PP Foams Research Articles

Ethiopian Bamboo Fiber Aging Process and Reinforcement: Advancing Mechanical Properties of Bamboo Fiber-Epoxy Composites for Automobile Applications

The purpose of this paper is to evaluate the properties of Ethiopian bamboo fibre polymer composites as headliners in the automobile industry. Bamboo fibres are developed using the roll milling technique, and bamboo fibre epoxy composites (BFEPCS) are developed using a compression mould and a hot press machine. The mechanical properties are measured based on the recommended procedure of the ASTM. In total, 40% of the volume fraction of fibres is used to produce polymer composites. An accurate evaluation of its mechanical properties is thus critical for predicting its behaviour during a vehicle’s interior impact assessment. Conventional headliner materials are heavier, non-biodegradable, expensive, and non-sustainable during processing compared to the currently researched materials. Three representatives of bamboo plants are harvested in three regions of bamboo species, three groups of ages, and two harvesting months. Two-year-old bamboo fibres have the highest mechanical properties of all ages, and November has a higher mechanical properties compared to February. Inji-bara and Kom-bolcha have the highest and lowest mechanical properties, respectively. BFEPCs have high mechanical properties compared to BFPPCs. The mechanical properties of the current research findings have higher measured values compared to Jute felt PU, CFPU, GFMPU, BFPP, BFEP, PP foam, and TPU. The flexural strength of BFPCs has higher properties compared to their tensile strength. Ethiopian bamboo fibres and their polymer composites have the best mechanical properties for the composite industry, which is used for headliner materials in the automobile industry, compared to conventional headliner materials.

Study on properties of BF/PP composites and plastic parts manufacturing by mold opening foaming injection molding

Basalt fiber (BF), as an emerging natural and environmental-friendly material, possesses a broad application prospect. Herein, lightweight and strong BF reinforced polypropylene (BF/PP) composite foams were successfully prepared using mold opening foam injection molding (MOFIM) technology. It was revealed that the combination of increased crystallinity and enhanced rheological behavior in turn contributes to the improved foaming behavior of 20%BF/PP, which reduces the cell size of PP to 36.38 μm and boosts the cell density by a factor of 2 under an expansion ratio of 1.2. The improvement effect of BF on cell structure is more obvious at higher expansion ratio. This fine and dense cell structure further augments the impact performance and flexural modulus of BF/PP composite foams. Compared to pure PP, 20%BF/PP composite foams experienced an increasement of impact performance, which is increased by 68.8% to 2.7 kJ/m2, and its flexural modulus also elevated significantly by 224.8% to 2440.25 GPa. Due to its excellent weight reduction effect, the specific impact strength and specific flexural modulus remain at much higher levels than those of PP foam. This indicates that BF and MOFIM technique successfully prepared a ductile material with excellent impact resistance, modulus and thermal insulation properties.

Preparation of clay-supported sodium benzoate and its effect on the rheology, crystallization and foaming of long chain branched polypropylene

The foaming of PP has encountered challenges because of its low melt strength and semi-crystalline characteristics. Introducing long chain branching (LCB) onto the PP backbone and the addition of particles as cell nucleating agent are the commonly used methods to improve the cell structure of PP foams. In this paper, clay-supported sodium benzoate (NaB-OMMT) was prepared from Na-montmorillonite (Na-MMT) via the partial ion exchange reaction with surfactant and subsequent reaction with benzoic acid. The as prepared NaB-OMMTs were then applied to prepare LCBPP/NaB-OMMT nanocomposites and their foams. The dispersion state of clay, crystallization behaviors and rheological properties of the nanocomposites, as well as the cell structure and compression properties of the foams were investigated. The results show that clay layers are mostly exfoliated in the nanocomposites with low NaB-OMMT content, while intercalated layers dominant with the content reaches 2% or higher. The melting temperature of the nanocomposites decreases and the crystallinity increases, while the spherulite size decreases compared to LCBPP. The melt viscosity and elasticity of nanocomposites increase significantly when the content of NaB-OMMT reaches 2% or higher. LCBPP/NaB-OMMT nanocomposites foams exhibit higher cell density, smaller cell size and its standard deviation. Therein, the foam with 1% of NaB-OMMT shows the maximum cell density and the minimum cell size. It is concluded that the cell structure of the foam is highly dependent on the content, dispersion state and structure of the cell nucleating agent. When NaB is supported on well dispersed and exfoliated clay layers, the cell nucleation efficiency is significantly enhanced. The compression properties of the foams depend on their cell structures and exhibit the similar variation trend with the latter with the content of NaB-OMMT increasing.

Mechanism of Low‐Temperature Brittle–Ductile Transition of Polypropylene/Low‐Density Polyethylene Blend Foam under Compressive Stress Caused by Cell Stretching

To enhance the low‐temperature toughness of polypropylene/low density polyethylene (PP/LDPE) blend, which is a crucial blend for polyolefin material with wide applications in frigid regions, the PP/LDPE blend foam with stretched cells is fabricated via a facile injection foaming together with open‐mold stretching process. During the open‐mold stretching, the relatively miscible PP and LDPE chains are debonded, and then the stretched and oriented cells structure with lots of tiny interphase cavities between the PP and LDPE phases and the fine lamellae are formed in the foam system. Such interphase cavities provide an adequate movement space for the frozen PP and LDPE chains and lamellae, and effectively relaxed and transferred stress, which greatly promote the uniform compressive behavior accompanied by the completely compacted cells at −25 °C. Moreover, the compressive fracture surface changes from relatively flat and smooth for the stretched PP foam to obvious yield folds and deformation for the stretched blend foam, and the compressive strain of stretched PP/LDPE blend foam is highly enhanced by a roughly 31%, 53%, and 44% increase than that of PP, PP/LDPE, and stretched PP foam samples, respectively, achieving the low‐temperature brittle–ductile transition for PP.

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.

Lightweight and strong glass fiber reinforced polypropylene composite foams achieved by mold-opening microcellular injection molding

Microcellular injection molding (MIM) is a flexible, efficient, and environmentally friendly foaming technology to prepare plastic foams with complex shapes. However, MIM product suffers from deteriorated mechanical properties, limited weight reduction, and poor surface appearance. In this study, mold-opening microcellular injection molding (MOMIM) was used to prepare high-performance polypropylene/glass fiber (PP/GF) composite foams. GF was used to improve the foaming behavior of PP and to enhance the mechanical properties of foamed samples. Firstly, the crystallization and rheological behavior of PP and PP/GF were analyzed. Afterwards, the foaming behavior of PP and PP/GF in microcellular injection molding process were investigated. Finally, the mechanical properties of PP and PP/GF foams were measured and discussed. It was found that PP/GF composite foams show a rather uniform cellular structure than the pure PP foams. Moreover, PP/GF composite foams exhibit much higher strength and stiffness than the pure PP foams. Furthermore, MOMIM can significantly enhance the flexural modulus of the molded samples. For the foams with an expansion ratio of 1.5-fold, by adding 20 wt% GF, the tensile strength and modulus can be increased by 60% and 50%, respectively. For the PP/GF composite with 20 wt% GF, the foamed sample prepared by MOMIM can have a flexural modulus nearly 200% higher than that of the unfoamed sample. Thus, MOMIM PP/GF composites show a promising perspective in providing lightweight and strong plastic products that can be widely used in automotive, electronics, and appliances.

Improved Cell Morphology and Surface Roughness in High-Temperature Foam Injection Molding Using a Long-Chain Branched Polypropylene.

Long-chain branched polypropylene (LCB PP) has been used extensively to improve cell morphologies in foaming applications. However, most research focuses on low melt flow rate (MFR) resins, whereas foam production methods such as mold-opening foam injection molding (MO-FIM) require high-MFR resins to improve processability. A systematic study was conducted comparing a conventional linear PP, a broad molecular weight distribution (BMWD) linear PP, and a newly developed BMWD LCB PP for use in MO-FIM. The effects of foaming temperature and molecular architecture on cell morphology, surface roughness, and mechanical properties were studied by utilizing two chemical blowing agents (CBAs) with different activation temperatures and varying packing times. At the highest foaming temperatures, BMWD LCB PP foams exhibited 887% higher cell density, 46% smaller cell sizes, and more uniform cell structures than BWMD linear PP. Linear PP was found to have a surface roughness 23% higher on average than other resins. The BMWD LCB PP was found to have increased flexural modulus (44%) at the cost of decreased toughness (−88%) compared to linear PP. The branched architecture and high molecular weight of the BMWD LCB PP contributed to improved foam morphologies and surface quality in high-temperature MO-FIM conditions.

Effect of crystalline structure on the cell morphology and mechanical properties of polypropylene foams fabricated by core‐back foam injection molding

AbstractFoam injection molding (FIM) is an advanced technology for preparing lightweight plastic foams, but its inferior mechanical performance remains a challenge. In this study, microcellular injection‐molded β‐polypropylene (β‐PP) foams with high ductility were successfully prepared by combing the β‐nucleating agent with controllable temperature field. Foaming results showed that the microcellular β‐PP foams exhibiting a cell size of about 8 μm and cell density over 108 cells/cm3 were prepared with a crystalline diameter approximately 5 μm, while PP foams had a rather large cell size approximately 150 μm and low cell density of 105 cells/cm3 with 30 μm crystalline size. As a result, this significant improvement in cell structure as well as the crystalline size lead to a significant increment of 86% for the ductility of β‐PP foams. This work offers a facile strategy to prepare injection‐molded foams with desirable mechanical properties for their wide range of applications, such as automotive construction and consumer electronics.

Effect of alcohols-regulated crystallization on foaming process and cell morphology of polypropylene

A novel approach was established to promote favorable PP foams at low temperatures by regulating the melt crystallization behavior. The crystallization behavior of PP on supercritical CO2 foaming was systematically studied in the presence of alcohol as co-blowing agent. The results of dissipative particle dynamics (DPD) simulations revealed that the diffusion coefficient of blowing agents in PP was enhanced with the increase of alcohol molecular weight. Alcohols had a significant effect on the melt and crystallization behavior of PP. The crystallization temperature was decreased from 88 ℃ to 82 ℃, and crystallinity declined from 17% to 9% by adding 1-decanol in 8 MPa CO2. The addition of co-blowing agents decelerated desorption rate of blowing agents. The lower limit of foaming temperature moved further down with the carbon chain growth of alcohol, e.g., the lower temperature decreased from 145 ℃ to 130 ℃ by adding 1-decanol.

Purification of Waste Water from Petroleum Products with the Use of Combined Sorbents

The results of the study on the purification of model water from petroleum products with the concentration of 15 to 100 mg/dm3with the use of polyethylene foam (PE foam) and polypropylene foam (PP foam) polymer chips a well as the carbon ABZ sorbent as sorbents were presented. The sorption process was carried out under dynamic conditions. The model waters were purified with PE foam and PP foam polymer chips, the purification efficiency was up to 91%. To increase the purification efficiency of model waters from petroleum products, the model solutions were purified from petroleum products through a combined loading - PE foam chips and ABZ sorbent. It is shown that the use of a combined loading allows to reduce the concentration of petroleum products in waste water to standard values. The results of chromatography - mass spectrometric analysis confirm the high efficiency of waste water purification from petroleum products.

Microplastic pollution and ecological risk assessment in an estuarine environment: The Dongshan Bay of China

Microplastic (MP) pollution has spurred a wide range of concerns due to its ubiquity and potential hazards to humans and ecosystems, yet studies on MP abundance, distribution, and ecological impacts on the small-scale local estuarine systems are insufficient. We conducted the first study of MP pollution in surface water of Dongshan Bay in southern China. A total of six water samples were collected using a Manta trawl (length = 3 m, width = 1 m, height = 0.6 m, and mesh size = ∼330 μm). The abundance, type, shape, color, and size, were measured using light microscopy and micro-Raman spectroscopy. Our results showed that MPs spanned from 0.23 to 4.01 particles m−3 with an average of 1.66 particles m−3. 75% of the MPs were PP, PE, and PS that may be explained by the widespread application of PE, PP, and PS foam in local fishing and aquaculture within the bay. Foam, white, and 1.0˗2.5 mm were dominant shape, color, and size of MPs, respectively. Both indices of MPs-induced risk (Hestuary = 13.7) and pollution load (PLIestuary = 14.2) yielded a Hazard Level II for MPs pollution in the Dongshan Bay. The potential ecological risk from combined MPs polymers (RIestuary = 21.5) ended up at a minor risk. Our findings established the first set of baseline data on MPs pollution in Dongshan Bay and provided preliminary quantitative measures on the scale of ecological risk, which would improve the understanding of MP fate, transport, and ecological impacts in the estuarine environment.

Improving the Supercritical CO₂ Foaming of Polypropylene by the Addition of Fluoroelastomer as a Nucleation Agent.

In this study, a small amount of fluoroelastomer (FKM) was used as a nucleating agent to prepare well-defined microporous PP foam by supercritical CO2. It was observed that solid FKM was present as the nanoscale independent phase in PP matrix and the FKM could induce a mass of CO2 aggregation, which significantly enhanced the diffusion rate of CO2 in PP. The resultant PP/FKM foams exhibited much smaller cell size (~24 μm), and more than 16 times cell density (3.2 × 108 cells/cm3) as well as a much more uniform cell size distribution. PP/FKM foams possessed major concurrent enhancement in their tensile stress and compressive stress compared to neat PP foam. We believe that the added FKM played a key role in enhancing the heterogeneous nucleation, combined with the change of local strain in the multiple-phase system, which was responsible for the considerably improved cell morphology of PP foaming. This work provides a deep understanding of the scCO2 foaming behavior of PP in the presence of FKM.

Lightweight and strong microcellular injection molded PP/talc nanocomposite

Lightweight is of great significance for reducing material and energy consumptions. Microcellular injection molding is an advanced technology for fabricating lightweight plastic structural components, but the deteriorated mechanical performance is a big challenge. In this study, we reported a facile and scalable way to fabricate the lightweight and strong microcellular polypropylene/talcum (PP/talc) component. Both PP/talc microcomposite and PP/talc nanocomposite were prepared by the twin-screw compounding, and the SEM images show a uniform dispersion of talc. The DSC analysis results demonstrate that either the micro or nano talc is very effective in promoting the crystallization of PP. The rheological tests show that both the micro talc and the nano talc lead to obviously enhanced viscoelastic properties of the PP melt, while the effect of the nano talc is much more pronounced than that of the micro talc. Thanks to the enhanced crystallization and improved viscoelastic behavior, both the microcomposite foam and the nanocomposite foam shows much refined cellular structure than the pure PP foam. The PP/talc microcomposite foam shows significantly improved strength but seriously deteriorated toughness, compared with the pure PP foam. In contrast, the PP/talc nanocomposite foam shows simultaneously improved strength, rigidity and toughness. Notably, the tensile toughness and the Gardner impact toughness of the PP/talc nanocomposite foam are dramatically enhanced by 226.1% and 166.2%, respectively. Taking into account the flexible and scalable features of the processing methodology, the lightweight and strong PP/talc nanocomposite foam shows a promising future to replace the solid structural components in many industrial applications such as automotive and consumer electronics.

Flexural properties and morphology of microcellular-insert injection molded all-polypropylene composite foams

Single-polymer composite foams or all-polymer composite foams have been developed with further reduced weight, good interfacial adhesion and enhanced recyclability. All-polypropylene (PP) composite foams were prepared by the insert injection molding combined with microcellular injection molding. Flexural properties of the all-PP composite foams were reported and compared with solid PP, all-PP composites and PP foams. In comparison with solid PP, the 4.23% weight reduction, 16.52% increase of flexural strength and 20% increase of flexural modulus were achieved by the all-PP composite foams produced at the injection temperature of 220 °C and injection speed of 40 mm/s. Especially, the all-PP composite foams could have lower weight but higher flexural strength than the all-PP composites without foaming. The effect of injection temperature and injection speed on the flexural properties of all-PP composite foams was investigated to explore the optimum processing parameters for balancing good interfacial adhesion and weight reduction. Morphology properties were also investigated. The effect of processing conditions on the cell size and cell density of the all-PP composite foams was analyzed.

Evolution of double crystal melting peak in polypropylene foam assisted by β‐nucleating agent and supercritical CO2

ABSTRACTPolypropylene (PP) foams with double crystal melting peak structure were prepared using supercritical CO2 as blowing agent. Such structure was induced by the β‐nucleating agent (NA) and dissolved CO2 in a lab‐scale autoclave system. From the dynamic rheological behaviors, one can see that long chain branching polypropylene (LCBPP) possess better melt elasticity than linear polypropylene (LPP). In order to improve the foamability, LPP was blended with LCBPP. The results of differential scanning calorimeter and wide‐angle X‐ray diffraction indicated that NA was helpful for the introduction of β‐crystal in LPP, but not for LCBPP and PP blends. Therefore, the foamability and the content of β‐crystal of various PP foams can be effectively controlled by adjusting the ratio of LPP and LCBPP. Meanwhile, both the cooling rate and the content of NA affected the formation of β‐crystal in various PP samples. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46007.

Effects of compatibility on foaming behavior of polypropylene/polyolefin elastomer blends prepared using a chemical blowing agent

ABSTRACTPolypropylene (PP) exhibits poor foaming property because of its low melt strength arising from its linear chains and relatively narrow molecular weight distribution. To fabricate a PP foam without crosslinking, PP should be blended with polyolefin elastomers (POEs) using chemical blowing agents. In this study, the effects of POE types and contents in a PP matrix were studied by analyzing the melt flow index, morphology, and thermal and dynamic viscoelastic properties. Furthermore, the POE type/content and foaming conditions (i.e., foaming temperature and oven residence time) were optimized by investigating the volume expansion ratio (VER), cross‐sectional morphology, and hardness of the PP/POE foams. We focused on how the foaming behavior and foaming conditions were affected by the compatibility and POE content in the PP/POE blend. The results demonstrated that the optimal VER of ∼9 was obtained at 30 wt % POE and foaming conditions of 220 °C for 9 min. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45201.

Effects of hydrophobic-modified cellulose nanofibers (CNFs) on cell morphology and mechanical properties of high void fraction polypropylene nanocomposite foams

Nanocomposite foams based on isotactic polypropylene (iPP) and cellulose nanofibers (CNFs) with a void fraction as high as 80% were fabricated by a core-back foam injection molding (FIM). The hydrophobic CNFs were modified using alkenyl succinic anhydride. Different rheological curves such as the complex viscosity and tan δ–ω curves were investigated to distinguish the effects of CNFs on PP’s viscoelastic properties. Fast scanning chip calorimetry (FSC) results revealed that the added CNFs significantly increased the crystallization temperature and accelerated the crystallization process. Consequently, CNFs, especially with a concentration between 1 and 5wt%, could clearly reduce PP’s cell size and increase its cell density. The specific flexural modulus and bending strength were increased when the void fraction was lower than 80%. These findings suggest that CNFs is effective for strengthening PP foams, and such materials exhibit great potential for automotive and construction applications.

Influence of molecular structure on the foamability of polypropylene: Linear and extensional rheological fingerprint

The foaming structure and rheological properties of four different isotactic homo-polypropylenes with various molecular weights and an isotactic long chain branched polypropylene were investigated to find a suitable rheological fingerprint for PP foams. The molecular weight distribution and thermal properties were measured using GPC-MALLS and differential scanning calorimetry, respectively. Small amplitude oscillatory shear data and uniaxial extensional experiments were analyzed using the frameworks of van Gurp-Palmen plot (δ vs. | G*|) and the molecular stress function model, respectively. These analyses were used to find a correlation between the molecular structure, rheological properties and foaming structures of linear and long chain branching polypropylenes. Two linear viscoelastic characteristics, | G*| at δ = 60° and | η*| at ω = 5 rad/s were used as criteria for foamability of these polymers, where decreasing of both parameters by increasing the long chain branching content results in smaller cell size and higher cell density. The molecular stress function model was able to quantify the strain hardening properties of long chain branching blends using small amplitude oscillatory shear data and two nonlinear material parameters, 1 ≤ β ≤ 2.2 and 1 ≤ [Formula: see text] ≤ 600, where the minimum and maximum values of these parameters belong to the linear and long chain branched polypropylene, respectively. Increasing the long chain branched polypropylene content of the PP blends increased strain hardening, and therefore improved the foaming characteristics significantly by suppressing the coalescence of cells. Dilution of linear PP with only 10 wt% of long chain branched polypropylene enhanced the cell density from 5.7 × 106 to 2.7 × 107 cell/cm3 and reduced the average cell diameter from 58 to 26 µm, respectively, while their volume expansion ratio remained in the same range of 2–3. Increasing of long chain branching to 50 and 100 wt% enhanced the V.E.R. to 6.2 and 7.8, respectively.

Open‐cell polypropylene/polyolefin elastomer blend foams fabricated for reusable oil‐sorption materials

ABSTRACTThe fabrication of high‐performance oil sorbents is of great significance for oil spill cleanup. The main objective of this study was to prepare open‐cell polypropylene/polyolefin elastomer (PP/POE) blend foams for fabrication of reusable sorbents for oil sorption. Open‐cell PP/POE blend foams were prepared via continuous‐extrusion foaming using supercritical carbon dioxide as the blowing agent. The interconnected open‐cell structure was characterized by scanning electron microscopy. The hydrophobicity and lipophilicity of PP/POE open‐cell foams were revealed by tests of contact‐angle measurement, water and cyclohexane sorption on the foam surface, CCl4 and cyclohexane sorption in water, and oil/water separation. Further, the sorption tests indicated that PP/POE blend foams showed larger oil‐uptake capacities than pure PP foams. In addition, cyclic compression tests showed that PP/POE open‐cell foams had excellent ductility and significantly improved recoverability compared to pure PP foams. In cyclic sorption–desorption tests, the sorption kinetics was studied in terms of capacity and saturation time, showing that PP/POE foams kept larger sorption capacities for 10 cycles, with larger sorption rates and good reusability. Based on the high open‐cell content, the good hydrophobic and oleophilic properties, the high oil‐sorption capacity, the improved recoverability, the large sorption rate, and the good reusability in cyclic oil‐sorption performance, the PP/POE open‐cell foams have shown promise as potential oil sorbents in applications for oil spill cleanup. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43812.

Supercritical CO2 foaming of pressure-induced-flow processed linear polypropylene

Linear polypropylene is very difficult to foam due to its low melt strength and high crystallinity. Pressure-induced flow (PIF) has been demonstrated to be able to improve the foamability of linear PP under a very high pressure. In this study, we report a systematic evaluation to optimize PP foaming process using supercritical CO2. PP was firstly processed by means of PIF at optimized conditions. For CO2 foaming of PP, the effect of foaming pressure and saturation time was investigated in detail. A threshold foaming pressure of 13.8MPa was found to be needed to achieve low-density foams. Comparing to commercially available EPP and high melt strength PP foams, the PIF PP foams possess much higher compressive strength and thermal stability at lower densities.