Blend Foams Research Articles

Influence of Ethylene Plasma Treatment of Agave Fiber on the Cellular Morphology and Compressive Properties of Low-Density Polyethylene/Ethylene Vinyl Acetate Copolymer/Agave Fiber Composite Foams

Agave fibers (AF) were incorporated either pristine (AFp) or surface treated by ethylene plasma (AFm) in low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) blends at a ratio of 1 : 1 and foamed by chemical means. The role of the AF content (3, 6, 9, 12, and 15 wt.%) and its surface modification on the cellular morphology and mechanical properties of LDPE/EVA/AF foams under compression is investigated herein. Fourier transform-infrared spectroscopy, contact angle, and water suspension of AF suggest that plasma treatment using ethylene successfully modifies the surface nature of AF from hydrophilic to hydrophobic. AF and the surface treatment have an important role on the morphological properties of the foams. Composite foams reinforced with 12 wt.% AFm exhibited the highest mechanical properties improvements. At this fiber content, the composite foams enhanced 30% of the compressive modulus and 23% of the energy absorption under compression with respect to the neat polymer blend foam, as a result to the formation of more uniform cells with smaller size and the enhancement of compatibility and spatial distribution of the AFm in the polymer composite foams due to thin clusters of polyethylene-like polymer deposited on the AF surface.

Development and characterization of a poly (vinyl alcohol) and sodium alginate blend foam for wound dressing loaded with propolis and all‐trans retinoic acid

AbstractPropolis is a complex mixture of phytochemicals, with antibacterial, anti‐inflammatory, and healing properties. All‐trans retinoic acid is implicated in wound healing by stimulating angiogenesis, cell recruitment, extracellular matrix deposition, and reepithelization. The incorporation of both agents to a polymeric wound dressing composed of poly (vinyl alcohol) and sodium alginate may result in improved healing allied to controlled release, fluid uptake, and wound protection. In the present work, we have physically characterized this wound dressing and analyzed its release kinetics. The anti‐inflammatory capacity was assayed. SEM images showed a highly porous structure with a diverse morphology. FTIR spectra displayed a highly cross‐linked structure with both polymers connected by hydrogen bonds and acetal bridges. The wound dressings were able to retain great volumes of PBS. Propolis and vitamin A releasing behavior were maintained for 6 h. The concentrations of the biologically active substances were capable of promoting anti‐inflammatory action in an erythrocyte membrane stabilization model. The wound dressings obtained here showed adequate physical properties. The fabrication process did not affect the anti‐inflammatory capacity. Further tests are needed to ensure the biocompatibility and to assess other biological activities of the therapeutic agents.

Study on microcrystalline cellulose/chitosan blend foam gel material

Abstract In the present contribution, an environmental-friendly and cost-effective adsorbent was reported for soil treatment and desertification control. A novel foam gel material was synthesized here by the physical foaming in the absence of catalyst. By adopting modified microcrystalline cellulose and chitosan as raw materials and sodium dodecyl sulfonate (SDS) as foaming agent, a microcrystalline cellulose/chitosan blend foam gel was synthesized. It is expected to replace polymers derived from petroleum for agricultural applications. In addition, a systematical study was conducted on the adsorbability, water holding capacity and re-expansion performance of foam gel in deionized water and brine under different SDS concentrations (2%–5%) as well as adsorption time. To be specific, the adsorption capacity of foam gel was up to 105g/g in distilled water and 54g/g in brine, indicating a high water absorption performance. As revealed from the results of Fourier transform infrared spectroscopy (FTIR) analysis, both the amino group of chitosan and the aldehyde group modified by cellulose were involved. According to the results of Scanning electron microscope (SEM) analysis, the foam gel was found to exhibit an interconnected pore network with uniform pore space. As suggested by Bet analysis, the macroporous structure was formed in the sample, and the pore size ranged from 0 to 170nm. The mentioned findings demonstrated that the foam gel material of this study refers to a potential environmental absorbent to improve soil and desert environments. It can act as a powerful alternative to conventional petroleum derived polymers.

Morphological, thermal, and thermomechanical properties of cellulose nanocrystals reinforced polylactide/poly [(butylene succinate)-co-adipate] blend composite foams

This study examines the influence of cellulose nanocrystal (CN) particles on the morphological, thermal, and thermo-mechanical properties of polylactide (PLA)/poly [(butylene succinate)-co-adipate] (PBSA) blend foams prepared by casting and particulate leaching method using fructose as porogen particles. The morphological analysis showed an interconnected open-cell structure, with porosity above 80%. The crystallinity of the prepared foams was disrupted by the inclusion of CN particles as observed from XRD analyses, which showed a decrease in PLA crystal peak intensity. With regards to neat blend foam, the onset thermal degradation increased with the addition of CN particles, which also increased the thermal stability at 50% weight loss. Furthermore, CN acted as a reinforcing agent in improving the stiffness of the prepared blend foam. Overall, completely environmentally friendly foams were successfully prepared, as a potential material that can replace the current existing foam materials that pose many environmental concerns. However, there is a need to develop an environmentally friendly processing technique.

Influence of Azodicarbonamide on Physical and Mechanical Behaviours of Thermoplastic Blend

Foaming technology is promising in producing foamed materials which can offer benefits such as lowering the cost and weight of materials as well as their utility in many applications. In this study, the thermoplastic blend of recycled high density polyethylene and recycled polyethylene terephthalate was foamed with azodicarbonamide chemical foaming agent (CFA) at 0.5-2.0 phr. The blending of thermoplastic was carried out via extrusion and the foaming process occurred during hot/cold pressing. The cell morphology, density and mechanical properties were examined. Field emission scanning electron microscope (FESEM) micrograph showed that the thermoplastic blend foamed with 1.5 phr CFA had the cellular morphology structure with non-collapsed cells and better cell distribution. As the CFA content increased, the density of blend foams decreased accordingly. The minimum density was achieved at 1.00 g/cm3 for 2.0 phr ADC. Tensile and bending properties generally decreased with the content of CFA added. The impact strength of blend foams increased when the CFA added up to 1.0 phr and then reduced with further CFA content. It can be concluded that the fabricated foamed blend can give value added to the recycled polymers.

Structure, physical properties, and flame retardancy of POE/NR/EG blend foams: Effect of crosslinking

Elastomeric foams were produced by melt-mixing of polyethylene-octene elastomer (POE), natural rubber (NR), and expandable graphite (EG) in an internal mixer. The blend was later foamed by compression-molding method. EG was used as a filler to enhance flame retardancy of the blend foams. Dicumyl peroxide (DCP) was used as curative to crosslink the blend foams. The influence of DCP content (0.5, 0.7, 0.9, and 1.0 part(s) by weight, pbw) on rheological properties, structure, density, mechanical properties, thermal conductivity, and flame retardancy of the POE/NR/EG blend foams was investigated. The rheological analysis showed that the melt strength/viscosity of the POE/NR/EG blend foams increased with more DCP addition due to promoted crosslinking in the blend foams. The cellular structural observation by SEM technique revealed that the POE/NR/EG blend foams had close-cell structure. Increasing DCP content, the blend foams had smaller cell and narrower cell size distribution. The degree of porosity, however, was highest for the foamed blends added with 0.7 pbw DCP, which brought about the lowest thermal conductivity. Furthermore, it was found that the density, tensile strength, elastomeric recovery, and compressive strength increased with increasing content of DCP, but the elongation at break decreased. The POE/NR/EG blend foams reached the horizontal burning level of HF-1, and their oxygen index increased in accordance with an increase of DCP content. The results indicated that an appropriate use of DCP was critical for the crosslinked POE/NR/EG blend foams with optimum cellular structure, providing the best improvement in thermal insulation properties and good flame retardancy.

Foaming and Physical Properties, Flame Retardancy, and Combustibility of Polyethylene Octene Foams Modified by Natural Rubber and Expandable Graphite

Flame‐retardant blends of polyethylene‐octene elastomer (POE) and natural rubber (NR) filled with expandable graphite (EG) were melt‐mixed with azodicarbonamide to prepare elastomeric foams. The effect of the NR incorporation on the properties of EG filled POE foam was investigated. Gel content and microstructure observations revealed that the addition of NR into the POE/EG blend induced change in molecular structure, which produced a finer cellular structure during foaming. The compressive strength and elastomeric recovery of the POE/NR/EG blend foams were found to increase with increasing NR content. Based on the limiting oxygen index and horizontal burning measurements, all the POE/NR/EG blend foams were found to have good flame‐retardant properties. On the other hand, these POE/NR/EG blend foams exhibited higher combustion rates with an increasing NR content under high heat radiation and temperature in a cone calorimeter test. This study demonstrates that the combined use of NR as a modifier and EG as a flame retardant in POE foams provides an effective and practical method of obtaining well‐balanced improvements in cellular structure, mechanical properties, and flame resistance.

Preparation and properties of ethylene-vinyl acetate copolymer-based blend foams

In this study, ethylene-vinyl acetate (EVA) copolymer-based blend foams with polyolefin elastomers (POEs), low-density polyethylene, or styrenic thermoplastic elastomers were prepared as a potential resilient material for reducing inter-floor noise. Various properties of EVA blend foams were measured in order to reveal the effects of EVA content and types of pair polymers consisting of EVA blend foams on dynamic stiffness, which is one of the key factors of resilient materials, in relation to hardness, specific gravity, and resilience. These properties had not been introduced by the construction industry until now. When the EVA/POE ratio was 20/80 and the foaming ratio was 210%, dynamic stiffness presented the lowest value at 5.97 MN m− 3. However, when the resilience was <20%, dynamic stiffness was as high as 37.66 MN m− 3 at an expansion ratio of 210% even when the specific gravity was low.

Micro/nanocellular polyprolene/trans‐1,4‐polyisomprene (PP/TPI) blend foams by using supercritical nitrogen as blowing agent

Toughed polypropylene (PP) foams, with the combination of blending with trans‐1,4‐polyisoprene (TPI) and micro/nanocellular structure in the matrix, were prepared using a batch foaming process and N2 as the blowing agent. The incorporation of TPI in the PP matrix induces the enhanced formability and the slightly improved ductility and toughness compared to the neat PP. The simultaneous existence of the TPI phase and micro/nanocellular structure makes the fracture behavior follow the shear yielding of a bundle of fibrils in the tensile load direction. The results of mechanical properties measurements show that the notched Izod impact strengths of foamed PP/TPI blend are two to three times larger than those of the unfoamed counterparts. The PP/TPI blend foam with 5phr TPI content shows the highest impact strength when the foaming temperature is 140°C, which is fivefold increase over that of the neat PP. The enhanced ductility and toughness of PP/TPI foams were found with the increasing foaming temperature. The insert of micro−/nanocellular in PP/TPI blends simultaneously makes the notched impact strength increase significantly, tensile strength decrease, and elongation at break increase obviously, which provides the possibility to combine the higher impact strength and toughness with the advantage of microcellular foaming. POLYM. ENG. SCI., 60:211–217, 2020. © 2019 Society of Plastics Engineers

Foaming properties of total zein, total kafirin and pre-gelatinized maize starch blends at alkaline pH

The effect of 0.1 M NaOH as a solvent and blending with pre-gelatinized maize starch on the foaming properties of laboratory extracted total zein and total kafirin were determined. Both total zein and total kafirin in 0.1 M NaOH were found to have higher foaming capacity (up to 118% foam volume increase) compared to their non-foaming (0% foam volume increase) properties in water. Blending with pre-gelatinized maize starch reduced the foam volume but increased the foam stability to more than 24 h. Total zein and total zein-pre-gelatinized starch blends had relatively higher foaming capacity than total kafirin and total kafirin-pre-gelatinized starch blends probably because zein was more surface active (more negative zeta potential value) than kafirin. However, total zein and total zein-pre-gelatinized starch blend foams were less stable with time than total kafirin and total kafirin-pre-gelatinized starch blend foams. This is possible because total kafirin, having higher amount of cysteine, can have higher degree of cross linking than total zein to form stronger lamellae. The foam microstructure, bubble size and foam film thickness are related to the foaming capacity and foam stability. Larger bubble size corresponded with higher foaming capacity but smaller bubbles and thicker film lamellae corresponded with lower foaming capacity and improved stability. The improved foam formation of total zein and total kafirin in 0.1 M NaOH solution compared to water could be due to the higher degree of deamidation in 0.1 M NaOH, which in turn would make them more surface-active and could increase their solubility/dispersibility.

Foaming Behavior and Microcellular Morphologies of Incompatible SAN/CPE Blends with Supercritical Carbon Dioxide as a Physical Blowing Agent.

The foaming process and cellular morphologies of poly(styrene-co-acrylonitrile) (SAN)/chlorinated polyethylene (CPE) blends with supercritical carbon dioxide (scCO2) as a blowing agent were investigated in this study. As compared to pure SAN foam in the same batch, the foamed blends with various CPE elastomer content had smaller average pore size and larger cell density. This is probably related to the inhibition of bubble growth by elastomer, resulting in poor melt flowability and strong viscoelasticity, and the efficient bubble heterogeneous nucleation caused by numerous phase interfaces inside the incompletely compatible blend system. In addition, many tiny interconnected holes through the pore walls were formed to connect adjacent micropores in foamed blend samples. The formation mechanism of such interconnected pores is probably due to the fracture of stretched melt around the bubble from phase interfaces with weak interactions. These facts suggest an effective path to control pore size, cell density and even interconnected pores of blend foams depends on the compatibility of the blend system and difference in foamability of individual components in supercritical CO2.

TPU/PLA blend foams: Enhanced foamability, structural stability, and implications for shape memory foams

ABSTRACTA series of thermoplastic polyurethane (TPU)/poly(lactic acid) (PLA) blends are studied in terms of morphological, thermal, and rheological properties by scanning electron microscopy, differential scanning calorimetry, and rheometry. Using supercritical CO2 batch foaming, the foamability of the blends is systematically investigated. It is found that the 80/20 (wt %/wt %) TPU/PLA blend (TPU80%) shows vastly enhanced foamability over a wide range of foaming conditions to produce foams with a myriad of cellular morphology. The foamability enhancement results from the improved cell nucleation and growth, and the changes in the polymer microstructure. Compared to elastic TPU foams, the TPU80% retain their shapes 3.4 times better. Mechanism for the enhanced stability is proposed and verified using Kohlrausch–Williams–Watts model. The materials developed in the study and the mechanistic understanding of the shape fixation process may facilitate the advancement of elastomeric foams in conventional use as well as in novel shape memory applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47416.

Effect of carbon nanofiller dimension on synergistic EMI shielding network of epoxy/metal conductive foams

The synergistic conductive network was constructed by incorporation of 1D carbon nanotube (CNT) or 0D acetylene black (ACET) in epoxy/nickel-coated carbon fiber (EP/NCCF) blend foams, and the influence of carbon nanofiller dimension on the electromagnetic interference (EMI) shielding performance of polymer/metal conductive foams was systematically investigated. Adding ACET into EP/NCCF foams improved the EMI SE merely by the enhancement in the conductivity, while mixing 1D CNTs with NCCFs built a multiple scale carbon-metal shielding network in EP foams. Due to the remarkable synergistic effect of the microwaves reflection from NCCF network and microwaves absorption from CNT network, the carbon-metal network exhibited a strong microwave attenuation. The EP/NCCF/CNT foam with only 2.35 vol% hybrid fillers showed an EMI SE of 40.8 dB, which was twice that of the EP/NCCF/ACET foam. The construction of the carbon-metal synergistic network opens a new avenue to design and prepare highly efficient EMI shielding composites materials.

Fabrication of hydrophilic small diameter vascular foam scaffolds of poly(ε-caprolactone)/polylactic blend by sodium hydroxide solution

Small diameter (diameter < 6 mm) vascular scaffolds lead to increased hemodynamic disturbances and thrombogenic complications which challenged the material scientists. A compatible interface with applicable mechanical properties of scaffolds is the key issue. In this study, 4 mm inner-diameter poly(ε-caprolactone)/polylactic (PCL/PLA) blend foam vascular scaffolds were fabricated by supercritical carbon dioxide via batch foaming. A uniform open-cell morphology on the cross section of PCL/PLA foams was achieved. To improve the porosity and hydrophilicity on the surface of scaffolds, sodium hydroxide solution was used to hydrolyze off PLA phase. Tensile properties, suture retention, bursting resistance and cell culture of PCL/PLA foam scaffolds were also improved and showed a great promise for vascular tissue engineering application.

Fabrication of Novel Open-Cell Foams of Poly(ε-caprolactone)/Poly(lactic acid) Blends for Tissue-Engineering Scaffolds

Poly(ε-caprolactone)/poly(lactic acid) (PCL/PLA) blends are very promising materials with biodegradable characteristics and tailorable performance for many applications. In this study, PCL and PLA were compounded at various ratios using a co-rotating twin-screw extruder. The morphology showed that they were immiscible but were dispersed well in each other. Very interesting and peculiar open-cell structures were obtained through a batch-foaming process. Interconnected holes with flexible PCL fibrils were created by high tensile stress during cell expansion, which contributed to the rapid diffusion of CO2. No cells collapsed at high foam expansion under all foaming conditions. Moreover, a small-diameter tubular PCL/PLA foamed scaffold had a tensile toe region of approximately 40%, which indicated a potential application for vascular tissue engineering. The human umbilical vein endothelial cells cultured on the surfaces of PCL/PLA blend foams showed high viability and migration.

Preparation and properties of flexible poly(lactic acid) blend foams

High-performance poly(lactic acid) (PLA) foam has been recognized as a promising material because of its biodegradability. However, low flexibility and foamability of PLAs has limited its use in different fields. In this study, a blend-toughening technology was used to toughen PLA and prepare flexible foams. The mechanical properties of PLA blends were evaluated, and the cellular structure of these foaming blends was characterized. The results show that the blending components significantly affected the overall mechanical properties and foaming behavior of PLA. The toughness of PLA was enhanced by adding poly(butylene adipate- co-terephthalate) (PBAT) and rigid particles. The rheological behavior of PLA was also affected by adding PBAT. Therefore, the cellular structure of the PLA foams was affected. A constitutive model was also used to fit the experimental results of the compression property of the PLA foam.

Preparation, Foaming and Characterization of Poly(l-lactic acid))/Poly(d-lactic acid)-Grafted Graphite Oxide Blends

Abstract Commercial poly(l-lactic acid) (PLLA) was blended with different contents of graphene oxide-graft-poly(d-lactic acid) (GO-g-PDLA), which was synthesized via ring-opening polymerization using modified GO as initiator. PLLA and PLLA/GO-g-PDLA blend foams were prepared in a batch process via varying-temperature mode using supercritical carbon dioxide as physical foaming agent. The results showed that the addition of GO-g-PDLA in PLLA leads to the formation of stereocomplex (sc)-crystallites. Increase in the GO-g-PDLA content enhances the IR absorption, diffraction peak and melting peak corresponding to the sc-crystallites. The addition of GO-g-PDLA to PLLA leads to the decrease of the cell diameter, increase of the cell density and to a little change in expansion ratio, which is attributed to the fact that the enhancement of PLLA crystallization restricts cell growth and GO-g-PDLA acts as nucleation point.

Kinetics study of oil sorption with open‐cell polypropylene/polyolefin elastomer blend foams prepared via continuous extrusion foaming

The objective of the present work was to study the sorption kinetics of open‐cell polypropylene/polyolefin elastomer (PP/POE) blend foams. First, open‐cell PP/POE foams of different cell structures were prepared by controlling the foaming temperature via a continuous extrusion foaming process. Second, the effect of the cell structures on the sorption process, rate, and capacity was studied. Pseudo‐first order and pseudo‐second order models were applied to study the sorption kinetics of the PP/POE foams for cyclohexane. Third, the sorption rate and sorption capacity by both volume and weight of the PP/POE foam for different oils and solvents were studied to show how the intrinsic properties of the testing oils and solvents affected the sorption performance. The results showed that the sorption with the PP/POE foams followed the pseudo‐second order kinetics model. Both the cell structures of the foams and the intrinsic properties of the testing oils and solvents affected the sorption performance. For the same testing oil, a higher open‐cell content in the foam was favorable for a higher sorption rate, and a higher void fraction was favorable for a higher sorption capacity. For the same foam, a lower viscosity of the testing oil was favorable for a higher sorption rate. The sorption capacity by volume was closely related to the viscosity of the testing oil, while both the viscosity and the density of the testing oil determined the sorption capacity by weight.

Effect of the Citric Acid as Blowing Agent on the Compressive Properties and Morphology of PLA/ENR Blend Foams

The effect of a blowing agents that affected Polylactic acid (PLA) and Epoxidized natural rubber (ENR) the blowing agents composed of citric acid (CA) and sodium hydrogen carbonate (NaHCO3) mixing by twin screw extruder with co-rotation screw. The properties of biodegradable foams were investigated. Blended foams of all composition were prepared by using compression molding at 200°C using different proportions of PLA, ENR, CA and NaHCO3. Mechanical properties of the samples were characterized by using universal testing machine. Thermal properties including Glass transition temperature (Tg), crystallization temperature (Tc) and melting temperature (Tm) were examined by using differential scanning calorimetry (DSC). Physical properties including morphology and density of blended foams were also investigated and morphological properties were studied with a scanning electron microscope (SEM).

Effect of nanosize CaCO3 and nanoclay on morphology and properties of linear PP/branched PP blend foams

Branched polypropylene (PP) polymer (BPP), two nanoparticles with different aspect ratios, nano CaCO3, and nanoclay (Cloisite 20A), were used for improving the melt strength of linear PP (LPP) and producing microcellular foam via a solid‐state foaming process using supercritical N2 as a physical foaming agent. The effects of BPP and nanoparticles were investigated on the rheological and mechanical properties of the nanocomposite and morphological properties of the foamed samples. The effect of temperature, saturation pressure, and foaming time were studied on the morphological properties of the foams, too. The results showed that the BPP increased the elongation at break of nanocomposite samples, and nano CaCO3 increased tensile strength, elongation at break, and tensile modulus, except at its highest content (15 wt%) and improving the dispersion of nanoclay. The nanoclay improved tensile strength and tensile modulus of nanocomposites, except at its highest content (6 wt%). The nanoclay increased the cell density and reduced the cell size and improved melt strength and cell stability during the foaming process. The nano CaCO3 improved foamability, cell size, and cell density. The simultaneous presence of nanoclay and nano CaCO3 synergistically improved the cell density and decreased the cell size of the foams. The best process conditions were found as 140°C temperature, 80 bar pressure, and 2 h time. The results of the DSC analysis showed that the crystallinity of foamed samples was higher than the nanocomposites and DMTA analysis showed that the tan δ of foamed samples was higher than unfoamed samples. POLYM. COMPOS., 40:E227–E241, 2019. © 2017 Society of Plastics Engineers