Degradation of low density polyethylene during extrusion. IV. Off‐flavor compounds in extruded films of stabilized LDPE

This study was aimed at finding a correlation between the experienced off‐flavor in packed foods and the presence of specific degradation products in LDPE packaging films. The possibility to trap degradation products by chemical reactions with scavengers, i.e., a zeolite additive or antioxidants, was investigated This would prevent degradation products from migrating to the polymer film surface and further into food in contact with the film. It was found that off‐flavor noted in water packed in LDPE films depended on extrusion temperature and exposure time for the melt to oxygen, that is, the parameters that influence the contents of oxidation products that are able to migrate from the polymer film. It was also found that adsorption of oxidative degradation products in a zeolite additive or protection of LDPE by using antioxidants could prevent off‐flavor in the packed product (water). However, the antioxidant should be selected with regard to extrusion temperature because thermal instability in the additive might jeopardize the intended effect. Multifunctional antioxidants seem to provide improved protection, the most effective one evaluated in this work being Irganox E201, i.e., vitamin E. Concentrations of oxidized degradation products are well correlated to the perceived off‐flavor in the packed water. The highest correlation between off‐flavor and oxidized components was found for ketones in the range of C₇ to C₉ and aldehydes in the range of C₆ to C₉. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 583–595, 2005     

Effects of a mixture of stabilizers on the structure and mechanical properties of polyethylene during reprocessing

The properties of two polyethylenes [a high‐density polyethylene (HDPE) and a low‐density polyethylene (LDPE)] were studied after several extrusion cycles. To reduce the degradation effects during the reprocessing, a mixture of two stabilizers was added to the formulations. The predominant degradation mechanism was chain scission for the HDPE and chain branching and crosslinking for the LDPE. For both polyethylenes the FTIR spectra exhibited a growth in the number of carbonyl groups as a function of the number of extrusion cycles. Their tensile properties were degraded with the reprocessing but both polyethylenes maintained their nearly constant thermal behavior and crystallinity. The addition of a primary phenolic antioxidant and a secondary phosphite antioxidant preserved the melt behavior of virgin materials after the reprocessing and reduced the degradation effects. From the tensile tests, the efficiency of the antioxidants in the LDPE was very high and, after the reprocessing, the material retained the mechanical properties of virgin LDPE. The efficiency of the antioxidants for the HDPE was not significant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3910–3916, 2004     

Development of low density polyethylene nanocomposites films for packaging

Requirements for adequate permeability of polymeric materials to gases and vapors, good barrier and mechanical properties of polymers have boosted interest in developing new strategies to improve these properties. Research and development in polymeric materials coupled with appropriate filler, matrix-filler interaction and new formulation strategies to develop composites have potential applications in various types of packaging (agricultural produce, dried food, frozen food etc.). In this study, LDPE composites containing various types of fillers (zeolite TMAZ 7, nanoclay Cloisite 20A and precipitated calcium carbonate, CaCO₃) were prepared using extrusion/injection molding. The microstructural and morphological changes as well as mechanical features of samples were characterized by scanning electronic microscopy and by tensile tests. The thermal degradation of LDPE composites was studied using thermogravimetric analysis. Barrier properties (permeability, the diffusion and the solubility constant) in modified LDPE samples were determined. It is found that used minor clay concentration is already very effective for achievement of good morphology. In the presence of nanoparticles, at lower content, the value of oxygen permeability of LDPE decreases. Also, the results have revealed that the samples containing fillers have increased thermal stability in comparison to pure LDPE.     

Synthesis and performance of phenolic polybutadiene‐bound stabilizers

An antioxidant derivative, 6‐sulfanylhexyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propanoate, was synthesized and examined. With a radical initiator, the addition of this compound to pending vinyls of OH‐telechelic, low molecular weight liquid polybutadiene (LBH) was performed to various degrees of conversion to form polymeric antioxidants (PAOs) in which the phenolic moiety was separated from the main chain by a spacer [? CH₂CH₂? S? (CH₂)₆? O? CO? ]. Pure, unstabilized LBH was mixed in several ratios with PAOs, Irganox 1520, and Irganox 1076, and the oxidation stabilities of these mixtures, determined by thermogravimetric analysis and differential scanning calorimetry, were compared. Probably because of their good compatibility with LBH, PAOs exhibited equal or better effectiveness than commercial antioxidants of the Irganox type. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 885–889, 2003     

Crosslinking of low‐density polyethylene by diisocyanates for superior barrier properties

The chemical modification of low‐density polyethylene (LDPE) resins with hexamethylene diisocyanate and toluene diisocyanate was achieved. The reaction of LDPE with diisocyanate was monitored by Fourier transform infrared spectroscopy, wherein the appearance of new peaks at 3326, 1620, and 1572 cm^?1 corresponding to ? N? H stretching, ? (C?O)? NH₂ stretching, and ? N? H bending in an amide moiety, respectively, was observed. Modified films of excellent clarity and uniform thickness were obtained by the solution casting of crosslinked polyethylene. The oxygen transmission rate (OTR), water vapor transmission rate (WVTR), grease resistance, and thermal properties of the modified films were studied. The results clearly indicate that the OTR was improved by 35% and that grease resistance was improved by 90–125% in the crosslinked LDPE films with little change in their strengths. The heat seal characteristics, however, showed that relatively higher temperatures were needed to achieve efficient sealing in these films. Differential scanning calorimetry showed a decrease in the melting temperature from 104°C for LDPE to 101°C for both of the crosslinked LDPE films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1193–1199, 2005     

Dyeability and swelling properties of graft copolymers of LDPE with 2‐hydroxypropyl methacrylate monomer prepared by gamma radiation

Low density polyethylene (LDPE) films were grafted with 2‐hydroxypropyl methacrylate (HPMA) monomer by gamma radiation. The LDPE graft copolymer was characterized by FTIR spectroscopy, tensile mechanical testing, and thermogravimetric analysis (TGA). The dye affinity of LDPE graft copolymers for different dyestuffs was studied. Also, the effect of temperature on the swelling characters of LDPE‐g‐HPMA was investigated. The TGA study showed that the LDPE graft copolymers, over the studied graft yields, possessed higher thermal stability than pure LDPE polymer. While, LDPE has no dye affinity for any of the known dyestuffs, LDPE graft copolymers displayed a unique dye affinity for a wide range of dyestuffs belonging to different classes. The results showed that the equilibrium swelling of LDPE graft copolymers in water reached after 7 h. In addition, the results showed that the swelling of LDPE graft copolymers was influenced by temperature within the temperature range 10–40°C. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

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.     

Study of sulfonation mechanism of low‐density polyethylene films with fuming sulfuric acid

Sulfonation of low‐density polyethylene (LDPE) films with fuming sulfuric acid was studied by X‐ray photoelectron spectroscopy (XPS) and attenuated total reflectance (ATR) infrared spectroscopy. The ATR spectra showed the formation of C?C double bonds and multiple sulfur atom containing groups for the sulfonation of LDPE films. This led us to propose that the abstraction reaction of hydride ion by sulfur trioxide (SO₃) in fuming sulfuric acid might account for the formation of the C?C double bonds. It was considered that after the abstraction reaction, these double bonds react with SO₃, resulting in the production of alkene sulfonic acids and sultones, along with the formation of sulfate groups as a result of reaction of the double bonds with sulfuric acid. Experimental data by treatment of the sulfonated LDPE films with KOH and thiourea supported the proposed idea, estimating the approximate molar ratio of the products. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2435–2442, 2004     

Influence of reaction conditions on the formation of nanotubes/nanoparticles of polyaniline in the presence of 1‐amino‐2‐naphthol‐4‐sulfonic acid and applications as electrostatic charge dissipation material

BACKGROUND: Poly(1‐amino‐2‐naphthol‐4‐sulfonic acid) and its copolymers with aniline are a new class of conducting polymers which can acquire intrinsic protonic doping ability, leading to the formation of highly soluble self‐doped homopolymers and copolymers. Free ? OH and ? NH₂ groups in the polymer chain can combine with other functional groups that could be present in protective paints which can thus be successfully used as antistatic materials. RESULTS: This paper reports the formation of nanotubes of polyaniline on carrying out oxidative polymerization of aniline in the presence of 1‐amino‐2‐naphthol‐4‐sulfonic acid (ANSA) in p‐toluenesulfonic acid (PTSA) as an external dopant. The presence of ? SO₃H groups in the ANSA comonomer allows the copolymer to acquire intrinsic protonic doping ability. The polymerization mechanism was investigated by analysing the ¹H NMR, ¹³C NMR, Fourier transform infrared and X‐ray photoelectron spectra of the copolymers and homopolymers, which revealed the involvement of ? OH/? NH₂ in the reaction mechanism. Scanning and transmission electron microscopy showed how the reaction route and the presence of a dopant can affect the morphology and size of the polymers. Static decay time measurements were also carried out on conducting copolymer films prepared by blending of 1 wt% of copolymers of ANSA and aniline with low‐density polyethylene (LDPE) which showed a static decay time of 0.1 to 0.31 s on dissipating a charge from 5000 to 500 V. CONCLUSION: Copolymers of ANSA with aniline were synthesized in different reaction media, leading to the formation of nanotubes and nanoparticles of copolymer. Blends of 1 wt% of PTSA‐ and self‐doped copolymers of ANSA and aniline with LDPE can be formulated into films with effective antistatic properties. Copyright © 2009 Society of Chemical Industry     

Synthesis and photoluminescent properties of poly(aryl ether)s containing alternate emitting and electron‐transporting moieties

A new diphenylbutadiene‐containing bisphenol was successfully synthesized from benzylideneaniline and 4‐propenylanisole via an anil synthetic method. A series of copoly(arylene ether)s consisting of an alternate isolated blue chromophore (diphenylbutadiene) and an electron‐transporting moiety (1,3,4‐oxadiazole) was synthesized and characterized. High molecular weight copoly(arylene ether)s with an inherent viscosity of >0.5 dL/g were prepared by the nucleophilic displacement reaction of oxadiazole‐activated bis‐fluorocompounds with bisphenols. Introduction of ether linkages into the copolymers led to an enhanced solubility in organic solvents such as N,N‐dimethylacetamide (DMAc) and N‐methyl‐2‐pyrrolidinone (NMP). The resulting copolymers can be cast into tough and transparent films. The copolymers were amorphous in structure with high glass transition temperatures ranging from 182.29 to 194.50°C. They also exhibited good thermal stability with the maximum decomposition temperatures higher than 500°C in nitrogen. The absorption peaks of these copolymers in thin films varied from 375 to 391 nm, while the photoluminescent peaks varied from 410 to 433 nm. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1645–1651, 2003     

Development of new,nonabsorbable polymeric antioxidants for use in foods

The metabolic fate of a new, oil soluble antioxidant, selected from a series representing a unique class of phenolic polymers, is discussed together with its activity in unsaturated vegetable oils as compared to butylated hydroxytoluene, butylated hydroxyanisole, and tertiary butylhydroquinone (TBHQ). Using gel permeation chromatography,¹⁴C-radiolabeled polymer was isolated into discrete mol wt fractions and these administered as single oral doses to rats. Results indicate that while monomeric¹⁴C-TBHQ with a mol wt of 166 shows a total absorption of 88.3% of the administered dose, the absorption of polymeric antioxidant is vastly reduced with increasing mol wt; i.e., mol wt 760: 1.5%, mol wt 7300:0.44%, and mol wt 67,000: 0.34%. Functionality tests using the active oxygen method indicate that by increasing the phenolic constituents in the polymer composition the antioxidant activity can surpass that of certain traditional, monomeric food grade antioxidants. Stability tests using thermogravimetric analysis indicate the polymeric antioxidants are not depolymerized in the presence of air at temperatures up to 300 C. Further, the polymers are nonvolatile and under deep frying conditions result in nearly quantitative carry-through of antioxidant in that portion of oil absorbed by the food; a monomeric food grade antioxidant (TBHQ) shows losses due to volatilization. Presented at the AOCS Meeting, Dallas, April 1975.     

Study of ultraviolet photooxidative degradation of LDPE film containing cerium carboxylate photosensitizer

The carbonyl indices (CI) of photooxidation of low-density polyethylene (LDPE) films containing cerium carboxylate (CeCar₃) with/without aromatic ketones (AK) were determined by infrared (IR) spectroscopy. The effects of these photosensitizers on the rates of ultraviolet (UV) photooxidation of LDPE films and their mechanism in sensitizing photooxidative degradation are studied. Results show that CeCar₃ can cause the accelerated photooxidative degradation of LDPE films, but CeCar₃ in combination with AK may bring about the accelerated or retarded photooxidative degradation of LDPE films to varying degrees. After UV irradiation, followed by long duration storage, LDPE films containing these photosensitizers continued storage oxidative degradation at the storage oxidative rates similar to the past, except for the Michler ketone.     

Photolysis of poly(benzyl methacrylate)s and poly(benzyl acrylate)s in solution and films

Methacrylate and acrylate copolymers containing benzyl or 1‐phenylethyl groups and their monomeric model compounds were irradiated with a 254‐nm light in CH₂Cl₂ and solid films. Low molecular weight and polymeric products were analyzed by gas chromatography (GC) and NMR spectroscopy, respectively, and main‐chain scission efficiencies were determined by gel permeation chromatography (GPC). The results indicate that the ester bond cleavage in the side chain produces alkyl radicals in the main chain, leading to main‐chain scission and crosslinking. The higher stability of tertiary alkyl radicals formed in methacrylate polymers lead to the predominant main‐chain scission in solution. On the other hand, acrylate polymers were less susceptible to photodegradation. The degradabilities of the polymer films reflected those of the polymer solutions, although crosslinking preferentially occurred. The distinct effect of oxygen on the degradation was also observed in solution and films. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2227–2236, 2001     

Application of paraffin and silver coated titania nanoparticles in polyethylene nanocomposite food packaging films

In this work, 3% and 5% TiO₂/Ag nanoparticles were dispersed in low‐density polyethylene through melt blending process, and subsequently nanocomposite films were prepared by hot pressing. Paraffin was used for the first time in this work as compatibilizer agent. The effect of TiO₂/Ag nanoparticle content, as well as compatibilizer dosage on the antimicrobial, morphological, mechanical, and optical performance of the nanocomposite films was investigated. Improved mechanical properties of the nanocomposite films were found on using paraffin as compatibilizer in comparison with the neat low‐density polyethylene (LDPE) films. The optical study results also showed that the addition of TiO₂/Ag to the LDPE films does not drastically change the film appearance other than making them more reddish. The fabricated nanocomposites presented in this study could be a suitable choice for food packaging (subject to further investigation of the food packaging behavior). The results showed that both TiO₂/Ag nanoparticle and compatibilizer are needed to prevent the bacteria growth in the film. The best result was obtained by using 5% nanoparticle and 4% paraffin compatibilizer where the bacteria growth rate was significantly reduced by 95%. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45913.     

Surface modification of LDPE with PE‐PEO graft copolymer

Films of LDPE containing 1–10 wt % of various polymeric additives were prepared by different techniques. Three poly(ethylene‐graft‐ethylene oxide)s synthesized by grafting poly(ethylene‐co‐acrylic acid) with poly(ethylene oxide) monomethyl ether (MPEO), and two pure MPEOs having molecular weights 750 and 2000 were used as additives. The additives were mixed with LDPE both by blending in a common solvent and by melt mixing. The blends were then solvent cast from xylene onto glass Petri dishes or compression molded between glass plates. The film surfaces were studied by water contact angle measurements and by X‐ray photoelectron spectroscopy (XPS), and melting points and heats of melting were recorded by differential scanning calorimetry (DSC). The blends had a two‐phase morphology, with enrichment of the graft copolymers at the glass–polymer interface, as shown by contact angle values and XPS spectra. Large differences in the interface accumulation between the different film samples were observed. Films prepared by compression molding of solution‐mixed blends exhibited much lower surface accumulation of graft copolymer at the glass–polymer interface than did the solvent cast or melt‐mixed/compression‐molded samples. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 316–326, 2000     

Surface oxidation of low‐density polyethylene films to improve their susceptibility toward environmental degradation

Polyethylene wastes, particularly as films, have accumulated over the last several decades resulting in a major visual litter problem. The aim of this study was to investigate the ability of chemical reagents to oxidize the low‐density polyethylene (LDPE) film surface to increase their susceptibility toward photodegradation and thermal degradation. Three chemical agents, namely, potassium permanganate, potassium persulfate, and benzoyl peroxide, were used to oxidize the film surface to generate chromophoric groups, such as carbonyl groups, which are the main reason for the enhanced environmental degradation of photolytic polymers, such as ethylene–carbon monoxide and ethylene–vinyl ketone copolymers. For the chemical treatment, LDPE films of 70 ± 5 μm thickness were prepared by a film‐blowing technique and subsequently reacted with the aforementioned oxidizing agents. To aid the oxidation process, the reaction with potassium persulfate and potassium permanganate was performed under microwave irradiation heating. In the case of benzoyl peroxide aided oxidation, the films were subjected to repeated coating–heating treatments up to a maximum of 10 cycles. The treated films were subjected to accelerated aging, that is, xenon‐arc weathering and air‐oven aging (at 70°C), for extended time periods. The chemical and physical changes induced as a result of aging were followed by the monitoring of changes in the mechanical, structural, and thermal properties. The results indicate that the surface‐oxidized LDPE films exhibited enhanced susceptibility toward degradation; however, the extent was reduced as compared to photolytic or other degradable compositions. The ability of the chemicals to initiate degradation followed the order potassium persulfate < potassium permanganate < benzoyl peroxide. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Acrylic polyester resins containing perfluoropolyethers structures: Synthesis,characterization, and photopolymerization

Poly(ε‐caprolactone‐b‐perfluoropolyether‐b‐εcaprolactone) (PCL–PFPE–PCL) block copolymers having different PCL block lengths and end‐capped with methacrylate groups were prepared and characterized. Spectroscopic analyses confirmed the expected molecular structure of the products. After UV curing, the films revealed the presence of two amorphous phases, corresponding to fluorinated and hydrogenated moieties, respectively. The material containing long PCL blocks showed also a crystalline phase. Surface properties of the UV‐cured films were evaluated: The surfaces have a very high hydrophobic character in spite of the presence of many polar OH groups present in the polymeric network and a high hysteresis in wetting. An enrichment of fluorine at the air‐side surface was shown by contact‐angle measurements, except when long PCL sequences are present. The θ_adv angles decreased by increasing the content of PCL, that is, by decreasing the content of fluorine. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 651–659, 2000     

Influence of the Form II/Form I crystal polymorphism of random copolymers of butene‐1 with ethylene or propylene on the peel behavior of peel films

Peel films of blends of low density polyethylene (LDPE) and random isotactic copolymers of butene‐1 with either ethylene (iPB‐Eth) or propylene (iPB‐Prop) were investigated regarding the effect of the copolymer composition on both the Form II mesophase to Form I crystal transformation of the copolymers, and the time‐dependent peel behavior of their blends with LDPE in peel films. In general, there is observed a decrease of the peel force with increasing concentration of both ethylene and propylene co‐units in random iPB‐1 based copolymers and their blends with LDPE, after completion of the Form II to Form I transformation. Thus, to tailor the peel force, either the content of the peel component in the blends, or the concentration of ethylene or propylene co‐units in the peel component may be varied. The effect of ethylene co‐units in the random copolymers on the peel force is distinctly larger than that of propylene co‐units. Parallel to the Form II to Form I transition of butene‐1 based copolymers, the peel force decreases with a rate which depends on the copolymer composition. The Form II to Form I transition in iPB‐Prop copolymers proceeds distinctly faster than in iPB‐Eth copolymers of identical concentration of co‐units. POLYM. ENG. SCI., 55:1749–1757, 2015. © 2014 Society of Plastics Engineers     

Effect of crystallinity on surface morphology and light transmittance of poly(vinylidene fluoride‐co‐hexafluoropropylene) thin film

Homopolymer of vinylidene fluoride and its copolymers containing hexafluoropropylene (HFP) were prepared from free radical solution polymerizations and spin‐coated on the glass slides to fabricate thin film with a thickness of ～ 1 μm. It was found that the surface morphology of fluorinated thin films was strongly dependent on the crystallinity of polymers. In addition, the surface morphology was the most important factor to determine the optical transmittance of glass coated with the fluoropolymer thin film. As decreasing the crystallinity of the polymer by introducing HFP with a bulky CF₃ moiety, the surface of thin film became flattened and the transmittance of visible light was increased by reducing scattering. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Loss and transformation products of the aromatic antioxidants in MDPE film under long‐term exposure to biotic and abiotic conditions

The loss of a primary phenolic antioxidant Irganox 1010 and of a secondary phosphite antioxidant Irgafos 168 from a medium density polyethylene film (MDPE) was investigated after exposure of the film for 4 years to different environments such as aqueous media at pH5 and 7, open air, and compost, with an exposure of exposition of 25°C. An ultrasonic extraction technique using chloroform as extraction solvent was applied to recover the residual antioxidants from the polymeric matrix, and this was followed by High‐Performance Liquid Chromatography (HPLC) with acetonitrile as mobile phase and a quantitative analysis at a wavelength of 280 nm of the extracted antioxidants. The amount of antioxidant lost varied remarkably depending on the testing medium. The fastest loss of antioxidant was found on exposure to open air and sunlight while the slowest loss was observed in compost. Thermo‐analytical measurements were made to characterize the residual thermo‐oxidative stability of MDPE film in terms of oxidation temperature and oxidation induction time, to provide a greater insight into the underlying mechanisms of ageing in the different environments. Analysis by Gas chromatography–Mass Spectrometry (GC‐MS) revealed that degradation of the polymeric matrix resulted in the formation of hydrocarbons and oxygen‐containing compounds such as alcohols, carboxylic acids, aldehydes, and esters. The transformation products of the antioxidants formed as result of processing or exposure to the tested media were also identified. The transformation of the phenoxy radical of the Irganox 1010 produced the ester, acid, dealkylated cinnamate, and quinone products, whereas Irgafos 168 yielded oxidation products and the phenolic hydrolysis byproduct 2,4‐di‐tert‐butylphenol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 974–988, 2002