Thermoplastic Polypropylene Research Articles

Multi-material fused deposition modelling of structural–functional integrated absorber with multi-scale structure possessing tunable broadband microwave absorption

Designing and manufacturing advanced structural microwave absorbers is one of the most feasible methods to address the growing electromagnetic stealth and protection challenges in both military and civilian domains. To this end, under the application context of structural–functional integration, a series of nanocomposites with varying ratios were prepared using multi-walled carbon nanotubes (MWCNTs) and inexpensive thermoplastic polypropylene as raw materials. The dispersion of nanofillers, rheological properties, thermal properties, and mechanical properties were evaluated. The research found that the impedance matching factor of the electromagnetic wave absorbers plays a more critical role in determining the material’s absorption capacity compared to the loss factor. Simple structural layering by changing the composition and design can effectively increase the effective absorption bandwidth (EAB) of the absorbers, with microwave attenuation primarily arising from conductive loss, interfacial polarization, dipole polarization, and multiple reflections. Finally, a multi-scale quasi-honeycomb absorber was fabricated using multi-material 3D printing with a structured design. Both simulation and experimental results showed consistent trends, demonstrating low sensitivity to the incident azimuth angle. This research features simplicity, low cost, and strong design capability, providing a new strategy for the preparation of functionally graded materials with potential applications in electromagnetic wave absorption.

Multi-functionalization and recycling of basalt fibre/polypropylene laminated composites based on mixed plain-woven fabric and related interfacial decorations

The development of laminated composites of thermoplastic polypropylene (PP)/continuous basalt fabric is limited by poor mutual infiltration and weak interfacial interactions between the matrix and fabric, as well as the intrinsic flammability and susceptibility of the PP matrix to ultraviolet (UV) aging. To solve the above shortcomings in a high-efficiency manner, a multi-functional transition layer was constructed between the PP matrix and long basalt fibres (LBFs) based on a hybrid plain-woven fabric composed of LBFs weft yarns and PP warp yarns. After hot-laminating these hybrid plain-woven prepregs, the mechanical performance of the resultant laminates was optimised and strengthened by selecting the compositions of the multi-functional transition layers (comprising flexible alkyl glycidyl ether chains, various rigid inorganic nanoparticles, or a flexible-rigid hybrid layer). Among these different transition layers, the interface between the LBFs-g-MWCNTs-OH and the PP matrix presented better mutual infiltration due to the lower interfacial energy, stronger mechanical engagement effect derived from the rougher fibre surface, and higher interfacial modulus. Therefore, the fewer structural defects and more effective transfer of the applied load at the interface caused the tensile strength/modulus and flexural strength/modulus of the related hybrid weaving laminates (HWLs) to reach 278.1 MPa/31.8 GPa and 264.2 MPa/12.4 GPa, respectively. The rigid interfaces formed by the deposited nanoparticles also accelerated heat transfer from the matrix to the fibre and the absorption of UV-light inside composite, then improving the flame-retardancy and anti-UV aging performances of the corresponding HWLs. Finally, recyclability evaluations indicated that the waste LBFs-g-SiO2/PP HWLs can be used as anti-UV aging and flame-retardant agents to fabricate new modified PP pellets with multiple functions.

Effects of nanomagnesia and polypropylene-graft-maleic anhydride on the dielectric breakdown properties of polypropylene/ethylene propylene diene monomer blend

Thermoplastic polypropylene (PP) has garnered a significant attention in power cable insulation research because of its exceptional thermal tolerance and dielectric properties. Due to its poor impact strength at room temperature, PP has been blended with various elastomers, including ethylene-propylene-diene monomer (EPDM), to improve the mechanical stiffness of the final material. This, however, comes with compromised dielectric properties of the material. Recently, the addition of nanofillers to polymers has demonstrated promising properties that can be tailored for various dielectric applications, provided that nanofiller and polymer interactions are appropriately formulated. Nevertheless, the effect of nanostructuration in PP/elastomer blends, especially from the perspective of dielectrics, have yet to be systematically explored. In the current work, magnesia (MgO) nanofiller is added to a model PP/EPDM blend system to determine the effect of MgO on the breakdown properties of PP/EPDM. The results show that adding 0.5 wt% of MgO to PP/EPDM reduces the AC and DC breakdown strengths by 7% and 16%, respectively. As the amount of MgO increases to 3 wt%, the AC and DC breakdown strength reduces further by 25% and 29%, respectively. Significantly, appropriate modification of the nanocomposites with polypropylene-graft-maleic anhydride (PP-g-MAH) can result in 5% higher breakdown strength of the nanocomposites with respect to comparable nanocomposites without modification. The mechanisms surrounding these breakdown effects are discussed with the aid of materials structure interpretations. Overall, the results demonstrate that appropriate modification of nanocomposites with PP-g-MAH is crucial in tailoring breakdown properties of PP blend nanocomposites.

Accelerated thermal ageing on performance of polypropylene‐based semiconducting screen for high voltage direct current cable applications—Effect of antioxidants

AbstractThe potential of using eco‐friendly thermoplastic polypropylene (PP)‐based insulation for high voltage direct current (HVDC) cable has been widely investigated but much less work on the PP‐based semiconducting screen (SC). Considering a long service life (>30 years) under high temperature and high electrical stress is required for typical HVDC cables, and investigations on the effect of antioxidant (AO) concentration and thermal oxidative stability, mechanical, and electrical properties of PP‐based SCs have been conducted. It has been demonstrated that an appropriate combination and amounts of AOs are critical for achieving high thermal stability and maintaining the mechanical properties of SC after ageing in a harsh environment (150°C, with Cu, in air, 7 days). Although higher amounts of space charges have been observed in SC/PP/SC samples with higher AO concentrations, the impact on space charge behaviours is less after ageing, suggesting that ageing (or operating at high temperature) leads to microstructure evolution in SC and can potentially mitigate space accumulation in PP‐based insulating materials.

Improved Electrical Properties of Organic Modified Thermoplastic Insulation Material for Direct Current Cable Application.

To achieve exceptional recyclable DC cable insulation material using thermoplastic polypropylene (PP), we have introduced the organic polar molecule styrene-maleic anhydride copolymer (SMA) into PP-based insulation materials following the principles of deep trap modification. PP, PP/SMA, PP/ethylene-octene copolymer (POE), and PP/POE/SMA insulating samples were prepared, and their meso-morphology, crystalline morphology, and molecular structure were comprehensively characterized. The results indicate that SMA can be uniformly dispersed in PP with minimal impact on the crystalline morphology of PP. The DC electrical properties of the materials were tested at temperatures of 30, 50, and 70 °C. The findings demonstrate that the introduction of SMA can improve the DC properties of the material in both PP and PP/POE. The thermal stimulated depolarization current results reveal that SMA can introduce deep traps into the material, thereby improving its DC properties, which is in agreement with the quantum chemical calculation results. Subsequently, a bipolar carrier transport model was employed for coaxial cables to simulate the space charge distribution in the insulation layer of the four sets of insulation samples as well as the actual cable in service. The results highlight that SMA can significantly suppress space charge in PP and PP/POE systems, and it exhibits excellent electric field distortion resistance. In summary, the results illustrate that SMA is expected to be used as an organic deep trap modifier in PP-based cable insulation materials.

Durability of glass fiber reinforced thermoplastic polypropylene composite bars under the coupling effect of seawater and sea sand concrete environment and sustained bending

AbstractThe long‐term interfacial shear strength (IFSS) and flexural strength of GFPP bars under the coupling effect of bending and immersion in the simulated seawater and sea sand concrete (SWSC) solution were studied by an acceleration experiment. Three temperatures and three bending stress levels (0%, 9.8%, and 29.4% of the maximum flexural strain of GFPP bars) were used to accelerate the experiment. Results indicate that the degradation of mechanical properties of GFPP bars is relatively sensitive to the immersion temperature. Low bending stress did not accelerate the degradation of GFPP bars compared with unbent GFPP bars while high bending stress dramatically accelerated the degradation. Microscopic tests found there is corrosion of glass fibers and debonding between glass fibers and polypropylene but no obvious chain breaks of polypropylene occurred. Based on the Arrhenius theory, long‐term stable retention rates of the IFSS of GFPP bars with zero and low bending stress immersed in the simulated SWSC solution are 42.4% and 52.3%.Highlights Low‐stressed GFPP bars degraded similarly or even slower than unbent GFPP bars. GFPP bars degraded mainly due to interfacial debonding and fiber corrosion. Long‐term IFSS of GFPP bars under a coupling effect was predicted.

Investigation of structural parameters of acoustic panels produced from post-industrial textile wastes containing different raw materials

Although noise pollution appears to be a minor issue, it worsens as a result of urbanization and population growth. Unwanted noises have a wide range of negative effects, including anxiety, hostility, high blood pressure, tinnitus, hearing loss, and sleep difficulties. The researchers are compelled to conduct a creative search in order to uncover future environmental solutions due to the noise problem, which is becoming each day worse. Moreover, the textile sector, which is growing day by day, generates huge amounts of waste with the effect of fast fashion trend. The objective of this study is to develop ecofriendly acoustic panels utilizing recycled textile waste and thermoplastic polypropylene (PP) fibers. Within the scope of the study, waste fabrics made of viscose, lyocell, flax, cotton, and polyester are shredded into fibers, and sandwich panels including waste fibers bonded together with PP fibers are generated using the hot press technique. In addition to the use of natural and synthetic fibers, the effects of surface shape (perforated-imperforated) and layer thickness (5 mm and 10 mm) on acoustic performance are examined. The results of the sound absorption and sound transmission loss tests reveal that the acoustic properties of the samples improve as the sample thickness increases, but the perforation process does not have the desired favorable impact on samples of the same thickness. Additionally, the outcomes demonstrate that around 2000 Hz, natural and regenerated fibers with high cellulose content had the best sound absorption coefficients around 0.60. The findings indicate that these eco-friendly panels can be used to reduce unwanted noise in open offices, co-working spaces, and meeting rooms.

Enhancing the mechanical performance of notched glass/epoxy composite laminates via hybridisation with thermoplastic fibres

This study examines empirically and theoretically the open-hole tension and compression characteristics of thermoset composites using hybrid glass/polypropylene and glass/innegra yarns. The Abaqus software, finite element analysis (FEA) has been adopted to predict the tensile and compressive failure loads and damage failure modes for un- and notched samples under tensile and compressive strength tests. The commingling technique was used to create hybrid yarns, which were then transformed into non-crimp preforms before the infusion procedure. It was noticed that the inclusion of thermoplastic polypropylene (PP) and innegra fibres increased the ductility of yarns and composites. Densities of hybrid composites were also reduced by up to 20% when compared to pure glass/epoxy composites. Tensile and open-hole tensile (OHT) test results revealed that hybrid composites are less notch sensitive than glass/epoxy composites due to enhanced composite ductility. For glass composites, having holes resulted in a 41% decrease in tensile strength, compared to reductions of only 25% and 26% for PP and innegra fibre composites, respectively. Further, compression and open-hole compression (OHC) tests presented similar results with OHT tests whilst compressive strength reduction was lower for hybrid composites (10% and 11%) compared to glass/epoxy (28%) ones. The results of the numerical simulation for damage failure modes and tensile and compressive failure loads for un-notch and notched composite laminates are consistent with the experimental findings both qualitatively and quantitatively.

Effect of Surface Coating and Plasma Treatment on Mechanical Properties of Wood Plastic Composites

Mechanical properties of plasma-irradiated and surface-coated wood plastic composites (WPCs) have been investigated in this paper. WPCs were developed by injection molding technique using wood fiber (WF) as reinforcement and polypropylene (PP) as matrix. The short, discontinuous WF was compounded with thermoplastic PP at varying weight fractions of 0 wt%, 25 wt% (WP25), and 50 wt% (WP50) to yield tensile test specimens in accordance with JIS K7139-A32 standards. Subsequently, plasma treatment was performed on the test-pieces, followed by surface coating by immersion in acrylic resin liquid containing homogeneously dispersed TEMPO-oxidized cellulose nanofibers (CNF). The results indicate an increase in surface roughness after plasma irradiation, but surface coating of the specimens with acrylic paint and CNF decreased their surface roughness by ∼50% in comparison to the untreated specimens. Plasma treatment and surface coating also increased the tensile strength of neat PP, WP25 and WP50 specimens by 5.4–7.1%, 3.5–3.7% and 3.0–3.6%, respectively, whereas their fracture strains tended to decrease. Compared to the untreated specimens, the surface-coated specimens generally displayed higher tensile strength. This finding is a corroboration that the observed increase in strength is highly contingent on the adhesion between the specimen surface and the coating layer than on the improvement in surface roughness. Thus, it is inferable that surface coating could be of great importance in enhancing the mechanical performance of WPCs.

EFFECT OF WATER ABSORPTION ON THE MECHANICAL PROPERTIES OF SILANE-TREATED WOOD FLOUR POLYPROPYLENE COMPOSITES

The behavior of the wood flour-polypropylene composites prepared with various contents of untreated and silane-treated wood flour by immersion in water was studied, as well as the effect of the water absorbed by the samples on their mechanical properties. The highest degree of water absorption was observed for the composites containing 30 – 50 mass% alkali pre-treated wood flour. For the materials with 50 mass% untreated, silane-treated and alkali pre-treated wood flour, the water absorption measured was 8.76%, 7.84% and 13.91%, respectively, after 15 days immersion in water. The value of the thickness swelling calculated for the samples prepared with 50 mass% silane-treated wood flour – polypropylene was the lowest – 1.29%. It was proved that the absorption of water molecules results in change of the tensile profile of the thermoplastic polypropylene composites filled with hygroscopic filler.

Statistical tensile and flexural fatigue lives of unidirectional CF/PP laminates

The accelerated testing methodology (ATM) for the statistical life prediction of carbon fiber reinforced plastics (CFRP) under creep and fatigue loads based on the viscoelasticity of matrix resin has been proposed by authors. This method has been successfully applied to the life predictions of unidirectional CFRP with thermosetting epoxy resin as the matrix under tensile and flexural loads. In this paper, this method was applied to the fatigue life prediction of unidirectional CFRP (CF/PP laminates) with thermoplastic polypropylene (PP) as the matrix under tensile and flexural loads, and the effect of matrix viscoelasticity and load cycles on the fatigue behavior of CF/PP laminates were discussed under tensile and flexural loads. First, the viscoelasticity of matrix PP was measured. Second, the static and fatigue strengths of CF/PP laminates were statistically measured at various temperatures and frequencies under tensile and flexural loads. Third, all of material parameters in the fatigue strength formulation in ATM were determined using measured data, and the statistical long-term fatigue strengths of CF/PP laminates were predicted under tensile and flexural loads. As results, comparison with tension and bending test results clarified that the long-term tensile fatigue strength of CF/PP laminates decreases at an accelerated rate as the number of cycles increases, and that the flexural fatigue strength is affected by temperature and frequency rather than by the number of cycles to failure.

Relation between injection molding conditions, fiber length and mechanical properties for highly reinforced long fiber polypropylene

AbstractA complete study on the relation between the injection molding parameters and the resulting fiber length, orientation and mechanical properties is presented for highly reinforced long fiber thermoplastic (LFT) polypropylene (PP). It has been found that the longest fibers obtained are the ones processed with the lowest backpressure and the highest screw speed. The backpressure gains importance over screw speed when the amount of glass fiber reinforcement increases, contrary to what was found for less reinforced thermoplastics. The injection speed does not influence the fiber breakage phenomena, while it has great importance in fiber orientation and thus on the tensile strength, especially when the weight fiber average length is below 1000 μm. When this average is over 1000 μm, fibers begin to weave a mesh that thickens the core region and hinds its orientation, reducing the tensile strength but improving impact resistance.

Multi response optimization of injection moulding process to reduce sink marks and cycle time

In the rapidly growing field of technology, there is a demand for consumer goods made of plastic. To meet needs of customer, plastic products are made in different ways. There are different plastic manufacturing process. Numerous plastic manufacturing process are thereInjection molding is involves injecting molten material into a mold and allowing it to take on the shape of the mold.There are wide ranges of products such as plastic chairs, Computer cabinet etc. are manufactured with the help of smaller and more complex profiles. Due to lack of dimensional accuracy these complex profile produces defects inside the mold. Current study provides insights into transparent thermoplastic Polypropylene products. Five plastic injection molding variable criteria are considered for reducing the depth of sink mark in injection molding for commercial grade transparent thermoplastic (Polypropylene). Melting temperature (8C), mold temperature (8C), packing time (seconds), ratio of ribs to walls (%) and rib to gate distance (mm). According to Taguchi's design L27 experiments are performed and factors are optimized using the Taguchi based utility concept for multi criteria problems. The sink mark's depth on the part's surfaceis considered as quality of product and cycle time is considered as the productivity of product. It is the one of the best techniques, which can maintain the equilibrium between two.

Thermally Resistant, Self-Extinguishing Thermoplastic Composites Enabled by Tannin-Based Carbonaceous Particulate.

Flame-resistant materials are key components in buildings and several other engineering applications. In this study, flame retardancy and thermal stability were conferred to a highly flammable technical thermoplastic—polypropylene (PP)—upon compositing with a carbonaceous tannin-based particulate (CTP). Herein, we report on a straightforward, facile, and green approach to prepare self-extinguishing thermoplastic composites by thermoblending highly recalcitrant particulate. The thermal stability and mechanical properties of the composites are tethered to the CTP content. We demonstrate that the addition of up to 65 wt% of CTP improved the viscoelastic properties and hydrophobicity of the PP, whereas having marginal effects on bulk water interactions. Most importantly, compositing with CTP remarkably improved the thermal stability of the composites, especially over 300 °C, which is an important threshold associated with the combustion of volatiles. PP-CTP composites demonstrated great capacity to limit and stop fire propagation. Therefore, we offer an innovative route towards thermally resistant and self-extinguishing PP composites, which is enabled by sustainable tannin-based flame retardants capable of further broadening the technical range of commodity polyolefins to high temperature scenarios.

Comparative Study of Durability Behaviors of Thermoplastic Polypropylene and Thermosetting Epoxy Exposed to Elevated Temperature, Water Immersion and Sustained Bending Loading.

The long-term degradation of epoxy as the matrix and adhesive serviced in harsh environments plays a key role in engineering applications. Understanding how to improve the toughness and durability of epoxy through reasonable material replacement and design is significant to prolong the service life of engineering structures. In the present paper, thermoplastic polypropylene and thermosetting epoxy were exposed in a coupling environment of elevated temperature, water immersion and sustained bending loading. The evolutions of mechanical and thermal properties were further analyzed and compared. Long-term life prediction was conducted to evaluate the corrosive resistances of polypropylene and epoxy. It can be found that polypropylene has better hydrophobic behavior compared to epoxy. At 80 °C, the ratios of the diffusion coefficient and saturated water uptake between the two matrices were 114.4 and 2.94. At the longest immersion time of 90 days, the degradation percentages of tensile strength were 4.7% (40 °C), 7.5% (60 °C) and 8.8% (80 °C), respectively, which had the higher strength retention (>90%). The maximum strength increase in the multiples of polypropylene/epoxy and polypropylene/polyurethane was 1.95 and 1.75, respectively. The bending loading led to a maximum increase in tensile strength (~1.47%) owing to the oxygen isolation effect. The degradation mechanism was attributed to the active functional groups from the production process reacting with oxygen, resulting in the fracture of the local chain segment. By comparison, water molecules reacted with the hydroxyl groups or interrupted the intermolecular Van der Waals force/hydrogen bond of the epoxy, resulting in irreversible hydrolysis and property degradation. Through the comparison, it can be found that polypropylene and its composites have outstanding properties compared to epoxy, which can make them achieve great application prospects in engineering applications when considering a complex service environment.

Thermally Processed Quantum-Dot Polypropylene Composite Color Converter Film for Displays

Quantum dots (QDs) have attracted much attention as one of the most promising candidates for next-generation display materials. However, stability is still a big challenge for QDs. Herein, we encapsulated QDs in a thermoplastic polypropylene (PP) matrix by thermal processing technology to prepare a stabler color conversion film for the first time. Thermal processing technology expands the packaging materials of QDs from traditional soluble polymers to thermoplastic polymers such as PP with easy processing and a low cost. We showed that the QDs in the PP film exhibited longer-lasting stability than the traditional PMMA film. After 216 h of blue light accelerated aging test, the QDs maintained more than 90% of the initial performance in the PP film but dropped to less than 25% in the PMMA film. Moreover, the reasons for the improved stability have been further discussed. It was found that the PP-H film not only possessed better barriers to moisture and oxygen, but the absence of ester groups also led to a milder environment around the QDs. The results show that ester groups have stronger electronegativity and easily cause the ligands on the surface of QDs to fall off, which lead to performance degradation.

Flexural Strength of Dental Fiber Composite Post Manufactured with a Novel Approach.

Thermoplastic resin fiber composites have an easy fabrication process, good mechanical properties, and compatible stiffness to tooth dentin. However, they have not yet attracted much interest in the field of dentistry. The current study was carried out to test a new proposed approach to manufacture a fiber reinforced composite endodontic post and evaluate its flexural strength through a two-point inclined loading test. The proposed fiber post manufacture approach depends upon a braiding technique of the glass fibers’ (GF) reinforcing component with thermoplastic polypropylene (PP) resin fibers that will later represent the resin matrix after thermal melting. Posts were made of different core (70%) and sheath (30%) construction (PP/GF ratios) using three different GF types and seizing pre-treatment to both fiber types. Two-point inclined loading test at 45 °C applied force angle was used to test the posts’ flexural strength. Fiber posts (1.6 mm in diameter) with pure GF (de-sized starch E-GF and pre-silanized S-GF) core, and sheath construction with higher PP/GF ratios, showed the significantly highest two-point bending strength (56.67 ± 4.89 and 53.96 ± 1.81 MPa, respectively), among experimental posts groups (except for the commercial control posts). However, posts with PP core type showed the lowest values (21.59 ± 1.86 and 16.54 ± 1.94 MPa for de-sized and E-glass sheath fibers, respectively). Based on these findings, the proposed approach was reliable in producing fiber-reinforced composite post with the desired dimensions and fiber distribution. Post construction with a pure GF core and higher PP/GF ratio showed considerably higher flexural strength and GF volume fraction comparable to commercial available post types.

Investigation on effect of semiconducting screen on space charge behaviour of polypropylene‐based polymers for HVDC cables

High voltage direct current (HVDC) power transmission cable is critical for realising sustainability through renewable energy revolution. Eco-friendly thermoplastic polypropylene (PP)-based polymers/nanocomposites are regarded as promising candidates for replacing current thermoset crosslinked polyethylene (XLPE) cables. As an essential component of the extruded HVDC cable for improving conductor/insulation interface and suppressing charge injection to insulation at high DC electrical stresses, developing semiconducting (SC) screens that are compatible with PP-based insulation is of similar importance but has not been well studied yet. This work aims at designing PP-based semiconducting screens and investigating space charge behaviours of SC/PP/SC sandwich specimen to unfold the effect of semiconducting materials, bonding methods, applied DC electric field, and temperature on charge injection, accumulation, transportation, and dissipation in PP-based insulation. Although conventional thermal, mechanical, and low field electrical characterisations demonstrated that all of the developed semiconducting materials meet the performance criteria of commercial semiconducting materials, their space charge and local electric field distribution varied significantly at high DC fields. Compared with the traditional non-bonded configuration used at lab-scale, charge injection was enhanced in hot-pressed SC/PP/SC samples with tightly bonded interfaces, which better reflects the real situation in extruded cables. High temperature further intensified charge injections. Besides, our results also revealed that high temperature and electric field strongly influence charge mobilities and consequently their distribution and local electric field in PP-based insulations.

Low-velocity impact response and infrared radiation characteristics of thermoplastic/thermoset composites

The low-velocity impact response and infrared radiation characteristics of composites have rarely been focused on simultaneously. This study aims to investigate the low-velocity impact response and infrared radiation characteristics of the glass fiber reinforced thermoplastic polypropylene and carbon fiber reinforced thermosetting epoxy resin laminates wildly used in the aircraft industry. The impact tests were conducted at five energy levels. Characterization parameters such as impact load, displacement, and absorbed energy were measured. The damage evolution and damage modes of the laminates were analyzed through active and passive thermography, ultrasonic C-scan, and optical microscope. The results indicate that Thermosets (TS) laminates exhibit better impact resistance, while Thermoplastics (TP) laminates show higher delamination ductility, and the maximum contact force of TP laminates is much smaller than that of the TS laminates under low-velocity impacts, but the low bending stiffness and low ductility of the TP matrix cause the difference in energy absorption level between the two not significant. The temperature characteristic changes of passive infrared thermography heat maps could characterize the damage mode of the laminates. The correlation between the heat maps and the impact characteristic curves is explained; the fluctuation of the impact characteristic curves is directly related to the hot spot characteristics changes of the heat maps. More frequent curve fluctuations correspond to a larger and brighter hot spot on the heat map, which peaks at the maximum impact load after the impact force versus time curve fluctuation cutoff point, the maximum center displacement of the impact force versus displacement curve, and the maximum absorbed energy of the absorbed energy versus time curve.

Scalable Fabrication of Microcellular Open‐Cell Polymer Foams

Open‐cell foams are foams with porous, interconnected cellular structure. This unique structure has given open‐cell foams the versatility to be used in different types of applications including acoustics, filtration, membranes, and bioscaffolds. Conventional open‐cell polymer foams comprise mainly thermosetting and/or crosslinked materials; such materials are difficult to process and have limited end‐product recyclability. This article presents a commercially viable molding process to fabricate open‐cell foams using noncrosslinked thermoplastic polypropylene (PP). Highly open‐cell and/or reticulated structures at an open‐cell content of 84% are attained. The strategies employed in molding of PP foam with high open‐cell degree include: 1) use of mold‐opening method to achieve high void fractions; 2) reduction of cell‐wall thickness through increasing the cell densities via controlled crystallization; and 3) use of low viscosity or low melt‐strength polymer resins to promote cell‐wall opening. The molding process proposed may be extended to other semicrystalline thermoplastic materials for fabricating recyclable open‐cell foams.