Addition of α‐tocopherol on poly(lactic acid): Thermal,mechanical, and sorption properties

This work investigates the effect of the addition of a well‐known antioxidant, α‐tocopherol in poly (lactic acid) flexural and barrier properties. For that purpose, films of poly(lactic acid) enriched with 0, 2.2, and 4.4% of α‐tocopherol were prepared. Differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis were used to characterize the changes in the mechanical and thermal properties. The sorption of oxygen and carbon dioxide in the prepared enriched films of poly(lactic acid) was measured at different temperatures between 283 and 313 K and pressures up to atmospheric pressure using a Quartz Crystal Microbalance. Although no significant changes were found in the mechanical and thermal properties, the addition of α‐tocopherol promotes an increasing in the oxygen sorption and the convex shape of the isotherms indicate a strong interaction gas‐polymer. Regarding the sorption of carbon dioxide, no pronounced effect was found. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymer processing and characterization of LLDPE films loaded with α‐tocopherol,quercetin, and their cyclodextrin inclusion complexes

Natural antioxidant additives were compounded into linear low‐density polyethylene (LLDPE) using a twin‐screw counter‐rotating mixer and compression molded into films. Manufactured LLDPE films contained 2715 mg kg^?1 α‐tocopherol in its free and β‐cyclodextrin complexed form and 1950 mg kg^?1 quercetin in its free and γ‐cyclodextrin complexed form. Both cyclodextrin complexes were loaded into films at 1.5% by weight. These natural antioxidants were incorporated into LLDPE resins with two different catalyst types, Ziegler‐Natta and metallocene. Films were characterized by optical microscopy, oxidation induction time (OIT), oxygen transmission rate, contact angle analysis, and atomic force microscopy (AFM). All antioxidant additives increased the oxidative stability of LLDPE as measured by increased OIT, particularly quercetin. Natural antioxidants and their cyclodextrin inclusion complexes may provide a dual function in packaging to protect the polymer from oxidative degradation during melt processing and to delay the onset of oxidation of the packaged food during storage. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystallization behavior and isothermal crystallization kinetics of PLLA blended with ionic liquid, 1‐butyl‐3‐methylimidazolium dibutylphosphate

The crystallization behavior and isothermal crystallization kinetics of neat poly(l ‐lactic acid) (PLLA) and PLLA blended with ionic liquid (IL), 1‐butyl‐3‐methylimidazolium dibutylphosphate, were researched by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X‐ray diffraction (WXRD). Similar to the non‐isothermal crystallization behavior of neat PLLA, when PLLA melt was cooled from 200 to 20°C at a cooling rate of 10°C min^?1, no crystallization peak was detected yet with the incorporation of IL. However, the glass transition temperature and cold crystallization temperature of PLLA gradually decreased with the increase of IL content. It can be attributed to the significant plasticizing effect of IL, which improved the chain mobility and cold crystallization ability of PLLA. Isothermal crystallization kinetics was also analyzed by DSC and described by Avrami equation. For neat PLLA and IL/PLLA blends, the Avrami exponent n was almost in the range of 2.5–3.0. It is found that t_1/2 reduced largely, and the crystallization rate constant k increased exponentially with the incorporation of IL. These results show that the IL could accelerate the overall crystallization rate of PLLA due to its plasticizing effect. In addition, the dependences of crystallization rate on crystallization temperature and IL content were discussed in detail according to the results obtained by DSC and POM measurements. It was verified by WXRD that the addition of IL could not change the crystal structure of PLLA matrix. All samples isothermally crystallized at 100°C formed the α‐form crystal. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41308.     

γ‐ and δ‐tocopherols are more effective than α‐tocopherol on the autoxidation of a 10% rapeseed oil triacylglycerol‐in‐water emulsion with and without a radical initiator

The antioxidative effects of γ‐ and mainly δ‐tocopherol in a multiphase system were hardly considered up to now. The aim of this study was i) to assess the effects and ii) to follow the degradation of α‐, γ‐ and δ‐tocopherol in concentrations of 0.01%, 0.05%, 0.1% and 0.25% during the oxidation of a 10% purified rapeseed oil triacylglycerol‐in‐water emulsion at 40 °C in the dark for 15 wk in a system containing a low oxygen concentration. Oxidation experiments were performed weekly by assessing the formation of hydroperoxides and hexanal, and the stability of the tocopherols was determined using high‐performance liquid chromatography. Storage tests were conducted with and without the addition of 0.01% α, α′‐azoisobutyronitrile (AIBN), which is a known radical initiator. α‐Tocopherol increased the formation of hydroperoxides in both tests as well as the generation of hexanal when the radical initiator was added; furthermore it was the least stable. γ‐Tocopherol delayed the formation of hexanal and prolonged the stability of the emulsion in a dose‐dependant manner. δ‐Tocopherol was the most stable and also the most effective in delaying lipid oxidation in the emulsions. Each concentration that was tested reduced the rate of hydroperoxide and especially hexanal formation. Hexanal was only formed to a slight extent after 15 wk of oxidation in the test with AIBN and the lowest dose of 0.01% δ‐tocopherol. For all tocopherols, strong correlations were found between tocopherol stability and the extent of oxidation. Results suggest that i) mainly δ‐tocopherol, but also γ‐tocopherol even less pronounced, are very good antioxidants in order to stabilize and prolong the shelf life of oil‐in‐water emulsions, ii) the antioxidative effects were intensified with increasing amounts.     

Poly(L‐lactic acid) metal organic framework composites: optical,thermal and mechanical properties

Biodegradable composites based on poly(L ‐lactic acid) (PLLA) and metal organic frameworks (MOFs) were developed. PLLA without and with the addition of 1, 3 and 5 wt% MOFs was melt compounded in a microextruder. The optical, physical, thermal, mechanical and thermomechanical properties of the composites were evaluated. The Fourier transform infrared, ultraviolet and colorimetric studies showed selected absorption at particular wavelengths due to the presence of copper and benzene belonging to the MOFs. The dynamic mechanical analysis results revealed that the heat deflection temperature, storage modulus and loss modulus of the PLLA–MOF composites did not significantly change compared with the neat PLLA samples. However, a significant decrease in the brittleness of the PLLA–MOF composite was found as evidenced by an increase of 15% in Izod impact strength and 170% in elongation at break. Overall, the brittleness of the PLLA–MOF composite sample decreased as the amount of MOF in the PLLA increased. Copyright © 2011 Society of Chemical Industry     

An investigation of the effect of silane water‐crosslinking on the properties of poly(L‐lactide)

A silane‐grafting water‐crosslinking approach was developed to crosslink poly(L ‐lactide) (PLLA) by grafting vinylalkoxysilane onto PLLA using dicumyl peroxide, followed by silane hydrolysis to form siloxane linkages between PLLA chains. The degree of silane grafting onto PLLA was qualitatively characterized using Fourier transform infrared spectroscopy and quantitatively determined using inductively coupled plasma mass spectrometry. Crosslinked PLLA films were obtained by curing of silane‐grafted PLLA in hot water. Gel fractions were evaluated in order to calculate the crosslinking reaction kinetics and crosslinking density. Various techniques were used to investigate the effect of silane water‐crosslinking on the thermomechanical properties, hydrolysis resistance and biodegradation of PLLA. In addition to an improvement in thermal stability and mechanical properties, hydrolysis resistance was significantly enhanced as a result of silane water‐crosslinking of PLLA. Moreover, the biodegradation of silane water‐crosslinked PLLA was retarded compared with neat PLLA. Copyright © 2010 Society of Chemical Industry     

Process efficiency and long‐term performance of α‐tocopherol in film‐blown linear low‐density polyethylene

α‐Tocopherol was compared with a commercial phenolic antioxidant (Irganox 1076) as a long‐term and process antioxidant in film‐blown and compression‐molded linear low‐density polyethylene. The antioxidant function of α‐tocopherol was high in the film‐blown material, especially in the processing, according to oxygen induction time measurements with differential scanning calorimetry. The residual content of α‐tocopherol after processing, determined with chromatographic techniques, was less than that of the commercial phenolic antioxidant in both the film‐blown and compression‐molded materials. The process stabilizing efficiency was nevertheless higher for the material containing α‐tocopherol. During the long‐term stabilization, the efficiency of α‐tocopherol was less than that of the commercial phenolic stabilizer Irganox 1076 in the thin films, according to chemiluminescence and infrared measurements. The long‐term efficiency in the compression‐molded samples stabilized with α‐tocopherol or Irganox 1076 was equally good because of the low loss of both α‐tocopherol and Irganox 1076 from the thicker films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2427–2439, 2005     

Characterization of the mechanical and thermal properties and morphological behavior of biodegradable poly(L‐lactide)/poly(ε‐caprolactone) and poly(L‐lactide)/poly(butylene succinate‐co‐L‐lactate) polymeric blends

Two series of biodegradable polymer blends were prepared from combinations of poly(L ‐lactide) (PLLA) with poly(?‐caprolactone) (PCL) and poly(butylene succinate‐co‐L ‐lactate) (PBSL) in proportions of 100/0, 90/10, 80/20, and 70/30 (based on the weight percentage). Their mechanical properties were investigated and related to their morphologies. The thermal properties, Fourier transform infrared spectroscopy, and melt flow index analysis of the binary blends and virgin polymers were then evaluated. The addition of PCL and PBSL to PLLA reduced the tensile strength and Young's modulus, whereas the elongation at break and melt flow index increased. The stress–strain curve showed that the blending of PLLA with ductile PCL and PBSL improved the toughness and increased the thermal stability of the blended polymers. A morphological analysis of the PLLA and the PLLA blends revealed that all the PLLA/PCL and PLLA/PBSL blends were immiscible with the PCL and PBSL phases finely dispersed in the PLLA‐rich phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of multi‐branched PDLA additives on the mechanical and thermomechanical properties of blends with PLLA

Stereocomplex formation between poly(l ‐lactic acid) (PLLA) and poly(d ‐lactic acid) (PDLA) in the melt state was investigated and altered via the addition of multi‐branched poly(d ‐lactide) (PDLA) additives. Two different multi‐branched PDLA additives, a 3‐arm and 4‐arm star‐shaped polymeric structure, were synthesized as potential heat resistance modifiers and incorporated into PLLA at 5, 10, and 20 (w/w) through melt blending. Mechanical and thermomechanical properties of these blends were compared with linear poly(l ‐lactide) (PLLA) as well as with blends formed by the addition of two linear PDLA analogs that had similar molecular weights to their branched counterparts. Blends with linear PDLA additives exhibited two distinct melting peaks at 170–180°C and 200–250°C which implied that two distinct crystalline domains were present, that of the homopolymer and that of the stereocomplex, the more stable crystalline structure formed by the co‐crystallization of both d ‐ and l ‐lactide enantiomers. In contrast, blends of PLLA with multi‐branched PDLA formed a single broad melting peak indicative of mainly formation of the stereocomplex, behavior which was confirmed by X‐ray diffraction (XRD) analysis. The heat deflection temperature determined by thermal mechanical analysis was improved for all blends compared to neat PLLA, with increases of up to180°C for 20% addition of the 3‐arm PLLA additive. Rheological properties of the blends, as characterized by complex viscosity (η*), remained stable over a wide temperature range. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42858.     

Synthesis and characterization of melt‐processable polyimides derived from 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene

A series of molecular‐weight‐controlled imide resins end‐capped with phenylethynyl groups were prepared through the polycondensation of a mixture of 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene and 1,3‐bis(4‐aminophenoxy)benzene with 4,4′‐oxydiphthalic anhydride in the presence of 4‐phenylethynylphthalic anhydride as an end‐capping agent. The effects of the resin chemical structures and molecular weights on their melt processability and thermal properties were systematically investigated. The experimental results demonstrated that the molecular‐weight‐controlled imide resins exhibited not only meltability and melt stability but also low melt viscosity and high fluidability at temperatures lower than 280°C. The molecular‐weight‐controlled imide resins could be thermally cured at 371°C to yield thermoset polyimides by polymer chain extension and crosslinking. The neat thermoset polyimides showed excellent thermal stability, with an initial thermal decomposition temperature of more than 500°C and high glass‐transition temperatures greater than 290°C, and good mechanical properties, with flexural strengths in the range of 140.1–163.6 MPa, flexural moduli of 3.0–3.6 GPa, tensile strengths of 60.7–93.8 MPa, and elongations at break as high as 14.7%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Morphology,mechanical properties,and thermal stability of poly(L‐lactic acid)/poly(butylene succinate‐co‐adipate)/silicon dioxide composites

Poly(butylene succinate‐co‐adipate) (PBSA) and two types of SiO₂ (hydrophilic or hydrophobic) were used to modify poly(L ‐lactic acid) (PLLA). The mechanical properties, rheological and thermal behavior, phase morphology, and thermal stability of PLLA/PBSA/SiO₂ composites were investigated. The impact strength, flexural strength, and modulus of PLLA/PBSA blends increased after the addition of hydrophobic SiO₂ without decreasing the elongation at break, and the elongation at break monotonically decreased with increasing hydrophilic SiO₂ content. The melt elasticity and viscosity of the PLLA/PBSA blend increased with the addition of SiO₂. The hydrophilic SiO₂ was encapsulated by the dispersed PBSA phase in the composites, which led to the formation of a core–shell structure, whereas the hydrophobic SiO₂ was more uniformly dispersed and mainly located in the PLLA matrix, which was desirable for the optimum reinforcement of the PLLA/PBSA blend. The thermogravimetric analysis results show that the addition of the two types of SiO₂ increased the initial decomposition temperature and activation energy and consequently retarded the thermal degradation of PLLA/PBSA. The retardation of degradation was prominent with the addition of hydrophobic SiO₂. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reactive compatibilization of poly(l‐lactic acid)/poly(propylene carbonate) blends: Thermal,thermomechanical, and morphological properties

Poly(l ‐lactic acid) (PLLA) was blended with poly(propylene carbonate) (PPC) with various compositions by a melt‐blending process to evaluate their general properties for a potential flexible packaging field. The mechanical properties, including the tensile strength and modulus, revealed a tendency to decrease with the addition of ductile PPC; this was induced by the poor interfacial adhesion between PLLA and PPC with the cavities and clear edges and was observed through morphological observation. Reactive compatibilization was applied to improve the interfacial adhesion between PLLA and PPC, and the elongation at break was profoundly enhanced because of the improved interfacial adhesion between the two phases. The compatibilized PLLA/PPC blends showed considerable improvements in the storage modulus in the transition region with stable thermal stability; this could be a benefit for thermal processing. The addition of PPC had a great effect on the solidlike behavior and increased the elasticity of the PLLA/PPC blends. Up to 2.0 phr maleic anhydride showed a great efficiency in enhancing the dynamic storage modulus and complex viscosity of the PLLA/PPC blends. We also confirmed that it was feasible to fabricate PLLA/PPC blends with controllable barrier properties with combination of PLLA and PPC under reactive compatibilization while retaining the biodegradability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43388.     

Part 7. Effects of poly(L‐lactide‐co‐ϵ‐caprolactone) on morphology,structure, crystallization,and physical properties of blends of poly(L‐lactide) and poly(ϵ‐caprolactone)

Blended films of poly(L ‐lactide) [ie poly(L ‐lactic acid)] (PLLA) and poly(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐caprolactone) (PLLA‐CL) were prepared by solution‐casting. The effects of PLLA‐CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA‐CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross‐section of the PLLA/PCL blend film. The melting temperatures (T_m) of PLLA and PCL in the films remained unchanged upon addition of PLLA‐CL, while the crystallinities of PLLA and PCL increased at PLLA contents [X_PLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4–0.7 and at most of the X_PLLA values, respectively. The addition of PLLA‐CL improved the tensile strength and the Young modulus of the films at X_PLLA of 0.5–0.8 and of 0–0.1 and 0.5–0.8, respectively, and the elongation at break of the films at all the X_PLLA values. These findings strongly suggest that PLLA‐CL was miscible with PLLA and PCL, and that the dissolved PLLA‐CL in PLLA‐rich and PCL‐rich phases increased the compatibility between these two phases. © 2003 Society of Chemical Industry     

Thermal degradation behaviour of multi‐walled carbon nanotube‐reinforced poly(L‐lactide) nanocomposites

BACKGROUND: Polymer/multi‐walled carbon nanotube (MWCNT) composites are one of the most promising alternatives to conventional polymer composites filled with micrometre‐sized fillers. This approach can also be applied for the improvement of mechanical properties and thermal stability of biodegradable aliphatic polyesters, such as poly(L ‐lactide) (PLLA), which have been receiving increasing attention due to environmental concerns. Thermal degradation behaviour provides useful information for the determination of the optimum processing conditions and for identification of potential applications of final products. RESULTS: The PLLA/MWCNT composites investigated showed a higher thermal degradation peak temperature and onset temperature of degradation along with a higher amount of residue at the completion of degradation than neat PLLA. Moreover, PLLA/MWCNT composites with a greater MWCNT content showed higher activation energy of thermal degradation than those with a lower MWCNT loading, which confirmed the positive effect of MWCNT incorporation on the enhancement of PLLA thermal stability. CONCLUSION: This study explored the thermal degradation behaviour of PLLA/MWCNT composites by observing the weight loss, molecular weight and mechanical properties during non‐isothermal and isothermal degradation. The incorporation of MWCNTs into the PLLA matrix enhanced considerably the mechanical properties and thermal stability. Copyright © 2009 Society of Chemical Industry     

Kinetics of antioxidant action of α‐ and γ‐toco‐pherols in sunflower and soybean triacylglycerols

A kinetic analysis was performed to evaluate the antioxidant behavior of α‐ and γ‐to‐copherols (5—2000 ppm) in purified triacylglycerols obtained from sunflower oil (TGSO) and soybean oil (TGSBO) at 100 °C. Different kinetic parameters were determined, viz. the stabilization factor as a measure of effectiveness, the oxidation rate ratio as a measure of strength, and the antioxidant activity which combines the other two parameters. In the low concentration range (up to 400 ppm in TGSBO and up to 700 ppm in TGSO) α‐tocopherol was a more active antioxidant than γ‐tocopherol whereas the latter was more active at higher concentrations. It has been found that the different activity of the tocopherols is not due to their participation in chain initiation reactions, but that the loss of antioxidant activity at high tocopherol concentrations is due to their consumption in side reactions. The rates of these reactions are higher in TGSBO than in TGSO. Both α‐tocopherol itself and its radicals participated more readily in side reactions than γ‐tocopherol and its radicals. Both α‐ and γ‐tocopherol reduce lipid hydroperoxides, thus generating alkoxyl radicals which are able to amplify the rate of lipid oxidation by participating in chain propagation reactions.     

Physical properties and enzymatic hydrolysis of poly(L‐lactide)–TiO2 composites

Amorphous poly(L ‐lactide) (PLLA) composite films with titanium dioxide (TiO₂) particles were prepared by solution‐casting using methylene chloride as a solvent, followed by quenching from the melt. The effects of surface treatment, volume fraction, size, and crystalline type of the TiO₂ particles on the mechanical properties and enzymatic hydrolysis of the composite films were investigated. The tensile strength of the PLLA composite films containing TiO₂ particles except for anatase‐type ones with a mean particle size of 0.3–0.5 μm was lowered and the Young's modulus became higher with increasing the content of TiO₂ particles. The tensile strength of the composite films containing anatase‐type TiO₂ with a mean particle size of 0.3–0.5 μm at contents of 20 wt % or less was almost the same as that of the pure PLLA film. The enzymatic hydrolysis of PLLA matrix was accelerated by the addition of the hydrophilic anatase‐type TiO₂ particles (nontreated or Al₂O₃ treated) with a mean particle size of 0.3–0.5 μm at relatively high contents such as 20 wt %. On the other hand, the enzymatic hydrolysis of PLLA matrix was inhibited by composite formation with the hydrophobic rutile‐type TiO₂ particles (Al₂O₃‐stearic acid treated, or ZrO₂‐Al₂O₃‐stearic acid treated). These results suggest that the mechanical properties and enzymatic hydrolyzability of the PLLA can be controlled by the kind and amount of the added TiO₂ particles. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 190–199, 2005     

α‐, γ‐ and δ‐ Tocopherols as inhibitors of isomerization and decomposition of cis,trans methyl linoleate hydroperoxides

The effects of α‐, γ‐ and δ‐tocopherols on the stability and decomposition reactions of lipid hydroperoxides were studied. Isomerization and decomposition of cis,trans methyl linoleate hydroperoxides (cis,trans ML‐OOH) in hexadecane at 40 °C were followed by high‐performance liquid chromatography. Due to its higher hydrogen donating ability, α‐tocopherol was more efficient than γ‐ and δ‐tocopherols in inhibiting the isomerization of cis,trans ML‐OOH to trans,trans ML‐OOH. α‐Tocopherol stabilized hydroperoxides into the cis,trans configuration, whereas γ‐ and δ‐tocopherols allowed hydroperoxides to convert into trans,trans isomers. Thus, the biological importance of α‐tocopherol as compared to other tocopherols may be partly due to its better efficacy in protecting the cis,trans configuration of hydroperoxides formed, for example, in the enzymatic oxidation of polyunsaturated fatty acids. The isomeric configuration of hydroperoxides has an impact on biological activities of further oxidation products of polyunsaturated fatty acids. Paradoxically, the order of activity of tocopherols with regard to hydroperoxide decomposition was different from that obtained for hydroperoxide isomerization. γ‐ and δ‐tocopherols were more efficient inhibitors of ML‐OOH decomposition when compared to α‐tocopherol. A loss of antioxidant efficiency, observed as the tocopherol concentration increased from 2 to 20 mM, was highest for α‐tocopherol but was also evident for γ‐ and δ‐tocopherols. Thus, the differences in the relative effects of tocopherols at differing concentrations seem to result from a compromise between their radical scavenging efficiency and participation in side reactions of peroxidizing nature.     

Antioxidant and prooxidant effects of α‐tocopherol in a linoleic acid‐copper(II)‐ascorbate system

The peroxidation of linoleic acid (LA) in the absence and presence of either Cu(II) ions alone or Cu(II)‐ascorbate combination was investigated in aerated and incubated emulsions at 37°C and pH 7. LA peroxidation induced by either copper(II) or copper(II)‐ascorbic acid system followed pseudo‐first order kinetics with respect to primary (hydroperoxides) and secondary (aldehydes‐ and ketones‐like) oxidation products, detected by ferric‐thiocyanate and TBARS tests, respectively. α‐Tocopherol showed both antioxidant and prooxidant effects depending on concentration and also on the simultaneous presence of Cu(II) and ascorbate. Copper(II)‐ascorbate combinations generally led to distinct antioxidant behavior at low concentrations of α‐tocopherol and slight prooxidant behavior at high concentrations of α‐tocopherol, probably associated with the recycling of tocopherol by ascorbate through reaction with tocopheroxyl radical, while the scavenging effect of α‐tocopherol on lipid peroxidation was maintained as long as ascorbate was present. On the other hand, in Cu(II) solutions without ascorbate, the antioxidant behavior of tocopherol required higher concentrations of this compound because there was no ascorbate to regenerate it. Practical applications: Linoleic acid (LA) peroxidation induced by either copper(II) or copper(II)‐ascorbic acid system followed pseudo‐first order kinetics with respect to primary (hydroperoxides) and secondary (e.g., aldehydes and ketones) oxidation products. α‐Tocopherol showed both antioxidant and prooxidant effects depending on concentration and also on the simultaneous presence of Cu(II) and ascorbate. The findings of this study are believed to be useful to better understand the actual role of α‐tocopherol in the preservation of heterogenous food samples such as lipid emulsions. Since α‐tocopherol (vitamin E) is considered to be physiologically the most important lipid‐soluble chain‐breaking antioxidant of human cell membranes, the results can be extended to in vivo protection of lipid oxidation.     

Synergistic effect of α‐ZrP and graphene oxide nanofillers on the gas barrier properties of PVA films

Two types of 2D nanofillers, α‐zirconium phosphate (α‐ZrP) and graphene oxide (GO), were synthesized and incorporated into poly(vinyl alcohol) (PVA) with 1 wt % loading level at various α‐ZrP:GO (Z:G = 5:1, 2:1, 1:1, 1:2, and 1:5) ratios. The resulting nanocomposites were tested for barrier properties by casting films from solution. The structure and morphology of α‐ZrP and GO were characterized by Fourier‐transform infrared spectroscopy, atomic force microscope, scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction, which demonstrated successful preparation of exfoliated α‐ZrP and GO. The physical characteristics of the nanocomposite films, including thermal, mechanical, and gas barrier properties were investigated. The results indicated that the tensile strength, Young's modulus, and elongation at break of the PVA nanocomposite films with Z:G hybrid nanofiller improved compared to neat PVA. The glass transition temperature, melting temperature, and crystallinity also increased. Consequently there appears to be a synergistic effect with these two types of nanofillers that formed a specific macro structure of a “wall.” This macrostructure resulted in excellent O₂ gas barrier properties with the PVA/Z:G‐5:1 nanocomposite films having the best performance. The of the PVA/Z:G‐5:1 nanocomposite decreased from 1.835 × 10^?16 to 0.587 × 10^?16 cm³ cm cm^?2 s^?1 Pa^?1 compared with neat PVA. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46455.     

Preparation and properties of castor oil‐based polyurethane/α‐zirconium phosphate composite films

Novel castor oil‐based polyurethane/α‐zirconium phosphate (PU/α‐ZrP) composite films with different α‐ZrP loading (0–1.6 wt %) and different NCO/OH molar ratios were synthesized by a solution casting method. The characteristic properties of the PU/α‐ZrP composite films were examined by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile testing. The results from Fourier transform infrared spectroscopy indicated that strong intermolecular hydrogen bonding formed between α‐ZrP and PU, XRD and SEM results revealed that the α‐ZrP particles were uniformly distributed in the PU matrix at low loading, and obvious aggregation existed at high loading. Because of hydrogen bonding interactions, the maximum values of tensile strength were obtained with 0.6 wt % α‐ZrP loading and 1.5 of NCO/OH molar ratio in the matrix. Evidence proved that the induced α‐ZrP used as a new filler material can affect considerably the mechanical and thermal properties of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011