Blend Foams Research Articles

Fabrication of lightweight microcellular foams in injection-molded polypropylene using the synergy of long-chain branches and crystal nucleating agents

Herein, we have fabricated microcellular injection-molded foams by combining long-chain branched polypropylene (LCBPP) and 1,3:2,4 bis-O-(4-methylbenzylidene)-D-sorbitol gelling agent (MD) using a core-back foam injection molding (FIM) technique. Microcellular foams of LCBPP/MD blends having an average cell diameter of approximately 2.5 μm and a cell density on the order of 1010 cells/cm3 were achieved with a void fraction of 50%. Fast scanning chip calorimetry results revealed that the added MD acted as effective nucleating agents and promoted crystallization for the LCBPP. Interestingly, the development of microcellular foams led to notable advances in tensile toughness from 44.1 MJ/m3/(g·cm−3) and 111% of neat LCBPP foams to 172.1 MJ/m3/(g·cm−3) and 440% of LCBPP/MD blend foams in terms of specific breaking energy and elongation at break, respectively. These results revealed that the lightweight microcellular PP with improved toughness could be developed using FIM, which offers a viable approach to fabricate injection-molded products for large-scale applications.

Poly(Lactic Acid)-Polybutylene Succinate-Activated Carbon Composite Foams

Polymer blends of poly (lactic acid) (PLA) and polybutylene succinate (PBS) containing activated carbon (AC) were foamed by using Azodicarbonamide (ADC) through an extrusion process. The composite foams containing 5 phr of AC had lower density than those without AC loading for PLA:PBS ratios of 90:10, 80:20, 70:30, and 60:40. The incident of higher void fraction was the consequences of more foaming nucleation centers which were induced by adding AC in the composite foam. Maximum reduction of density by 50% with the void fraction of 50% was achieved when both ADC and AC were applied at 5 phr with the PLA:PBS ratio of 80:20. The addition of AC in composite foams enhanced the crystallization in PBS phase but had no effects on PLA crystallinity. The thermal stability of composite foams with and without AC dosages for each PLA:PBS proportion was slightly changed. For PLA-PBS blend foams, the more PLA loading there was the more tensile strength and modulus there would be. For PLA-PBS-AC composite foams, AC could improve the modulus and tensile strength of composite foams in PBS-rich samples whereas no effect on PLA-rich samples.

Physicomechanical, friction, and abrasion properties of EVA/PU blend foams foamed by supercritical nitrogen

Elastomer foams based on EVA, PU, and EVA/PU blends formulated for shoe‐sole applications were prepared by a supercritical N2 batch foaming process and characterized for physicomechanical, friction and abrasion properties. The blending of EVA with PU was aimed for improving the friction and wear characteristics of the EVA based foams. All of the foams prepared showed spherical cells with closed‐cell morphology and the cell sizes varied with varying the EVA/PU blend ratio and CaCO3 content of the foams. The properties such as hardness and resilience, friction coefficients and abrasion resistance improved for the EVA/PU blend foams compared to the EVA foam, but their compression set, tensile strength, and tear strength were inferior to the EVA foam. The incorporation of CaCO3 filler increased density, hardness, tensile strength, and tear strength of the EVA/PU blend foams but decreased resilience, compression set, friction coefficients, and abrasion resistance. The improvement in friction coefficients and wear resistance obtained in the EVA/PU blend foams was significant for shoe‐sole applications. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

Effect of ENR Contents on Cure Characteristic and Properties of NR/ENR/EVA Foam

This research studied foaming of natural rubber (NR), epoxidized natural rubber (ENR) and ethylene vinyl acetate copolymer (EVA) blends vulcanizate. The contents of NR/ENR/EVA investigated were 60/10/30, 70/10/20, 50/20/30 and 60/20/20 to keep NR based to 70 and 80 % by weight whereas EVA contents were 20 and 30 % by weight. ENR used in this research was ENR 50. The content of ENR was varied as 10 and 20 % by weight with restpect to total polymer content. The Efficient vulcanization and peroxide systems were used for rubber vulcanization in order to cure both rubber and EVA. Oxydibenzenesulfonyl hydrazide (EW or OBSH) was used as foaming agent. The results showed that rubber blends with 20% ENR tended to show better compatibilization between NR and EVA. The viscosity of rubber blend which indicated by minumum torque was increased with the content of ENR. Cell size of rubber blends foam containing ENR 20 % showed rather normal distribution than ENR 10%. Foam with high content of NR based rubber showed slightly higher density than the other systems. Tensile properties of rubber blends foam were dependent upon NR based contents and compatibility between NR and EVA. Rubber blends foam with high ENR content showed higher specific secant modulus. The specific tensile strength and elongation at break were slightly inferior. The specific tear resistance of the rubber foam was independent on compatibility. High EVA content reduced both specific compressive modulus and compressive strength of the foam. For the foam that contained EVA domain showed permanent deformation and hence high in compression set. Compatibilized rubber blend foams and the foam with high EVA possessed low ball rebound resilience.

Processing and properties of an ethylene–vinyl acetate blend foam incorporating ethylene–vinyl acetate and polyurethane waste foams

ABSTRACTWaste polyurethane foam (w‐PU) and waste ethylene–vinyl acetate foam (w‐EVA) were used as fillers for the production of an ethylene–vinyl acetate (EVA) blend foam. Two different foaming techniques (single‐stage and heat–chill processes) were used for this purpose. The waste foam concentration was varied up to 30 wt % of the original EVA. The physical, mechanical, and morphological properties of the filled foam were studied. The single‐stage process produced blend foams with a lower density and a greater cell size than the foams obtained by the heat–chill process. The density and compression strength of the blend foam increased as the percentage of w‐PU foam increased. However, for the w‐EVA/EVA blend foams, the addition of w‐EVA foam did not significantly affect the density or compression strength compared to the original EVA foams. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44708.

Enhancing the Melt Strength of Poly(Lactic Acid) via Micro-Crosslinking and Blending with Poly(Butylene Adipate-co-Butylene Terephthalate)for the Preparation of Foams

The melt strength of poly(lactic acid) (PLA) is an important factor in preparing foams and blowing films. Aiming to endow PLA with a suitable melt strength via a slight crosslink, a superficial micro-crosslinking method was introduced in which the PLA feed was mixed with benzoyl peroxide (BPO) and crosslinked in a 100 °C oven for 1 h. Additionally, poly(butyleneadipate-co-terephthalate) (PBAT) was blended with the crosslinked PLA (C-PLA) to further improve melt strength and viscosity. The blend foams were prepared using a single-screw extruder and azodicarbonamide as a foaming agent. The properties were characterized by gel fraction, melt flow rate (MFR), rheometry, DSC and SEM. The rheological results showed that the complex viscosity and storage modulus of C-PLA and C-PLA/PBAT blends increased, attributed to the micro-crosslinking and addition of PBAT and indicating an improvement in melt strength. Furthermore, the crystallization of modified PLA was also enhanced. Compared with pure PLA foams, the C-PLA/PBAT blend foams showed larger cells with more uniform shapes and homogenous distribution. This approach to improve the melt strength of polymers with micro-crosslinking and blending with PBAT represents an attractive method for preparing foams with regular cells.

Microstructure, physical, and mechanical properties of LDPE/UHMWPE blend foams

An investigation was reported on the effect of foaming parameters on the microstructure, mechanical properties, and thermal conductivity of low-density polyethylene (LDPE) foams containing various amount of ultrahigh-molecular-weight-polyethylene (UHMWPE) as a reducer of chemical cross-linking. Azodicarbonamide (ADCA) and dicumyl peroxide (DCP) were used as foaming agent and cross-linking agent, respectively. The LDPE/UHMWPE blends were prepared in an internal mixer and foamed using a single-stage compression molding technique. Considering various parameters and their levels, optimization of Taguchi experimental design was carried out, an L9 orthogonal standard array was selected and the efficient levels for different variables were calculated using analysis of variance (ANOVA) of the results. Also due to different objective functions investigated in this process, optimization of overall evaluation criteria (OEC) method was used. The results revealed that addition of UHMWPE leads to a significant increase in the storage modulus and complex viscosity of melt as well as a considerable decrease in gel content of blend foams compared to neat LDPE foam containing the same amount of DCP was observed. Also in presence of UHMWPE, the foam cell size was decreased compared to previous studies in the same condition. A linear relationship between relative density and thermal conductivity as well as cell size and thermal conductivity was observed. ANOVA results revealed that foaming temperature is the most effective parameter on foam properties and OEC results suggested 10 phr ADCA, 0.6 phr DCP, foaming temperature of 180°C, and 4 min soak time at foaming temperature are the optimum levels of parameters.

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.

Hydrophobic modification of polypropylene/starch blend foams through tailoring cell diameter for oil-spill cleanup

PP/starch blend foams with good hydrophobicity and oil recovery efficiency were prepared by tailoring cell diameter without involving any chemicals.

Cell nucleation in dominating formation of bimodal cell structure in polypropylene/polystyrene blend foams prepared via continuous extrusion with supercritical CO2

It is generally difficult to predict the cell structure foamed from a binary polymer blend compared to a single polymer, as many factors in polymer blends add to the complexity of the foaming process without easy control, such as blend morphology, blend viscosity, and solubility and diffusivity of the foaming agent, etc. In this study, polypropylene (PP)/polystyrene (PS) blend foams with a bimodal cell structure were prepared by using supercritical carbon dioxide (scCO2) in continuous extrusion. By comparison of the cell structure of blend foams before and after extraction, it was found that the large cells were mainly formed in PS phase, while the small ones were mostly formed in PP phase. A possible mechanism was proposed to explain the formation of the bimodal cell structure. It was believed that a prominent difference in cell nucleation in the two phases of the PP/PS blends was required for the formation of bimodal cell structure. The proposed mechanism was confirmed by further experimental results, which showed that the bimodal cell structure could be changed by altering the nucleation ability in PP phase and PS phase through changing experimental conditions, such as the content of scCO2 and the pressure drop, or through applying a heterogeneous nucleating agent.

Facile Preparation of Open‐Cell PP/TPS Blend Foams Using Water as a Blowing Agent

Extrusion foaming using water as a blowing agent offers a green process of preparing polymer foams. Due to the low water solubility of hydrophobic polymers such as polypropylene (PP), it is difficult to produce low‐density foams of such pure polymers. In this study, starch was utilized as an effective water carrier and open‐cell PP/thermoplastic starch (TPS) blend foams with apparent density as low as 19.5 kg · m−3 and open‐cell content of 95.6% were successfully prepared. A possible expansion mechanism is also proposed to better understand the observed foaming behavior. The PP/TPS blend foams with low density and high open‐cell content are found to be a promising candidate absorbent material for oil spill cleanup application.

Foaming behavior of bio‐based blends based on thermoplastic gelatin and poly(butylene succinate)

ABSTRACTBiodegradable thermoplastic gelatin/poly(butylene succinate) (TPG/PBS) foams were prepared by melt mixing and subsequent batch foaming with supercritical CO2. Shear viscosity and calorimetric properties of the various blends were investigated using a rotational rheometer and a differential scanning calorimeter, respectively. TPG/PBS blends show poor miscibility at all blend ratios. The addition of PBS reduced the melt viscosity and increased both the CO2 diffusivity and the thermal stability of TPG. Results from foaming experiments show that the blend foams exhibit smaller cell size and higher cell density compared to the neat TPG foam due to the lower melt viscosity and to their lower gas barrier. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42704.

Influence of polyamide–imide concentration on the cellular structure and thermo-mechanical properties of polyetherimide/polyamide–imide blend foams

The present work considers the preparation of medium-density polyetherimide (PEI)/polyamide–imide (PAI) blend foams by means of water vapor-induced phase separation (WVIPS) and their characterization. While pure polymer foams showed homogeneous cellular structures with average cell sizes of 10–12μm, PEI/PAI blend foams presented two distinctive closed-cell structures depending on the composition of the blend. At the lowest concentration of PAI (25wt%) foams showed a very fine homogeneous microcellular structure with an average cell size of 1.4μm, consequence of good miscibility between both polymers, while at the highest studied concentration of PAI (50wt%) foams presented a dual cellular structure formed by small cells (around 1μm in size) within the walls of considerably bigger ones (22μm in size) due to polymer phase separation. The blend foams presented a thermal decomposition behavior similar to that of pure unfoamed polymers, with the foam with 25wt% PAI showing a slightly higher thermal stability. Furthermore, this particular foam presented an improved specific storage modulus compared to pure PEI foam and to the one with 50wt% PAI. X-ray diffraction (XRD) analysis indicated that no polymer crystallization was induced by foaming.

Thermal Properties and Cellular Structure of Cornstarch-Based Foams Formed by Extrusion Technology

The aim of this work was to investigate the edible corn grit/PVOH (polyvinyl alcohol) blends of their thermal properties by using differential scanning calorimetry (DSC) and thermogravimetric analysis, and the average pore sizes and cellular structures of the blend foams were also characterized by using scanning electron microscopy. The thermal decomposition of edible corn grit/PVOH blends shifted slightly toward lower temperature compared to PVOH. This result shows that edible corn grit/PVOH blends suppress the thermal stability of PVOH. DSC result shows that PVOH and edible corn grits were miscible. Furthermore, the cell sizes become smaller and more uniform and the cell walls become thinner with the increase in PVOH ratio. Moreover, using the CaCO3 also made the cell sizes become smaller and more uniform. Corn-based foams have practical mechanical properties, but they are difficult to mold into shaped products. They will have a greater commercial potential if the extrusion process were more amenable to making molded foam articles, such as food and beverage containers, and if it were compatible with fiber or other reinforcing materials. Practical Applications In this study, edible corn grit/PVOH blends were prepared by using extrusion technology and the CaCO3 as the thermal conductor. Corn grit is renewable from carbon dioxide, water and sunshine. It is biodegradable, cheap and easily modified physically or chemically. This means someday it is unnecessary to rely on petroleum to prepare polymers; people may “plant” polymers of suitable performances from the earth, and the environmental problems will no longer be as severe as today. At present and in the near future, different physical and chemical approaches are effective strategies to develop completely starch-based biodegradable polymers of appropriate biocompatibility, degradation rate and physical properties for various applications.

Design and characterization of biocompatible shape memory polymer (SMP) blend foams with a dynamic porous structure

This study presents a comprehensive morphological, physical, and shape memory characterization of biocompatible shape memory polymer (SMP) blend foams composed of thermoplastic polyurethane (TPU) and polylactic acid (PLA). The TPU/PLA blend compositions studied were 80/20, 65/35, and 50/50 in weight percentage. The influence of blend composition and processing conditions on the pore morphology of the foams were studied with the scanning electron microscope (SEM). The results showed that all the TPU/PLA compositions formed close-celled porous structures. A number of physical characteristics of the foams were characterized, including relative density, pore density, porosity, and average pore size. The shape memory properties of the porous structure formed in the foams were investigated. The 80/20 and 50/50 TPU/PLA blends, and neat TPU contained a dynamic porous structure that contracted uniformly upon shape recovery. The recovery of the pores in the neat TPU was captured with a CCD camera in real time and the recovery force of the 80/20 TPU/PLA blend was measured with a custom built force sensor. These shape memory polymer foams are currently under investigation for biomedical applications, such as gastro-retentive drug delivery systems and wound dressings.

Preparation of native cassava starch and cross‐linked starch blended foams

Starch foams from native cassava starch/cross‐linked starch blends were prepared by baking in a hot mold. The native cassava starch/cross‐linked starch ratio was varied in the series of 100/0, 80/20, 60/40, 50/50, 40/60, 20/80, and 0/100. The effect of the native cassava starch/cross‐linked starch ratio on the properties of foams including density, morphology, water adsorption, impact strength, and thermal stability was investigated. The blending of cross‐linked starch resulted in a higher density of the foams. The impact strength of the blend foams were between 232 and 268 J/m2. The adsorption of water by the modified starch (7.3%) and the blend foams (11–12%) was lower than for the native cassava starch foam (13.9%). The size of the cells in the blend starch foam was between the cell size of the native cassava starch and the cross‐linked starch foams.

Open-cell foams of polyethylene terephthalate/bisphenol a polycarbonate blend

Open microcellular foams of polyethylene terephthalate (PET)/polycarbonate (PC) blends were prepared by controlling their foaming behavior at the interface between these two polymers. Interface modification was a crucial factor in governing the foaming behavior and cell morphology of the blend foams: annealing at 280°C, i.e., conducting the transesterification reaction, generates a PET-b-PC copolymer, which lowers the interfacial tension, increases the affinity between PET and PC, and decreases the crystallinity of the PET domains. When CO2 foaming was performed at the interface modified with the copolymer, an interesting fibril-like structure was formed. The cell density of the PET/PC blend then increased, and its cell size reduced to the microscale while maintaining a high open-cell ratio. The effect of heat annealing (transesterification reaction) on CO2-foaming was studied to reveal the relationship among the interface affinity, crystallinity, and degree of fibrillation. The optimal heat-annealing procedure generated a fibril-like structure in the PET/PC blend foams with a high cell density (7 × 1011 cm−3), small cell size (less than 2 μm), and 100% open-cell ratio. POLYM. ENG. SCI., 55:375–385, 2015. © 2014 Society of Plastics Engineers

Influence of polyethylene disperse domain on cell morphology of polystyrene-based blend foams

To gain insight into the foamability of polystyrene-based polymer blends containing different types of polyethylene close to the experimental boundary conditions of temperature, batch pressure quench foaming experiments were conducted using CO2 as a physical foaming agent. The blends were prepared by melt-mixing in a twin screw extruder and then physically foamed by depressurizing CO2 from 10 MPa in an autoclave at various foaming temperatures in the range of 90–140℃. At low temperatures, where viscosity of polyethylene (PE) was lower than that of PS, microcellular foams with bubble sizes of approx. 100 µm in diameter were obtained, and the dispersed PE enhanced bubble nucleation. It was also found that the expandability of bubbles was correlated with complex viscosity PE. At the highest foaming temperature, where the viscosity of PE became lower than that of the matrix, the dispersed PE worked as a cell opening agent.

PP/PS/PMMA Ternary Blend Foaming Using Supercritical CO<sub>2</sub>

The aim of this work is to study controllability of cell structure of foam by a Polypropylene (PP)/Polystyrene (PS)/ Polymethyl methacrylate (PMMA) ternary polymer blend. The effects of different polymer matrix, its blend morphology, and rheology on the cell structure of the ternary blend foam were investigated. The batch pressure quenched foaming of the ternary blend with supercritical carbon dioxide (CO2) was conducted in the temperature range from 60 to 160°C for PP matrix and 60 to 140°C for PS and PMMA matrices to observe the controllability of bubble location and size. The experimental results showed that interfacial tension, foaming temperature, and viscoelasticity are the important factors to control the cellular structure in ternary blend system.

Plasticization of [C12MIM][PF6] Ionic Liquid on Foaming Performance of Poly(methyl methacrylate) in Supercritical CO2

A series of poly(methyl methacrylate) (PMMA)/1-dodecyl-3-methylimidazolium hexafluorophosphate ionic liquid ([C12MIM][PF6]) blends were prepared by melt blending. The compatibility of blends was verified by scanning electron microscopy and differential scanning calorimetry. The introduction of [C12MIM][PF6] decreased the glass transition temperature of the blends due to its plasticization effect and increased the diffusivity of CO2 without significantly affecting the CO2 solubility. These blends were foamed with supercritical CO2 as the blowing agent via a pressure-quenching process. The foaming conditions are divided into three regions according to the main morphological difference of foams. At relatively low temperatures and pressures, neat PMMA could not be foamed, while the addition of [C12MIM][PF6] facilitated the formation of cells. By increasing temperature or pressure, neat PMMA foams were obtained with wide cell size distribution, while the blend foams were formed with narrowed cell size distribution and increased cell size. At high temperatures and pressures, neat PMMA was foamed with narrow cell size distribution and high cell density, while the major effect of [C12MIM][PF6] was to increase the cell size. These results indicated that the plasticization effect and the low surface energy of [C12MIM][PF6] accounted for the differences on the cell morphology between neat PMMA and the blend foams.