Investigation of high-density polyethylene film surface treated with chromic acid mixture by use of 2,4-dinitrophenylhydrazine. II. Film surfaces treated at 70°C

High-density polyethylene films were treated with chromic acid mixture at 70°C. The treated films were then reacted with 2,4-Dinitrophenylhydrazine. The changes in the amounts of carbonyl groups and 2,4-dinitrophenylhydrazones formed in the films were estimated by comparing their absorptions in the infrared and ultraviolet spectra, respectively. Scanning electron micrographs of the treated film surfaces were taken. Oxidation of the film surface zone, etching of the film surface zone, and oxidation of surface zone bared from the film inner zone seem to have occured with increase in treatment time. High-density polyethylene film surfaces were oxidized to a greater extent than low-density polyethylene film surfaces; however, the rate of etching of the low-density polyethylene film surface zone was larger than that of the high-density polyethylene film surface zone.     

Investigation of high-density polyethylene film surface treated with chromic acid mixture by use of 2,4-dinitrophenylhydrazine

High-density polyethylene films were treated with chromic acid mixture. 2,4-Dinitrophenylhydrazine was reacted on the treated films. The changes in amounts of 2,4-dinitrophenylhydrazones formed in the films were inferred by comparing the absorptions in the ultraviolet spectra. The changes in the film surfaces by chromic acid mixture treatment were investigated by comparing the changes in the amount of the hydrazones with changes in water wettability of the treated films. Scanning electron micrographs of the treated film surfaces were taken. Oxidation of the film surface zone, partial breakdown of polymer in the film surface zone, and oxidation of surface zone bared from the film inner zone seem to have occurred with increase in treatment time. When the treatment temperature was raised, the increase in carbonyl groups in the surface of the high-density polyethylene film with rise in treatment temperature seems to have been prevented by an increase in partial breakdown of polymer in the film surface.     

Formation of 2,4- dinitrophenylhydrazone on surface of polystyrene film irradiated with ultraviolet light. II. Regeneration of carbonyl groups and comparison with wettability

The 2,4-dinitrophenylhydrazones formed on irradiated polystyrene films were regenerated to carbonyl groups by immersing the films in levulinic acid solutions. The changes in the amount of carbonyl groups regenerated from the hydrazones were inferred by comparing the absorptions of the hydrazones at 378 mμ. The carbonyl groups were regenerated from the hydrazones with increase in regeneration times in the early stages of the regenerations and gradualy regenerated with increase in the regeneration times thereafter. The regeneration of the carbonyl groups was facilitated by raising the temperature in the levulinic acid solution, by adding dilute hydrochloric acid to the levulinic acid, or by raising the temperature in the levulinic acid solution containing hydrochloric acid. When the polystyrene films were irradiated for different periods of time, the increase in the critical surface tension of the films with increase in irradiation time showed a trend similar to the increase of amount of hydrazones formed on the surface zones with increase in irradiation time.     

Formation of 2,4-dinitrophenylhydrazone on surface zone of polystyrene film irradiated by ultraviolet light. I. Effects on formation of 2,4-dinitrophenylhydrazone

The hydrazones of the acetophenone-type 2,4-dinitrophenyihydrazone, formed by the reaction between 2,4-dinitrophenylhydrazine and carbonyl groups, was formed on the surface zone of irradiated polystyrene film. The changes in the amount of hydrazones formed on the films were inferred by comparing the absorptions in the ultraviolet and infrared spectra. The amounts of hydrazones formed increased with increase in irradiation time within about 3 hr and approached an asymptote with increase in irradiation time upward of about 4 hr. For the samples irradiated for 6 1/2 hr, the changes in the absorptions of the hydrazones stopped in about 3 min after the films were immersed in the 2,4-dinitrophenylhydrazine solution, the amounts of hydrazones formed increased with increase in the amount of benzene in the 2,4-dinitrophenylhydrazine solutions, the amounts of hydrazones formed slightly increased with rising temperature below 60°C in the solutions, and the rate of increase slightly increased with rise in temperature above 60°C in the solutions.     

Formation of 2,4-dinitrophenylhydrazones and regeneration of carbonyl groups in polyethylene film irradiated with ultraviolet light

2,4-Dinitrophenylhydrazine was reacted on polyethylene films irradiated in air with ultraviolet light. The changes in amount of carbonyl groups and 2,4-dinitrophenyl-hydrazones formed in the films were inferred by comparing their absorptions in the infrared and ultraviolet spectra, respectively. The amount of hydrazones formed increased with increase in the reaction time, and rates of the increase gradually decreased with increase in the reaction time. A comparison of the change in amount of hydrazones formed in the irradiated films with the change in amount of carbonyl groups formed in the irradiated films and the change in wettability with H-bonding liquids of the irradiated films showed that the amount of hydrazones formed seemed to be affected by amount of carbonyl groups in the surface zone of the film. The carbonyl groups were regenerated from the hydrazones with increase in the regeneration times, and rates of the regenerations gradually decreased with increase in the regeneration times. The regeneration was facilitated by raising the temperature in the levulinic acid solution, by adding dilute hydrochloric acid to the levulinic acid, or by raising the temperature in the levulinic acid solution containing hydrochloric acid.     

Diffusion of stabilizers in polymers. I. 2,4-dihydroxybenzophenone in polyolefins

The diffusion of the ultraviolet stabilizer 2,4-dihydroxybenzophenone in compressionmolded sheets of low-density polyethylene, high-density polyethylene, and isotactic polypropylene was investigated over the temperature range of 44–75°C. The magnitude of the diffusion coefficients for these polyolefins was found to decrease in the order low-density polyethylene > high-density polyethylene > polypropylene, the corresponding activation energies being approximately 18, 23, and 34 kcal/mole. Studies under conditions of saturation indicated that the migration of this stabilizer was confined to the more accessible amorphous regions of the polymers. The rate of loss of stabilizer from polymer samples immersed in water was also investigated at 44°C. Values of the diffusion coefficients calculated from the results of these studies were somewhat greater than those determined from the diffusion studies for the low-density polyethylene and isotactic polypropylene samples and considerably smaller in the case of high-density polyethylene. The extraction studies also permitted the quantitative evaluation of the solubilities of the stabilizer in the polymers. These were found to be 0.003, 0.03, and 0.07 wt-% for high-density polyethylene, low-density polyethylene, and polypropylene, respectively, at 44°C.     

Formation of 2,4-dinitrophenylhydrazones in polyethylene film treated with chromic acid mixture

2,4-Dinitrophenylhydrazones formed by the reaction of 2,4-dinitrophenylhydrazine with carbonyl groups were formed in polyethylene film oxidized with chromic acid mixture. The changes in amount of the hydrazones formed in the films were inferred by comparing the absorptions in the ultraviolet spectra and compared with changes in wettability with water of the films. In the early stage of treatment with chromic acid mixture, the hydrazone amount increased and the contact angle of water decreased. After the early stage of the treatment, the hydrazone amount decreased slightly and increased again thereafter, and the contact angle of water seemed to increased slightly and decreased again thereafter. The hydrazone amount increased with increase in time of the reaction between 2,4-dinitrophenylhydrazine and oxidized polyethylene film. For temperatures of treatment with chromic acid mixture above about 45°C, the hydrazone amount increased with rise in the treatment temperature and rate of the increase increased with rise in the treatment temperature, and the contact angle of water decreased with rise in the treatment temperature, and the rate of the decrease seemed to increased with rise in the treatment temperature.     

Urethane-based stabilizers for radiation-crosslinked polyethylene

Unsaturated urethane-based stabilizers for use in radiation-crosslinked polyethylene were synthesized. Aromatic amine moieties were attached to allylic and acrylic monomers by means of aromatic or aliphatic diisocyanates. The synthesized stabilizers were incorporated in high-density polyethylene films which were subjected to electron beam irradiation. The oxidative stability of the films prior to and after extraction was determined by DTA in the temperature range 185–210°C and compared with samples treated with commercial amine-bearing antioxidants. Tensile strength and gel content were also determined. Best results were obtained with a stabilizer prepared from equimolecular amounts of allyl alcohol, tolylene-2,4-diisocyanate and N-phenyl-1,4-phenylenediamine. Estimated lifetimes at 70°C of stabilized irradiated polyethylene samples were calculated.     

Identification of Unsaturated dinitrophenylhydrazones by partial hydrogenation

Small amounts of unsaturated carbonyl compounds, which originate from autoxidized fats, were converted into their corresponding 2,4-dinitrophenylhydrazones and subsequently partially hydrogenated. Neither hydrazine nor hydrogen gas and platinum oxide gave satisfactory results, but, using palladium on calcium carbonate as catalyst, the 2,4-dinitrophenylhydrazones could be hydrogenated partially. Only the double bonds of the aliphatic part of the molecule were reduced, whereas the carbon nitrogen double bond and the nitro groups were not attacked. After hydrogenation of 2,4-dinitrophenylhydrazones, the reaction mixture was analyzed by thin layer chromatography on a Kieselguhr plate impregnated with Carbowax. In this way, the chain length of the unsaturated carbonyl compound, as well as the number of double bonds, could be determined. Carbonyl conjugated double bonds appeared to be hydrogenated faster than isolated double bonds.     

Polyethylene Grafted Polyether Pentaerythritol Mono-Maleate to Improve Wettability of Liquid on Polyethylene Films

Blends of linear low density polyethylene (LLDPE) and linear low density polyethylene grafted polyether pentaerythritol mono-maleate (LLDPE-g-PPMM) were prepared by melt mixing. The surface of LLDPE/LLDPE-g-PPMM films with different contents of LLDPE-g-PPMM was characterized through contact angle and FT-IR spectroscopy. The tensile properties and light transmission properties of extruded films, as well as the performance of these films compared with commercial anti-fog films, were determined. The carbonyl polar groups on the surface of LLDPE/LLDPE-g-PPMM films increased, and the contact angles of water and glycerol decreased when the content of LLDPE-g-PPMM increased. LLDPE/LLDPE-g-PPMM films showed a noticeable reduction in water drop formation as the LLDPE-g-PPMM content was increased. The transmittancy and haze of LLDPE/LLDPE-g-PPMM films were improved when using increased contents of PPMM, which promotes better wetting of the water on the surface.     

Studies on Structure and Properties of HDPE Functionalized Through Ultraviolet Irradiation and Its Blends with CaCO3

Abstract

The structure and properties of high-density polyethylene (HDPE) functionalized through ultraviolet irradiation in air and its blends with CaCO₃ were studied by Fourier transfer infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), contact angle measurement, Molau test, and mechanical properties test. The experimental results reveals that oxygen-containing groups such as C = O and C - O were introduced onto the molecular chains of HDPE through ultraviolet irradiation in air, and the groups' concentration increases with irradiation time. After irradiation, the water contact angle of HDPE becomes smaller, showing that the hydrophilicity of irradiated HDPE increases. Compared with those of HDPE/CaCO₃ blend, the dispersion of CaCO₃ particles in irradiated HDPE/CaCO₃ blend, the interface interaction between CaCO₃ particles and irradiated HDPE matrix, and the mechanical properties of irradiated HDPE/CaCO₃ blend are improved due to the introduction of polar groups.     

Characterization of LLDPE/LLDPE-g-AA Blends by Contact Angle and FT-IR Methods

Abstract

Blends of linear low density polyethylene (LLDPE) and linear low density polyethylene-grafted-acrylic acid (LLDPE-g-AA) were prepared by melt mixing. The surface of films with different content LLDPE-g-AA were characterized through contact angle measurements and FT-IR spectroscopy. The contact angles of water and glycerol on films surfaces of LLDPE/LLDPE-g-AA blends decrease with increase of LLDPE-g-AA. From FT-IR spectra of the blends, the carbonyl peak strength on the films surface was calculated. It was found that larger the carbonyl peak strength, the lower the value contact angle for LLDPE/LLDPE-g-AA blends.     

Electron-beam irradiation-induced grafting of acrylonitrile onto polyethylene

Low- and high-density polyethylene (PE) films were grafted with acrylonitrile (AN) by electron beam prior to irradiation. The distribution of graft chains over the cross section of the sample film was analyzed in terms of the distribution of nitrogen atoms contained in the AN by means of an electron probe microanalyzer (EPMA), and graft sites were studied in relation to the effect of grafting temperature on the percent graft and the oxygen permeability of the sample films. It was found that diffusion of AN into the film was the rate-limiting step in the grafting process, thus restricting the grafting to the surface of the film in the initial grafting stages. However, the grafting shifted to the center of film as the graft process proceeded, until a uniform distribution of graft chains was observed across the entire film thickness. High-density polyethylene (HDPE) was found to display a higher percent graft than did low-density polyethylene (LDPE), and percent graft tended to increase with increasing grafting temperature. On the other hand, film oxygen permeability decreased with increasing percent graft, but this decreasing trend decreased with increasing percent graft. These findings suggest that the grafting is initiated by radicals trapped in the amorphous phase near the crystalline regions and at the surface of crystallites and that graft chains grow toward the amorphous regions. As for the radicals contributing to graft polymerization, it appears that AN permeates deeper near the crystalline surface and that graft chains grow from these sites.     

Structure–property behavior of polyethylene exposed to different types of radiation

A detailed study was performed on unirradiated low‐ and high‐density polyethylene (LDPE and HDPE) films as well as irradiated films with different types of radiation such as ⁶⁰Co γ rays, thermal and fast neutrons, and electron beam irradiation. The structural changes of PE films were characterized by Fourier transform infrared (FTIR), Fourier transform Raman (FT–Raman), and ultraviolet (UV) spectrometric techniques. The results showed significant radiation degradation, crosslinking, and changes in the crystalline and amorphous regions. The influence of γ‐radiation on the structure of PE was found to be more prominent compared to that of thermal neutrons and electron beam irradiation. However, LDPE film was found to be more sensitive to these types of radiation in accordance with HDPE because of its lesser degree of crystallinity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 179–200, 2000     

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.     

Effect of storage on ultraviolet irradiated HDPE

Abstract

Oxygen containing groups such as C=O and C–O were introduced onto high density polyethylene (HDPE) chains by ultraviolet (irradiated at 70°C and different light intensities in air). The contents of oxygen containing groups were unchanged after storage, indicating that these groups were stable in HDPE chains. The water contact angles of the irradiated HDPE at different light intensities after storage were equivalent to those of the irradiated HDPE before storage. Small quantity of the irradiated HDPE at different light intensities before and after storage as a compatibiliser were added into the HDPE/CaCO₃ composite respectively, and the HDPE/CaCO₃/irradiated HDPE before and after storage composite were prepared respectively. The tensile strength and the impact strength of HDPE/CaCO₃/irradiated HDPE after storage composite were similar to those of the HDPE/CaCO₃/irradiated HDPE before storage composite. The irradiated HDPE after storage was an efficacious compatibiliser.     

The preparation and tensile properties of polyethylene composites

Single polymer composites have been prepared using different morphologies of polyethylene as matrix and as the reinforcement. Depending on annealing conditions, the ultraoriented fibers used as reinforcement can have higher melting points (ca. 139°C) than the matrix made from the same conventionally crystallized high-density polyethylene (ca. 132°C) or from low-density polyethylene (ca. 110°C). The optimum temperature has been assessed for bonding to occur by growth of transcrystalline regions from the melt matrix without considerable modulus reduction of the annealed ultraoriented and reinforcement fiber or film. Pullout tests have been used for determining the interfacial shear strength of these single polymer composites. The interfacial shear strength for the high-density polyethylene films embedded in a low-density polyethylene matrix is 7.5 MPa and for high-density polyethylene self-composites is 17 MPa. These values are greater than the strength for glass-reinforced resins. The strength is mainly due to the unique epitaxial bonding which gives greater adhesion than the compressive and radial stresses arising from the differential shrinkage of matrix and reinforcement. The tensile modulus of composites prepared from uniaxial and continuous high-density polyethylene films embedded in low-density polyethylene obeys the simple law of mixtures and the reinforced low-density polyethylene modulus is increased by a factor of 10. High strength cross-ply high-density-polyethylene—low-density-polyethylene laminates have also been prepared and the mechanical properties have been studied as the film orientation is varied with respect to the tensile axis.     

Enhancing the permeation characteristics of polyethylene by membrane irradiation in the fully swollen state

Fully swollen, low-density polyethylene films were irradiated, vacuum dried, reswollen, and subsequently permeability tested using tritiated toluene and benzene as penetrants. The treatment improved the permeability of polyethylene up to 88%, with the enhancement strongly dependent on the choice of the irradiation solvent. These results suggest a potentially practical process for improving the performance of semipermeable membranes.     

Surface modification of polyethylene by photochemical grafting with 2-hydroxyethylmethacrylate

The photochemical grafting of 2-hydroxyethylmethacrylate onto low-density polyethylene film is described. The grafting technique employed involved irradiating a solution of 2-hydroxyethylmethacrylate and benzophenone in acetone spread between films of poly(ethylene terephthalate) or glass and low-density polyethylene. After irradiation for 2 min, the contact angle of the polyethylene films with water fell from 97° to about 50°. The contact angle of the poly(ethylene terephthalate) substrate also fell during grafting. X-ray photoelectron spectroscopy was consistent with the presence of poly(2-hydroxethylmethacrylate) at the surface of the polyethylene. The effect of solvent on the photochemical grafting of 2-hydroxyethylmethacrylate onto low-density polyethylene is discussed. © 1993 John Wiley & Sons, Inc.     

A study of LLDPE functionalized through ultraviolet irradiation and interfacial interaction of PA66/functionalized LLDPE blends

Some oxygen‐containing groups, such as C? O? C, C? OH, C?O, C(?O)O, and C(?O)OH, were introduced onto linear low‐density polyethylene (LLDPE) chains during ultraviolet irradiation under air, without adding any monomers and auxiliaries and without environmental pollution. After ultraviolet irradiation, the molecular weight of LLDPE decreased and its distribution became wider. The melting temperature and crystallinity of irradiated LLDPE decreased with irradiation time. The copolymer LLDPE‐g‐PA66 was formed by reaction between oxygen‐containing groups of irradiated LLDPE and amine or carboxyl end groups and amide linkage of polyamide 66 (PA66) during preparation of PA66/irradiated LLDPE blends. Compared with PA66/LLDPE blend, the mechanical properties of PA66/irradiated LLDPE blends were improved greatly because of the improved interface interaction and dispersion. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006