Thermoformable high oxygen barrier multilayer EVOH/LDPE film/foam

The effect of the number of layers on oxygen transmission and thermoformability of novel multilayer film/foam materials was investigated. Ethylene-vinyl alcohol copolymer/low-density polyethylene multilayered film/foam composites having 16, 32, and 64 alternating layers were developed using continuous multilayer coextrusion process, and the morphology, density, oxygen transmission, and mechanical properties of the as-extruded film/foams were characterized. Tensile properties of the film/foams at elevated temperatures were used to optimize thermoforming conditions. Uniaxial orientation was discovered as an efficient approach to evaluate the potential for thermoforming. Oxygen transmission showed a strong correlation with the thickness reduction which could be used as an indicator for barrier properties of the packaging materials. Film/foam materials with 32 layers demonstrated optimum performance with low oxygen transmission along with high drawing capability. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48903.     

A high‐barrier PP/EVOH membrane prepared through the multistage biaxial‐stretching extrusion

The polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) membranes were prepared by a novel extrusion die with an assembly of laminating‐multiplying elements (LMEs). A biaxial‐stretching occurred when polymer melts flowing through a LME. The morphology development of PP/EVOH blends and its effect on gas‐barrier property, solvent‐absorption property and mechanical properties were characterized by scanning electron microscope (SEM), polarized optical microscope (POM), gas‐permeability test, immersion experiment, differential scanning calorimetry (DSC), and tensile test. With the introduction of LME and the increasing of its number, morphology of EVOH phase in PP matrix gradually changed from zero‐dimension spherical particles to one‐dimension fibers, and then to two‐dimension sheets. As a result, the nitrogen permeability coefficient decreased nearly by two orders of magnitude and the permeability coefficient of toluene‐PP/EVOH system declined by almost four times. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45016.     

Polymer ferroelectret based on polypropylene foam: Piezoelectric properties improvement using post‐processing thermomechanical treatment

In this work, the effect of post‐processing parameters (time, temperature, and pressure) on the morphology as well as mechanical and piezoelectric properties of foamed polypropylene (PP) films were studied. Two different post‐processing methods, based on the saturation of a foamed film with supercritical nitrogen (N₂), were used to obtain an optimized eye‐like cellular structure with a high cell aspect ratio (AR). The results showed that, when the PP‐foamed films were exposed to a gradual temperature and pressure increase, an appropriate cellular structure with high AR value (about 6.6) was obtained. This structure led to a high quasi‐static piezoelectric d₃₃ coefficient of 800 pC/N (45% higher than for untreated ones) indicating the importance of the post‐processing treatment on the piezoelectric behavior of these films. On the other hand, when the treatment was performed in steps, cell morphology changed from an eye‐like to a less elongated shape, resulting in lower d₃₃ values. The tensile characterization showed that higher cell aspect ratio led to lower Young's modulus, which is suitable to achieve higher piezoelectric properties. Finally, dynamic mechanical analysis (DMA) was used as a simple method to correlate mechanical and piezoelectric properties of cellular PP. This was done via the ratio of the storage moduli in the longitudinal and transverse directions, which is directly related to film anisotropy (AR value) and thus to the piezoelectric behavior. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44577.     

Polyurethane/clay nanocomposites with improved helium gas barrier and mechanical properties: Direct versus master‐batch melt mixing route

Thermoplastic polyurethane (TPU)/clay nanocomposite films were produced by incorporation of organo‐modified montmorillonite clay (Cloisite 30B) in TPU matrix by two different melt‐mixing routes (direct and master‐batch‐based mixing), followed by compression molding. In master‐batch mixing where the master‐batch was prepared by mixing of clay and TPU in a solvent, better dispersion of clay‐layers was observed in comparison to the nanocomposites produced by direct mixing. As a consequence, superior mechanical and gas barrier properties were obtained by master‐batch mixing route. The master‐batch processing resulted in 284 and 236% increase in tearing strength and tearing energy, respectively, with 5 wt % clay‐loading. Interestingly, in case of master‐batch mixing, the tensile strength, stiffness as well as breaking extension increased simultaneously up to 3 wt % clay‐loading. The helium gas permeability reduced by about 39 and 31% for the TPU/clay nanocomposites produced by mater‐batch and direct mixing routes, respectively, at 3 wt % loading of clay. Finally, the gas permeability results have been compared using three different gas permeability models and a good correlation was observed at lower volume fraction of clay. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46422.     

Hierarchical structure and properties of rigid PVC foam crosslinked by the reaction between anhydride and diisocyanate

Rigid crosslinked poly(vinyl chloride) (c‐PVC) foams by forming semi‐interpenetrating network (SIPN) structure via the reaction of phthalic anhydride (PA) and diisocyanate were prepared. The influence of PA on hierarchical structure and mechanical properties of c‐PVC foam was studied. The Fourier transform infrared spectrometer results showed that the presence of PA resulted in the formation of imide structure in the SIPN of obtained c‐PVC foams, which introduced a structural defect of SIPN. Thus, the residue (gel) from tetrahydrofuran extraction of the foams decreased with the increase of PA content. Dynamic thermal analysis showed the presence of three aggregation state structures in the c‐PVC foams, depending on the loading of PA. The addition of PA in the formulations affected cellular structure and mechanical properties of the obtained foams. Furthermore, the influence of chemical environment of anhydride compounds on the formation of imide structure in the crosslinking network of c‐PVC foams was discussed. A strategy for reducing defect of crosslinking network and improving mechanical properties was put forward. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46141.     

Factors influencing resorcinol–formaldehyde–latex‐coated continuous basalt fiber cord/rubber interfacial fatigue behavior: Loading direction and RFL formula

In this study, samples were prepared with resorcinol–formaldehyde–latex (RFL)‐coated continuous basalt fiber (CBF) cords and a natural rubber (NR)/styrene–butadiene rubber (SBR) matrix for interfacial fatigue tests under periodic radial loading conducted using a De Mattia Rubber Flexometer. The effects of the RFL formula on the interfacial fatigue behavior, including the fatigue life and the evolution of residual adhesion strength, were the focus of this work. The fatigue behavior was compared with that under axial loading. The results showed that under radial loading, the residual adhesion strength of the samples remained higher than that under axial loading, and the evolution of adhesion was divided into three stages. The adhesion improvement in the second stage was due to further cocrosslinking between the rubber matrix and the latex in the RFL layer, and the duration of the second stage was determined by the amount of reactive latex in the RFL layer. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46619.     

Structure evolution driven by phase separation and the corresponding foaming behavior of polystyrene/poly(methyl methacrylate) blends via a batch foaming process

Morphology evolution of immiscible polymer blends during processing is a common phenomenon, but how it affects the foaming behavior is still unknown. The present work aims to study the effect of morphology evolution of polystyrene/poly(methyl methacrylate) (PS/PMMA) blends driven by phase separation on foaming behavior via a batch foaming process. Morphology evolution of PS/PMMA blends were conducted via thermal annealing using a compression molding machine. Phase contrast optical microscope and scanning electron microscope were used to investigate the morphology evolution and cell structures. The diffusion coefficients were calculated to study the effect of morphology evolution on gas diffusion behavior. It was found that phase domain was increased in size with the annealing and that cell structure was significantly dependent on morphology evolution. The thermal annealing with a long time could dramatically impact cell structures, especially for the blends with a bi‐continuous phase structure or a sea‐island structure with very large phase domains. The diffusion coefficient for the interface was increased with the annealing, which resulted in the generally decreased expansion ratio. Therefore, annealing for a long time at melt states during processing should be avoided for obtaining well‐defined cell structures for immiscible polymer blends. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46704.     

A quantitative evaluation method of the barrier property of the residue for flame retardant polymers

To investigate the flame retardant properties and mechanisms of those fire retardant polymer systems that mainly depend on the produced protective char shields, quantitative analysis for the barrier quality of the char layer is important but still a challenge. In the present article, a novel and simple characterization method based on atmosphere permeability is proposed to quantitatively evaluate the barrier property: an incombustible fabric carrier coated with the flame retardant polymer solution, is carbonized at high temperature to make the produced char residue adhered to the fabric. As the interfibrous gaps are filled and closed by the chars, the atmosphere permeability of the heated fabric decreases compared with that of original one. Their difference value can really reflect the contribution of the charring residue to the barrier property. This method combined with other characterizations including residue morphology observation, vertical burning test, limiting oxygen index, and calorimetric analysis, is very helpful to reveal the correlation between the flame retardance and barrier property of the char residue, evaluate the flame retardant efficiency in the condense phase, and estimate the corresponding flame retardant mechanisms. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45102.     

Triple‐shape‐memory polymer films created by forced‐assembly multilayer coextrusion

Triple‐shape‐memory polymers are capable of memorizing two temporary shapes and sequentially recovering from the first temporary shape to the second temporary shape and eventually to the permanent shape upon exposure to a stimulus. In this study, unique three‐component, multilayered films with an ATBTA configuration [where A is polyurethane (PU), B is ethylene vinyl acetate (EVA), and T is poly(vinyl acetate) (PVAc)] were produced as a triple‐shape‐memory material via a forced‐assembly multilayer film coextrusion process from PU, EVA, and PVAc. The two well‐separated thermal transitions of the PU–EVA–PVAc film, the melting temperature of EVA and the glass‐transition temperature of PVAc, allow for the fixing of the two temporary shapes. The cyclic thermomechanical testing results confirm that the 257‐layered PU–EVA–PVAc films possessed outstanding triple‐shape‐memory performance in terms of the shape fixity and shape‐recovery ratios. This approach allowed greater design flexibility and simultaneous adjustment of the mechanical and shape‐memory properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44405.     

Processing–morphology–property relationships of polypropylene–graphene nanoplatelets nanocomposites

Polypropylene (PP) nanocomposites reinforced with graphene nanoplatelets (GNPs) were prepared via melt extrusion. A special sheet die containing with two shunt plates was designed. The relationships among the flow field of the special die, exfoliation, and dispersion morphology of the GNPs in PP and the macroscopic properties of the nanocomposites were analyzed. Flow field simulation results show that the die with shunt plates provided a high shear stress, high pressure, and high velocity. The differential scanning calorimetry, X‐ray scattering, and electron microscopy results reveal that the nanocomposites prepared by the die with the shunt plates had higher crystallinity values and higher exfoliation degrees of GNPs. The orientation of the GNPs parallel with the extrusion direction was also observed. The nanocomposites prepared by the die with shunt plates showed a higher electrical volume conductivity, thermal conductivity, and tensile properties. This indicated that the high shear stress exfoliated the GNPs effectively to a thinner layer and then enhanced the electrical, thermal, and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44486.     

Influence of different compatibilizers on the morphology and properties of PA6/PET/glass fiber composites

Three kinds of compatibilizers, ethylene–ethyl acrylate copolymer (EEA), ethylene–ethyl acrylate–glycidyl methacrylate copolymer (EAG), and ethene–maleic anhydride–glycidyl methacrylate copolymer (EMG), were introduced to PA6/PET/GF blends for the first time to study the effect of different compatibilizers on composite. EEA, EAG, and EMG showed different effect on the properties of PA6/PET/GF blends. An observation of the GF–resin interface by scanning electronic microscope indicated EAG and EMG enhanced the adhesion of resin to GF, while EEA exhibited no improvement. Differential scanning calorimetry analysis showed that both EMG and EAG increased the degree of crystallinity of the PA6/PET/GF blends, whereas EEA declined. According to dynamic mechanical analysis, EAG, and EMG remarkably increased the storage modulus of composites. For the composites at a given GF content of 30 wt %, EMG increased the tensile strength from 140.6 to 156.3 MPa. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46429.     

Positive temperature coefficient effect and mechanism of compatible LLDPE/HDPE composites doping conductive graphite powders

Linear low density polyethylene (LLDPE)/high density polyethylene (HDPE) blends doped conductive graphite powders were constructed by the traditional melt‐blending method to acquire the conductive compatible polymer composites, and corresponding positive temperature coefficient (PTC) effect of electrical resistivity was investigated. The results indicated that the room‐temperature resistivity gradually decreased and PTC effects were remarkably enhanced by regulating the graphite contents or LLDPE/HDPE ratios. Especially, with increasing graphite contents, the polymer‐fixed composites showed the notable double PTC effects, originating from the volume expansion of the co‐crystallization or their fraction. Whereas, with increasing the LLDPE/HDPE ratio, the PTC effects of the graphite‐fixed composites occurred at the lower temperature, even far below the melting points of the co‐crystallization. Therefore, the regulation of co‐crystallization morphology of compatible polymer matrices was a new idea in the improvement of PTC materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46453.     

Structure–property modification of microcrystalline cellulose film using agar and propylene glycol alginate

Microcrystalline cellulose gum (MCG) forms edible films with poor physical and barrier properties. This study investigated the effects of incorporated agar and propylene glycol alginate (PGA) on structure and property of MCG films. The addition of agar and PGA modified the microstructure and reduced pinholes contributed to lower water vapor permeability (WVP) and improved tensile property of agar–MCG films. However, PGA–MCG had reduced tensile strength possibly due to incompatibility between polymer networks, however, showed a synergistic light barrier. The increased surface hydrophobicity (θ ～ 30°–75°) correlated well with decreased WVP for agar, PGA, and their composites which diverted from pure MCG films. The MCG reduced the thermal stability of agar; however, the PGA had no effect. Conversely, agar and PGA increased the thermal stability of the MCG component. The infrared spectra revealed insignificant H‐bonding and molecular interaction between polymers. Therefore, the results indicated that agar and PGA improved stability, mechanical, and barrier properties of edible MCG films via physical entanglement. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45533.     

Determination of highly porous plastic foam structural characteristics by processing light microscopy images data

Mathematical modelling of physical and mechanical properties of plastic foam as well as numerous practical applications requires knowledge of foam structural characteristics. A necessity exists to determine the characteristics of the spatial structure of inhomogeneous materials comprising inclusions of other material, e.g., polyurethane foam without destructing the material and analysis of each element. A methodology is elaborated for preparing highly porous plastic foam specimens and investigation of foam strut‐like structure with light microscopy (LM) by taking images in three mutually perpendicular planes. A mathematical model is developed for highly porous plastic foam for the determination of probability density functions of its building elements—polymeric struts': (a) length and (b) angles, using LM images in three mutually perpendicular planes. Computer codes are created and parameters of distribution functions for strut's length and angles are calculated using experimental data for verification. A good correspondence of the modelling results with experimental data is proved to exist. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39477.     

Investigations of environmental stress cracking resistance of HDPE/EVA and LDPE/EVA blends

HDPE/poly(ethylene‐co‐vinylacetate) (EVA) and low‐density polyethylene (LDPE)/EVA blends were tested and compared with respect to their environmental stress cracking resistance (ESCR) using the Bell‐telephone test. The time to failure in the ESCR test improves with increasing EVA content, and considerable improvements were produced for LDPE/EVA blends while small improvements were observed for HDPE/EVA blends. Thermal, rheological, mechanical, and morphological studies were conducted which established a quantitative relationship between morphological features and composition. Furthermore, the failed specimens were further characterized by scanning electron microscopy and fractographic methodology to investigate the failure mechanism for ESCR samples. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39880.     

Facile fabrication of polyimide foam sheets with millimeter thickness: Processing,morphology, and properties

A series of polyimide foam sheets (PIFSs) with thickness of 0.5 mm using 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 3,4′‐oxydianiline (3,4′‐ODA), and polyaryl polymethylene isocyanate (PAPI) as main materials were first fabricated by liquid foaming and compression molding technology. The effects of different PAPI contents and 3,4′‐ODA contents on the structures and properties of PIFSs were investigated. The results indicated that PIFSs exhibited a structure that front surface displayed closed cells made of damaged cell walls and membranes, while internal cells were open, and elliptic vacancies were flatted in the thickness direction from the cross section. The average cellular diameter increased with increasing PAPI loading. In addition, the introduction of 3,4′‐ODA increased the average cell size of PIFSs. Further, PIFSs had density of 0.087–0.239 g/cm³, elongation at break of 3.75–8.01% and tensile toughness of 3.46 × 10^?2?13.87 × 10^?2 J/cm³. Notably, they exhibited higher tensile strength of 1.89–5.42 MPa and lower thermal conductivity of 14.727–19.25 mW/m ?K at 24°C, compared to the polyimide foams reported earlier. The sound absorption coefficients (α) of samples with different PAPI contents increased and then decreased with increasing PAPI content. At low frequencies, a certain content of 3,4′‐ ODA allowed an improvement of the acoustical behavior of PIFSs, and the α increased and then decreased with increasing density. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39881.     

Development of a melt‐extrudable biobased soy flour/polyethylene blend for multilayer film applications

Monolayer and multilayer films from biobased linear low‐density polyethylene and milled soy flour were produced through cast film coextrusion processes using conventional thermoplastic processing equipment. Films containing 10 and 20% by weight of soy flour milled to maximum particle sizes of 8, 11, and 22 µm were extruded and characterized as a packaging film material. Water resistance, tensile properties, and gas permeability were measured on each film and analyzed with respects to the soy particle size, soy loading, and layer configuration in the multilayer film structure. Mechanical properties results indicated that ultimate elongation of the soy‐containing films decreased by as much as 14% compared to the control, while tensile strength and maximum load testing did not reveal any identifiable trends. Monolayer soy‐containing film showed high moisture sensitivity, as measured by contact angle and absorption testing, while the multilayer films demonstrated a more hydrophobic nature as indicated by higher contact angle measurements. This increase in hydrophobic properties is due to protective polyolefin skin layers, which are more hydrophobic. Oxygen transmission rates of the multilayer films decreased by 38% due to the presence of soy flour as compared to the control that did not contain any soy flour. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40707.     

Research on properties of rigid polyurethane foam with heteroaromatic and brominated benzyl polyols

Rigid polyurethane foams (RPUFs) were prepared with specific heteroaromatic and brominated benzyl polyols. The mechanical properties and thermal stability were studied using dynamic mechanical analysis (DMA) and thermogravimetric analysis (TG). The limiting oxygen index (LOI) was used to investigate the flame retardancy of the RPUFs. The results showed that the glass transition temperature (T_g) of the RPUF prepared by heteroaromatic polyol was 182°C, demonstrating an improved thermal stability for this specific heteroaromatic polyol. Brominated benzyl polyol exhibited less negative influence on mechanical properties of the RPUFs at the same time of improving the flame retardancy. The LOI values increased with an increase in the brominated polyol content to 27.5%, and the char‐forming ability of the RPUF improved; the char residue rate reached 12.6% at 700°C, but it was only 6.2% without the flame retardant. Scanning electron microscope (SEM) and energy‐dispersive spectrometry (EDS) verified that the mechanism of flame retardancy was due to a synergistic effect of the gas phase and the condensed phase. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42349.     

Gloss reduction and morphological properties of polycarbonate and poly(methyl methacrylate‐acrylonitrile‐butadiene‐styrene) blends with SAN‐co‐GMA as a reactive compatibilizer

The gloss properties of the polycarbonate (PC)/poly(methyl methacrylate‐acrylonitrile‐butadiene‐styrene) (MABS) blend with styrene‐acrylonitrile‐co‐glycidyl methacrylate (SAN‐co‐GMA) as a compatibilizing agent were investigated. For the PC/poly(MABS)/SAN‐co‐GMA (65/15/20, wt %) blend surface, the reduction of gloss level was observed most significantly when the GMA content was 0.1 wt %, compared with the blends with 0.05 wt % GMA or without GMA content. The gloss level of the PC/poly(MABS)/SAN‐co‐GMA (0.1 wt % GMA) blend surface was observed to be 35, which showed 65% lower than the PC/poly(MABS)/SAN‐co‐GMA blend without GMA content. The gloss reduction was most probably caused by the insoluble fractions of the PC/poly(MABS)/SAN‐co‐GMA blend that were formed by the reaction between the carboxylic acid group in poly(MABS) and epoxy group in SAN‐co‐GMA. The results of optical and transmission electron microscope analysis, spectroscopy study, and rheological properties supported the formation of insoluble structure of the PC/poly(MABS)/SAN‐co‐GMA blend when the GMA content was 0.1 wt %. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46450.     

Electrical percolation behavior of carbon fiber and carbon nanotube polymer composite foams: Experimental and computational investigations

The effect of foaming on the electrical percolation of polymer composites was simulated by a random sequential additional (RSA) process. Polystyrene composites containing various amounts of carbon fiber (CF) and carbon nanotubes (CNTs) were prepared through melt blending in an internal mixer and subsequently compression‐molded to solid and foam sheets. The electrical conductivity (EC) and percolation threshold (P_c) of both the solid and foam composites were determined to evaluate the simulation results. The experimental results show that the EC of the CF composites decreased with foaming, whereas for the CNT composites, no significant change was observed. The RSA process was used to construct the microstructure of the solid and foam composites and predict their P_cs. Several parameters, including the fiber aspect ratio, bubble volume fraction, and bubble size, were studied by the simulation approach. The P_cs obtained by simulation showed good agreement with the experimental values. When bubbles were excluded to define the volume fraction of the filler, the foam composites with bubbles, close to the fibers in size, had approximately the same P_cs as the solid composites. Better agreement between the experimental and simulation results was found for the foam composites with 30 vol % bubbles rather than those with 15 vol %. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42685.