LDPE composite films incorporating ceramic powder emitting far‐infrared radiation for advanced food‐packaging applications

A ceramic powder that emits far‐infrared radiation (FIR) was incorporated into low‐density polyethylene (LDPE) via melt‐compounding and subsequent melt‐extrusion processes. To investigate the feasibility of as‐prepared LDPE/FIR composite films for use in packaging applications, the composite films were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, FIR emissivity and emissive power, antimicrobial activity assays, and storage tests. The physical properties and antimicrobial activities of the composite films were found to strongly correlate with the changes in the chemical and morphological structures that originate from different contents of FIR ceramic powder. A higher content of FIR ceramic powder in the LDPE/FIR composite film provided increased FIR emissivity and emission power of the composite and resulted in good antimicrobial activity. Storage tests also showed that incorporation of FIR ceramic powder into LDPE film was an effective method for maintaining the freshness of lettuce. Furthermore, the incorporation of FIR ceramic powder into LDPE films induced higher thermal stability and crystallinity and enhanced their barrier properties, which suggest these LDPE/FIR composite films are potential candidates for advanced packaging materials for the food and medical industries. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43102.     

Influence of melt processing on biodegradable nisin‐PBAT films intended for active food packaging applications

Biodegradable poly(butylene adipate‐co‐terephthalate) (PBAT) films incorporated with different levels of the antimicrobial peptide nisin were developed by melt processing. Structural, morphological, thermal, mechanical, and antimicrobial properties of the films were determined. The X‐ray diffraction patterns exhibited decreasing levels of intensity at 2θ values as the concentration of nisin increased. Scanning electron microscopy showed a heterogeneous morphology when higher amounts of nisin were incorporated. The antimicrobial films tested presented no significant differences in the melting temperature (123–125°C), and the crystallization temperature ranged from 69 to 75°C. The addition of nisin caused no significant modification in tensile strength values. However, results of Young's modulus and deformation at break differed significantly among samples. Active films demonstrated inhibition against the Gram‐positive bacterium Listeria monocytogenes. These results demonstrated that PBAT/nisin films produced by melt processing present a great potential for use as active food packaging materials aiming enhanced food safety. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43212.     

Electrolytically exfoliated graphene–polylactide‐based bioplastic with high elastic performance

This work reports an innovative way to prepare biopolymer composite by incorporating graphene (GP) synthesized from electrolytic exfoliation into biodegradable polymer blend (polylactide/epoxidized palm oil: PLA/EPO) based on melt‐blending method and studies their physical properties for food packaging and related applications. Multilayer GP structure synthesized by electrolytic exfoliation is confirmed by transmission electron microscopy and Raman spectroscopy, whereas homogeneous GP incorporation in PLA/EPO is verified by scanning electron microscopy and X‐ray diffraction. From thermogravimetric analysis and heat deformation temperature (HDT) studies, the decomposition and HDTs of PLA/EPO/GP composites are higher than those of PLA/EPO but are lower than those of pristine PLA and tend to decrease with increasing GP content because of thermal conductivity effect. From standard tensile test, loading of GP in PLA/EPO at an optimal concentration of 0.6 wt % results in higher elongation at break by as much as 52%. The observed additional elongation under a given tension and the corresponding lower tensile strength/Young's modulus may be attributed to lower binding force of materials in the composite because of the presence of relatively weak GP–PLA/EPO interfaces. Moreover, oxygen permeability is found to decrease with increasing GP contents and oxygen permeability is reduced by 40.33% at the GP loading concentration of 0.6 wt %. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41439.     

Electrospun nylon 6 nanofibers incorporated with 2‐substituted N‐alkylimidazoles and their silver(I) complexes for antibacterial applications

The article presents the incorporation of biocides [2‐substituted N‐alkylimidazoles and their silver(I) complexes] into electrospun nylon 6 nanofibers for application as antimicrobial materials. The electrospun nylon 6/biocides nanofiber composites were characterized by IR spectroscopy (ATR‐FTIR) and scanning electron microscopy (SEM‐EDX). The antimicrobial activity of the electrospun nylon 6/biocides nanofiber composites was evaluated against Escherichia coli, Staphylococcus aureus, and Bacillus subtilis subsp. spizizenii using the disk diffusion method, the American Association for Textile Chemists and Colorists test method 100‐2004 and the dynamic shake flask method (American Society for Testing and Materials E2149‐10). The electrospun nylon 6 nanofibers incorporated with 2‐substituted N‐alkylimidazoles displayed moderate to excellent levels of growth reduction against S. aureus (73.2–99.8%). For the electrospun nylon 6 nanofibers incorporated with silver(I) complexes, the levels of growth reduction were >99.99%, for both E. coli and S. aureus, after the antimicrobial activity evaluation using the shake flask method. The study demonstrated that the electrospun nanofibers, fabricated using the incorporation strategy, have the potential to be used as attractive antimicrobial materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39783.     

Nonisothermal crystallization kinetics and morphology of poly(ethylene terephthalate) modified with poly(lactic acid)

The nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) copolymers modified with poly(lactic acid) (PLA) were investigated with differential scanning calorimetry, and a crystal morphology of the samples was observed with scanning electron microscopy. Waste PET (P100) obtained from postconsumer water bottles was modified with a low‐molecular‐weight PLA. The PET/PLA weight ratio was 90/10 (P90) or 50/50 (P50) in the modified samples. The nonisothermal melt‐crystallization kinetics of the modified samples were compared with those of P100. The segmented block copolymer structure (PET‐b‐PLA‐b‐PET) of the modified samples formed by a transesterification reaction between the PLA and PET units in solution and the length of the aliphatic and aromatic blocks were found to have a great effect on the nucleation mechanism and overall crystallization rate. On the basis of the results of the crystallization kinetics determined by several models (Ozawa, Avrami, Jeziorny, and Liu–Mo) and morphological observations, the crystallization rate of the samples decreased in the order of P50 > P90 > P100, depending on the amount of PLA in the copolymer structure. However, the apparent crystallization activation energies of the samples decreased in the order of P90 > P100 > P50. It was concluded that the nucleation rate and mechanism were affected significantly by the incorporation of PLA into the copolymer structure and that these also had an effect on the overall crystallization energy barrier. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Preparation of pectin‐inorganic composite material as accumulative material of metal ions

Pectin is one of the biopolymers in the cell walls of all plant tissues, but the pectin‐containing materials have been discarded as industrial waste in food‐processing factories. We prepared a water‐insoluble pectin‐inorganic composite material by mixing pectin and a silane coupling reagent, bis(3‐trimethoxysilylpropyl)amine. The mechanical strength of the pectin‐inorganic composite material was higher than that of the pectin material without the addition of an inorganic component. In addition, the thermal stability of the composite material increased with the addition of the inorganic component. Furthermore, when the pectin‐inorganic composite materials were incubated in an aqueous solution of Cu(II), Zn(II), or In(III), these composite materials effectively accumulated not only the heavy metal ions, but also rare‐earth metal ions. Additionally, based on the infrared (IR) measurements, the metal ion accumulative mechanism into the composite material is described. As a result, the IR spectra suggested an electrostatic interaction between the metal ion and carboxy group in the pectin. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42056.     

Interfacially compatibilized poly(lactic acid) and poly(lactic acid)/polycaprolactone/organoclay nanocomposites with improved biodegradability and barrier properties: Effects of the compatibilizer structural parameters and feeding route

Nanocomposites with enhanced biodegradability and reduced oxygen permeability were fabricated via melt hybridization of organomodified clay and poly (lactic acid) (PLA) as well as a PLA/polycaprolactone (PCL) blend. The nanocomposite microstructure was engineered via interfacial compatibilization with maleated polypropylene (PP‐g‐MA). Effects of the compatibilizer structural parameters and feeding route on the dispersion state of the nanolayers and their partitioning between the PLA and PCL phases were evaluated with X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy. Although highly functionalized PP‐g‐MA with a low molecular weight was shown to be much more effective in the intercalation of PLA and the PLA/PCL blend into the clay gallery spaces, composite samples compatibilized by high‐molecular‐weight PP‐g‐MA with a lower degree of maleation exhibited lower oxygen permeability as well as a higher rate of biodegradation, which indicated the accelerating role of the dispersed nanolayers and their interfaces in the enzymatic degradation of PLA and PLA/PCL matrices. This evidenced a correlation between the nanocomposite structure and rate of biodegradation. The size of the PCL droplets in the PLA matrix was reduced by nanoclay incorporation, and this revealed that the nanolayers were preferentially wetted by PCL in the blend. However, PCL appeared as fine and elongated particles in the microstructure of the PLA/PCL/organoclay hybrids compatibilized by higher molecular weight and less functionalized PP‐g‐MA. All the PLA/organoclay and PLA/PCL/organoclay hybrids compatibilized with high‐molecular‐weight PP‐g‐MA displayed a higher dynamic melt viscosity with more pseudo solid‐like melt rheological responses, and this indicated the formation of a strong network structure by the dispersed clay layers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Micromorphology,mechanical, crystallization and permeability properties analysis of HA/PBAT/PLA (HA,hydroxyapatite; PBAT,poly(butylene adipate‐co‐butylene terephthalate); PLA,polylactide) degradability packaging films

In this study, the self‐made nano‐hydroxyapatite (HA) and poly(butylene adipate‐co‐butylene terephthalate) copolyesters (PBAT) were used as fillers, and composite films of HA/PLA (PLA, polylactide) and HA/PBAT/PLA systems were prepared. The micromorphology, mechanical properties, thermal properties, crystallinity, water vapor permeability and oxygen permeability of the composite films were studied. The results show that the self‐made HA has a porous rod‐like structure with a size of 30–50 nm. PBAT was dispersed uniformly in the HA/PLA matrix in the form of spherical particles and formed many pores and holes. The tensile strength, elongation at break and modulus of elasticity of HA/PLA composite films were increased by adding 10 wt% PBAT. The addition of HA and PBAT played a synergistic function in improving the crystallinity of the composite films. The water vapor and oxygen permeabilities of HA/PLA and HA/10%PBAT/PLA composite films can be regulated by adjusting the amount of HA. The results of this study indicate that composite films with higher water vapor and oxygen permeabilities exhibit great potential for applications in green packaging and fresh‐keeping packaging. © 2019 Society of Chemical Industry     

Antimicrobial activity of PLA/PEG nanofibers containing terpinen‐4‐ol against Aggregatibacter actinomycetemcomitans

In this article, nanofibrous mats of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) with different PLA/PEG ratios were prepared by solution blow spinning. Terpinen‐4‐ol, a major phytoconstituent from tea tree oil (Melaleuca alternifolia) was added to the fibers and their antimicrobial activity against Aggregatibacter actinomycetemcomitans (ATCC 00078) was tested. Spun mats were characterized by scanning electron microscopy, thermogravimetric analyses, differential scanning calorimetry, Fourier‐transform infrared spectroscopy (FTIR), and cell viability tests by biofilm grown on the surface of inhibitory fibers. Fibers had average diameters dependent on polymer ratio. PEG acted as a plasticizer resulting in a reduction in PLA crystallinity. Addition of PEG lead to a faster drug release. Fibrous mats with terpinen‐4‐ol, whose incorporation was verified by FTIR, showed an effective antimicrobial activity against A. actinomycetemcomitans, similar to those containing 0.12% chlorhexidine gluconate (P < 0.05), used as both the positive control and the dose level recommended for patient treatment. These results confirm the potential of solution blow spun fibrous mats containing terpinen‐4‐ol in the treatment of aggressive periodontitis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45782.     

Biodegradable antimicrobial films based on poly(lactic acid) matrices and active azo compounds

Using solvent casting and melt compounding methods, we realized antibacterial and antifungal poly(lactic acid)‐based films by introducing different percentages of antimicrobial azo dyes into polymer matrices. Concentration up to 0.01% (w/w) of azo compounds permitted the preparation of antimicrobial and transparent films. The thin films retained the properties of the pure PLA matrices, such as glass transition temperature, flexibility, and amorphous nature. The films exhibited antimicrobial activity and the capability to inhibit biofilms formation of Staphylococcus aureus and Candida albicans. Spectrophotometric investigation of azo compounds release from the polymer matrices confirmed that the materials might have applications in fields where an intrinsic antimicrobial ability of the material is required, such as biomedical tools, biodegradable antibacterial coatings, and films for active packaging. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42357.     

Evaluation of some eco‐friendly plasticizers for PLA films processing

This study was conducted as a first step in order to obtain green materials for food packaging by using an eco‐friendly bioplastic, polylactic acid (PLA), and nontoxic plasticizers. Different types of nontoxic biocompatible plasticizers/lubricants, both obtained in the laboratory, as well as commercial ones, were employed to modulate physical and mechanical properties of PLA. Melt compounding by means of a Brabender mixer led to obtaining of homogeneous materials. The incorporation of PLA oligomer, l ‐lactide, poly(ethylene glycol), and epoxidized soybean oil (USE) improved the melt flow and processability, increasing the hydrophilicity of the resulted plasticized PLA systems. USE significantly increased the elongation at break, reduced the glass transition temperature, and increased the PLA chain mobility. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43223.     

New multifunctional poly(lactide acid) composites: Mechanical,antibacterial, and degradation properties

The aim of this work was to study the effect of the innovative combination of microcrystalline cellulose (MCC) and silver nanoparticles (Ag) on the poly (lactide acid) (PLA) composite properties, to modulate the PLA mechanical response and induce an antibacterial effect. The preparation and characterization of PLA‐based composites with MCC and Ag nanoparticles by twin‐screw extrusion followed by injection molding is reported. A film procedure was also performed to obtain PLA and PLA composite films with a thickness ranged between 20 and 60 μm. The analysis of disintegrability in composting conditions by means of visual, morphological, thermal, and chemical investigations was done to gain insights into the post‐use degradation processes. Tensile test demonstrated the MCC reinforcing effect, while a bactericidal activity of silver‐based composites against a Gram‐negative bacteria (Escherichia coli) and a Gram‐positive bacteria (Staphylococcus aureus) was detected at any time points and temperatures analyzed. Moreover, the disintegrability in composting showed that MCC is able to promote the degradation process. The combination of MCC and Ag nanoparticles in PLA polymer matrix offers promising perspectives to realize multifunctional ternary composites with good mechanical response and antibacterial effect, maintaining the optical transparency and the disintegrability, hence suitable for packaging applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Engineering of Poly Lactic Acids (PLAs) for melt processing: Material structure and thermal properties

Bottles and other packaging account for approximately 70% of the global market of biopolymers, which include both biodegradable and durable materials. Durable materials account for the vast majority of the market, especially the bottles. Degradable polymers are instead refrained by the often‐insufficient mechanical and thermal properties, which limit their usage to single‐use packaging items at ambient temperature and in dry conditions. In this respect, the present work deals with the development and manufacturing of innovative and custom‐built Poly Lactic Acids (PLAs) for injection and compression molding, which are designed to be compostable, suitable for food contact and characterized by a good compromise of mechanical properties and thermal stability. A commercial grade PLA was, therefore, compounded in a twin‐screw co‐rotating extruder by the addition of maleated and glycidyl methacrylate PLAs as chain extenders and micro‐lamellar talc as mineral filler and nucleation promoter. Compatibilization between PLA, chain extenders and mineral filler was, therefore, investigated. Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) were performed to evaluate the material structure and thermal response of the pellets after reactive compounding extrusion. The experimental findings show that material structure and, especially, crystallization of the PLA can be controlled by fine‐tuning the compound formulation as well as by setting of the operational parameters. In addition, achievement of the appropriate crystallization degree in the polymer is found to lead to composite materials, which can boast very good thermal stability. Accordingly, the custom‐built PLA formulations feature the potential to expand significantly the fields of application of non‐durable polymers, thus posing a valid alternative to both durable biopolymers and conventional plastics in injection and compression molding process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44504.     

Structural characterization and antimicrobial activity of chitosan (CS‐40)/nisin complexes

A complex of chitosan (CS‐40) and nisin (CS‐40/nisin) was prepared and characterized with Fourier transform infrared spectroscopy and thermal analysis (thermogravimetry, differential thermogravimetry, and differential scanning calorimetry). The results show that the complex formed mainly by electrostatic interaction between the protonated amino group in CS‐40 backbone with the carboxylate ion of nisin. Minimum inhibitory concentrations (MICs) were evaluated against Gram‐positive bacteria (Staphylococcus aureus, Bacillus subtilis, and Bacillus stearothermophilus), Gram‐negative bacteria (Escherichia coli, Salmonella enteritidis, and Proteus vulgaris), and fungi (Fusarium oxysporum). The results show that the CS‐40/nisin solution did inhibit or even more strongly inhibited the growth of all the tested microorganisms, whereas CS‐40 did not inhibit the growth of F. oxysporum and nisin did not inhibit the growth of Gram‐negative bacteria (E. coli, S. enteritidis, and P. vulgaris). The relative inhibition times of CS‐40/nisin solutions with different concentrations and ratios of CS‐40 and nisin were also investigated against the seven microorganisms. The results showed that CS‐40/nisin solutions with CS‐40/nisin concentration ratios of 0.05/0.005, 0.05/0.0025, 0.05/0.00125, and 0.025/0.0001% had higher antimicrobial activity against all tested bacteria and fungi. The relationship between complex formation and antimicrobial activity is discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of polymer swelling and dissolution into food simulants on the release of graphene nanoplates and carbon nanotubes from poly(lactic) acid and polypropylene composite films

The study compared the effects of swelling and dissolution of a matrix polymer by food simulants on the release of graphene nanoplates (GNPs) and multiwall carbon nanotubes (MWCNTs) from poly(lactic) acid (PLA) and polypropylene (PP) composite films. The total migration was determined gravimetrically in the ethanol and acetic acid food simulants at different time and temperature conditions, while migrants were detected by laser diffraction analysis and transmission electron microscopy. Swelling, thermal analysis, and scanning electron microscopy were applied to characterize the degradation of polymer films at the migration conditions. The release of nanoparticles was found in a high‐temperature migration test of 4 h at 90 °C. The hydrolytic dissolution of the PLA polymer in the food simulants caused a migration of GNPs (>100 nm) from the PLA/GNP/MWCNT films into the simulant solvents, while the entangled MWCNTs formed a network on the film surface, preventing their migration from the PLA composite films. In contrast, the PP polymer slightly swells in ethanol solvents, allowing some short carbon nanotubes to be released from the surface and cut edges of the PP/MWCNT film into food simulants. Mathematical modeling of diffusion was applied that accounts for type of polymer, time–temperature conditions, and solvent concentration; model parameters were validated with experimental results. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45469.     

Preparation,characterization, and biodegradability of renewable resource‐based composites from recycled polylactide bioplastic and sisal fibers

The biodegradability, morphology, and mechanical thermal properties of composite materials composed of polylactide (PLA) and sisal fibers (SFs) were evaluated. Composites containing acrylic acid‐grafted PLA (PLA‐g‐AA/SF) exhibited noticeably superior mechanical properties because of greater compatibility between the two components. The dispersion of SF in the PLA‐g‐AA matrix was highly homogeneous as a result of ester formation and the consequent creation of branched and crosslinked macromolecules between the carboxyl groups of PLA‐g‐AA and hydroxyl groups in SF. Furthermore, with a lower melt temperature, the PLA‐g‐AA/SF composite is more readily processed than PLA/SF. Both composites were buried in soil to assess biodegradability. Both the PLA and the PLA‐g‐AA/SF composite films were eventually completely degraded, and severe disruption of film structure was observed after 6–10 weeks of incubation. Although the degree of weight loss after burial indicated that both materials were biodegradable even with high levels of SF, the higher water resistance of PLA‐g‐AA/SF films indicates that they were more biodegradable than those made of PLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of antistatic packaging for electronic components based on poly(lactic acid)/carbon black composites

Poly(lactic acid) (PLA) is a biodegradable aliphatic polymer obtained from renewable sources; its main application is in the packaging sector. Electronic components require the use of antistatic packaging that prevents damage and electric shock. As PLA has no conductive characteristics, it requires the addition of allotropic carbon forms such as conductive carbon black to make the polymer less resistive as the dissipative material and making it suitable for the manufacture of antistatic packaging. In this study, PLA was melt blended with 5, 10, and 15 wt % of carbon black. The composites were prepared using a high-speed mixer. Samples were characterized by Izod impact resistance tests, scanning electron microscopy, thermal properties, electrical characterization, and biodegradation tests in garden soil. The addition of carbon black in the PLA matrix increases the temperature of degradation and decreases the crystallinity degree and the impact resistance of the composites. However, carbon black is a great option to increase the electrical conductivity of PLA. The addition of carbon black in PLA makes the composite less resistive and suitable for use as antistatic packaging for the transportation and storage of electronic components. Furthermore, this composite does not cause damage to the environment as the carbon black does not interfere in the degradation mechanism of PLA. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47273.     

Thermal and mechanical properties of plasticized poly(L‐lactide) nanocomposites with organo‐modified montmorillonites

Nanocomposites of poly(lactide) (PLA) and the PLA plasticized with diglycerine tetraacetate (PL‐710) and ethylene glycol oligomer containing organo‐modified montmorillonites (ODA‐M and PGS‐M) by the protonated ammonium cations of octadecylamine and poly(ethylene glycol) stearylamine were prepared by melt intercalation method. In the X‐ray diffraction analysis, the PLA/ODA‐M and plasticized PLA/ODA‐M composites showed a clear enlargement of the difference of interlayer spacing between the composite and clay itself, indicating the formation of intercalated nanocomposite. However, a little enlargement of the interlayer spacing was observed for the PLA/PGS‐M and plasticized PLA/PGS‐M composites. From morphological studies using transmission electron microscopy, a finer dispersion of clay was observed for PLA/ODA‐M composite than PLA/PGS‐M composite and all the composites using the plasticized PLA. The PLA and PLA/PL‐710 composites containing ODA‐M showed a higher tensile strength and modulus than the corresponding composites with PGS‐M. The PLA/PL‐710 (10 wt %) composite containing ODA‐M showed considerably higher elongation at break than the pristine plasticized PLA, and had a comparable tensile modulus to pure PLA. The glass transition temperature (T_g) of the composites decreased with increasing plasticizer. The addition of the clays did not cause a significant increase of T_g. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Development of poly(lactic acid) films with propolis as a source of active compounds: Biodegradability,physical, and functional properties

Active films (AFs) using poly(lactic acid) (PLA) as a polymeric matrix containing various propolis concentrations (5, 8.5, and 13%) as the active agent (AA) were developed using a casting method. The purpose was to determine the effects of the incorporation of AA on the physical properties of the films and to evaluate the antioxidant and antimicrobial activities. Tensile strength and elastic modulus of the AFs decreased relative to the control (PLA without AA). Introducing the active substances from propolis into the PLA also affected its thermal properties (glass transition). Adding AAs to the polymer generated more opacity with a green-yellowish color compared to the control. In addition, AFs exhibited reduced water vapor permeability as the AA concentration increased. Biodegradation assay showed that the AFs degraded faster than the control. AFs exhibited antioxidant activity, which was measured as the ability to scavenge free radicals (2,2-diphenyl-1-picrylhydrazyl and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate)), due to the presence of bioactive compounds (phenolics). Antimicrobial activity was evaluated against Escherichia coli and showed a reduction over 4-log cycles. Therefore, incorporation of propolis is a useful strategy for the development of active packaging with antioxidant and antimicrobial effects, which increase the shelf life of food products. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47090.     

Synthesis,phase behaviors,and mechanical properties of biphenyl‐type epoxy resins and composites

Diglycidyl ether of 3,3′,5,5′‐tetramethyl‐4,4′‐biphenyl (TMBPDGE) which has been found great applications in semiconductor packaging was synthesized. The liquid crystalline phases of diglycidyl ether of 4,4′‐dihydroxybiphenol (BPDGE) cured with phenol novolac (PN) were studied by wide angle X‐ray diffraction (WAXD) and polarized optical microscopy (POM). BPDGE was in situ copolymerized with TMBPDGE to improve its thermal and mechanical properties by means of the LC domains retained in the crosslinked networks. The results indicated that a nematic phase was formed and fixed with proper curing schedule when BPDGE was cured with PN that had no neighboring active hydrogens and the LC domains could also be efficiently embedded into the composite systems. Dynamic mechanical properties showed that epoxy networks containing LC domains displayed higher α‐relaxation temperature and linear elastic modulus traces. The impact toughness and T_g were improved with the addition of BPDGE. Scanning electron microscope observation of the fracture surfaces showed that there was a change in failure mechanism in the composite systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007