to replace some of these materials with biodegradable polymers. Foam processing has evolved greatly in recent years due to improvements in existing techniques, such as the use of supercritical fluids in extrusion foaming and foam injection moulding, as well as the advent or adaptation of existing techniques to produce foams, as in the case of the combination between additive manufacturing and foam technology. The use of supercritical CO2 is especially advantageous in the production of porous structures for biomedical applications, as CO2 is chemically inert and non-toxic; in addition, it allows for an easy tailoring of the pore structure through processing conditions. Biodegradable polymeric materials, despite their enormous advantages over petroleum-based materials, present some difficulties regarding their potential use in foaming, such as poor melt strength, slow crystallization rate, poor processability, low service temperature, low toughness, and high brittleness, which limits their field of application. Several strategies were developed to improve the melt strength, including the change in monomer composition and the use of chemical modifiers and chain extenders to extend the chain length or create a branched molecular structure, to increase the molecular weight and the viscosity of the polymer. The use of additives or fillers is also commonly used, as fillers can improve crystallization kinetics by acting as crystal-nucleating agents. Alternatively, biodegradable polymers can be blended with other biodegradable polymers to combine certain properties and to counteract certain limitations. This work therefore aims to provide the latest advances regarding the foaming of biodegradable polymers. It covers the main foaming techniques and their advances and reviews the uses of biodegradable polymers in foaming, focusing on the chemical changes of polymers that improve their foaming ability. Finally, the challenges as well as the main opportunities presented reinforce the market potential of the biodegradable polymer foam materials.

Development of toughened and heat-resistant biodegradable injection-molded polylactide acid-based blend foams via enhancing interfacial bonding and PLA phase crystallization

Polylactic acid (PLA) foam is gaining increased attention as a biodegradable alternative to traditional petroleum-based plastic foams, which pose significant environmental pollution issues post-use. However, its potential application is greatly limited by inherent shortcomings such as brittleness and diminished heat resistance post-melting. Herein, high-performance biodegradable PLA/poly(butylene succinate) (PBS) blend foams with well-defined cell structure, high ductility, and enhanced heat resistance were fabricated using a core-back foam injection molding (FIM) process coupled with a straightforward annealing procedure. To enhance compatibility and tailor the dispersed phase morphology into a more fibrillar structure, an epoxy-functional chain extender (ADR) was incorporated. This addition resulted in a substantial increase in the notched impact strength, elevating it to 7.0 kJ/m2, compared to the mere 1.5 kJ/m2 of unmodified PLA foam. Moreover, with the inclusion of 1.0 phr ADR, the notched impact strength of the foam post-annealing soared to 20.7 kJ/m2, a 13.8-fold enhancement compared to pure PLA foam. The formation of a uniformly distributed and interlocked “shish-kebab" crystal structure in the blend facilitated effective stress transfer and distribution, leading to shear yield in the PLA matrix. Additionally, the heat deflection temperature of the annealed blend foam showed a significant increase significantly to 94.7 °C, in contrast to the mere 55.6 °C of pure PLA foam. This study demonstrates a viable and feasible strategy for preparing fully biodegradable PLA foams with high-toughness and heat resistance.

Dissolution Mechanism of Physical Blowing Agent into the Polymer in Low-pressure Physical Foam Injection Molding Process (Part 1) Effect of Molding Conditions on Physical Blowing Agent Concentration

Dissolution Mechanism of Physical Blowing Agent into the Polymer in Low-pressure Physical Foam Injection Molding Process (Part 1) Effect of Molding Conditions on Physical Blowing Agent Concentration

Lightweight and High Mechanical Properties of In Situ Poly(ethylene terephthalate) Reinforced Polypropylene Composite Foams by Chemical Foam Injection Molding

Lightweight and High Mechanical Properties of In Situ Poly(ethylene terephthalate) Reinforced Polypropylene Composite Foams by Chemical Foam Injection Molding

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) microcellular foams using a melt memory effect as bubble nucleation sites

AbstractPoly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBH) foams were prepared by a foam injection molding (FIM) process using nitrogen (N2) as a physical blowing agent. PHBH is a marine degradable polymer known for its heat treatment weakness. Gel permeation chromatography and rheological measurements showed that the molecular weight was reduced when the polymer was processed at a temperature higher than 160°C; however, it had a prominent melt memory of crystallization at a temperature lower than 170°C. The melt memory effect increased the crystallization temperature and provided crystal nucleation sites, which became bubble nucleation sites in the foaming process. Microcellular foams, whose cell size is smaller than 30 μm and cell density is higher than 3 × 108 cells cm−3, were prepared using the melt memory effect while suppressing the thermal decomposition by tuning the injected polymer's temperature (melting temperature) and the core‐back timing. The mechanical properties of the resulting foams were evaluated, indicating that a high ductility PHBH microcellular foam was obtained at a melting temperature of 150°C.

Study on the Flow, Foaming Characteristics and Structural Strength of Polypropylene Structural Foam Injection Molding by Innovative Nitrogen and Molten Plastic Mixing Mechanism.

Plastic foam molding methods include thermoforming, extrusion and injection molding. Injection foam molding is a one-time molding method with high production efficiency and good product quality. It is suitable for foamed plastic products with complex shapes and strict size requirements. It is also the main method for producing structural bubbles. In this investigation, we developed a structural foam injection molding technology using the gas supply equipment connected to the unique plasticizing mechanism of the injection machine and studied its influence on the specimens' melt rheology quality and foam structures. In the experiment, the forming material was polypropylene (PP), and the gas for mixing/forming foaming characteristics was nitrogen (N2). Additionally, in order to observe the rheological properties of N2/melt mixing, a melt flow specimen mold cavity was designed and the change in the melt viscosity index was observed using a melt pressure sensing element installed at the nozzle position. With the nitrogen supply equipment connected to a unique plasticizing mechanism, the mixing of gas and molten plastic can be achieved at the screw plasticizing stage, where the foaming effect is realized during the melt-filling process due to the thermodynamic instability of the gas. It was also found that an increase in N2 fill content increased melt fluidity, and the trend of melt pressure and melt viscosity index showed that the higher the gas content, the lower the trend. The foaming characteristic depends on the gas thermodynamic instability and the pressure release, so it can be seen from the melt fill path that, the greater the pressure near the gate, the lower the foaming amount and the internal structure (SEM) after molding; the farther from the gate, the greater the relative increase in the foaming growth/amount. This phenomenon will be more obvious when the N2 fill content is increased.

Physical and Chemical Foam Injection Moulding of Natural-Fibre-Reinforced Polypropylene—Assessment of Weight-Reduction Potential and Mechanical Properties

Reducing weight not only consumes fewer resources for manufacturing but also requires less energy for transportation, thus preserving resources and reducing CO2 emissions. The latter part is of utmost importance in mobility applications. For example, in the automotive industry, the large-scale production of lightweight structural parts is becoming a main issue. An effective method to meet these requirements is foam injection moulding. In this study, physical (MuCell technology) and chemical foam injection moulding was used to produce plates made from wood-fibre- and cellulose-fibre-reinforced polypropylene, respectively. For both technologies, the used core-back method enabled precise mould opening during injection and thus allowed for variation in the plate thickness and density. The simpler short-shot technology, used only for the chemical foaming trials with differing shot volumes, provided plates with constant thicknesses. The foam structure and finally the mechanical properties of the plates depended on the filler type, the foaming method and the density. The latter was directly linked to either the plate thickness or the shot volume. Physical foaming appeared to be slightly more effective regarding the achievable density reduction (up to 37% reduction), but the physically foamed parts had worse mechanical properties at equal density than their chemically foamed counterparts. Besides the comparison of different foaming methods, this study provides the tensile, flexural and impact properties of natural-fibre-reinforced polypropylene composites over a wide density range, thus offering a good basis for evaluating weight-saving potential for various applications.

In-Line Monitoring of the Physical Blowing Agent Concentration by Transmission Near-Infrared Spectroscopy with High-Pressure Resistance Fiber Optic Probes for Foam Injection Molding Processes

In-Line Monitoring of the Physical Blowing Agent Concentration by Transmission Near-Infrared Spectroscopy with High-Pressure Resistance Fiber Optic Probes for Foam Injection Molding Processes

Significantly Improved Foamability and Mechanical Properties of Polypropylene through a Core–Shell Structure via Low Gas Pressure Foam Injection Molding

Lightweight plays an important role in energy conservation and emission reduction. Foam injection molding (FIM) is a promising technology for the mass preparation of structural parts. But it is still a challenge to prepare foam with good cellular structure via low gas pressure foam injection molding (LGP-FIM). Polypropylene (PP) as a kind of universal plastic exhibits good mechanical properties, but its mechanical properties are notably deteriorated after foaming. In this study, ethylene-propylene-diene monomer (EPDM) rubber and high-density polyethylene (HDPE) were added to PP to improve its melt strength and increase the gas diffusion rate. As a result, the cell size of the ternary blend attained was ∼2 μm, and the cell density was increased to 1010 cells/cm3. Meanwhile, the tensile toughness of ternary blend foam increased by 668% compared to PP foam. The notched impact strength of ternary blend foam increased by 178% compared to PP foam. Considering the excellent performance of PP foam and the low cost of LGP-FIM, this work presents a method for fabricating high mechanical performance foams that could be easily industrialized.

From the perspective of cells as dispersed phase in foam injection molding: Cell deformation of PP/PTFE foams

The objective of the present work was to study deformation of cells of polypropylene/polytetrafluoroethylene (PP/PTFE) composite foams prepared via foam injection molding (FIM) with supercritical nitrogen (N2) as foaming agent. Different contents of N2 and various contents of PTFE were applied as variables to study the cell deformation in the flow direction. Scanning electronic microscope (SEM) was used to study the cell structure. It is found that the increase in both contents of N2 and PTFE were favourable for deformation of the cells. With the increase in both the contents of N2 and PTFE, the cell density increased, the cell size in short axis decreased, and the change in cell size in long axis depended on the cell structure being upon deformation or not. The deformation of the cells was signified by an abrupt increase of cell size in long axis and the ratio of cell size in long axis to short axis being larger than one. It is then found that the cell deformation in this study occurred unexpectedly with the increase in cell density. This is attributed to the fact that the increase in either N2 or PTFE content increases both the cell density and the tendency of cell deformation. This study has brought a new perspective to study the cell deformation in FIM via regarding cells as dispersed phase, and will provide experimental support for preparation of foams with oriented cells in the future.

Cavity pressure profile study during foam injection molding and its effect on cell formation of polypropylene/chemical blowing agent foam

AbstractIn the current scenario, many automotive and aerospace industries have exaggerated replacement of most of the metal parts with polymers to achieve the pursuit of lightweight thereby to reduce fuel consumption and carbon emission. Foam injection molding (FIM) is among one of the cost‐effective approaches to produce lightweight polymer products. During FIM, stringent control over various processing parameters is crucial to ensure the precision and reliability of molded parts. This work aims toward the investigation of cavity pressure and its effect on microstructure or cell morphology in chemical blowing agent mixed polypropylene (PP) foams produced by FIM. In particular, effect of varying injection temperature, injection speed and plasticization parameters (screw rotation speed and back pressure) have been examined on the cavity pressure profiles and its conforming influence on cell nucleation and growth have been discussed acutely. The results of this study indicate that various process parameters significantly influence the trajectory of cavity pressure profile during FIM which in turn critically decides structural uniformity of foamed product.

Structure-property-relationships for Lightweight Parts Produced via Co-injection Molding and Foam Injection Molding

Structure-property-relationships for Lightweight Parts Produced via Co-injection Molding and Foam Injection Molding

Strong and high void fraction PP/CNS nanocomposite foams fabricated by core‐back foam injection molding

AbstractPolypropylene/carbon nanostructure (PP/CNS) nanocomposite foams with a void fraction as high as 78% were successfully prepared by foam injection molding (FIM) with core‐back operation. Rheological curves and differential scanning calorimetry results showed that the added CNS significantly improved the melt strength and accelerated the crystallization process of PP, respectively. A high mold temperature was applied to overcome the adverse effect of CNS, which had a high thermal conductivity and went against the preparation of high void fraction (VF) products. Thus, adding CNS could dramatically increase cell density by three orders of magnitude. With a CNS loading of 5 wt%, the PP/CNS nanocomposite foam with a cell size of about 60 μm, cell density over 107 cells/cm3, and a void fraction of 78% was obtained. More interestingly, the specific flexural modulus of the PP/CNS composite foam with 50% void‐fraction was increased by 37% relative to the neat solid injection‐molded PP. PP/CNS composite foams with adjustable cell structure and good mechanical properties show great potential for electromagnetic interference (EMI) shielding and sensors applications.

Development of New Foam Injection Molding Technology and Its Potential

Development of New Foam Injection Molding Technology and Its Potential

Lightweight and High Impact Polypropylene Foam Fabricated via Ultra‐Low Gas Pressure Injection Molding

AbstractFoamed materials play an important role in a lightweight design. Foam injection molding (FIM) is an advanced and convenient way to fabricate lightweight structural materials. Recently, a new foam injection molding machine is developed, which only needs ultra‐low gas pressure to fabricate microcellular foam. As a universal plastic, polypropylene (PP) is widely used due to its good mechanical properties. But after foaming, the toughness of the PP tends to decrease. Herein, a lightweight and high‐impact polypropylene foam is fabricated via the new FIM technology with an ultra‐low nitrogen pressure of 6.5 MPa. PP/polyolefin elastomer (POE) foam with a tiny cell size of 4.13 µm and high cell density of 2.7 × 109 cm−3 is successfully obtained. Owing to the superior cellular structure, compared with the pure PP foam, after adding the POE component, the maximum impact performance is increased by 465%. In this work, an easy‐to‐industrialized method for preparing lightweight and high‐impact injection‐molded PP foams are presented.

Tunable electromagnetic interference shielding performance of polypropylene/carbon black composites via introducing microcellular structure

The introduction of cell structures in conductive polymer composites (CPCs) has considerable impacts on electromagnetic interference (EMI) shielding performance of the final CPC foams, and thus it is necessary to clarify the effects of cell structures on the shielding effectiveness (SE) and mechanisms of CPC foams with different filler loadings and expansion ratios more systematically. Herein, polypropylene (PP)/carbon black (CB) composite foams were prepared by core-back foam injection molding (FIM), and their cell structures were well-controlled by changing the CB content and expansion ratio. The results showed that, at different CB contents, the surface EM reflection of all PP/CB foams decreased with increasing the expansion ratio, while their SE values exhibited different trends possibly owing to the changes of sample thickness as well as internal multiple EM reflections/scattering, interfacial polarization and conductive loss during EMI shielding. The EMI SE declined with the increase of expansion ratio for the PP/CB foam with low CB content of 10 wt%, but it was improved for the foam with high CB content of 30 wt%. At a middle CB content of 22.5 wt%, however, the EMI SE of the PP/CB foam first decreased and then increased with the increase of expansion ratio. Our study provides an efficient method to tune the EMI-shielding properties of CPC foams without changing the material weight.

Lightweight and tough PVDF foams via high‐pressure foam injection molding with core‐back operation

AbstractPolyvinylidene fluoride (PVDF) foams prepared by batch foaming have been intensively studied, but it still remains a challenge to fabricate high‐performance PVDF foams for structural applications. Herein, by adding polymethyl methacrylate (PMMA) as the minor component, the blend foams were successfully fabricated using supercritical carbon dioxide (CO2) as a green blowing agent via foam injection molding (FIM) with core‐back operation. The added PMMA could reduce the crystal size of PVDF. Owing to fine cellular structure and small crystal sizes, the injection‐molded blend microcellular foams exhibited superior mechanical properties. Especially, the elongation at break and specific breaking energy of the blend foam with 40% void fraction were separately increased by 184% and 297% compared to that of the PVDF foam. These findings revealed that the lightweight microcellular PVDF foams with improved toughness could be manufactured by the scale‐up and efficient FIM technology, which showed a promising future in automotive and other structural applications.

A Design Tool for Core-Back Timing in Foam Injection Molding

A Design Tool for Core-Back Timing in Foam Injection Molding