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.     

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.     

Change of polypropylene film surface by chromic acid mixture treatment

Polypropylene films were treated with chromic acid mixture. The change in the treated films was investigated by comparing change in amount of 2,4-dinitrophenylhydrazones formed in the treated films with their change in wettability with water. 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 seemed to occur with increase in treatment time or with increase in treatment temperature.     

Formation of 2,4-dinitrophenylhydrazones in high-density polyethylene film irradiated with ultraviolet light

Polyethylene films were irradiated in air by ultraviolet light. 2,4-Dinitrophenylhydrazine was reacted on the irradiated films. The changes in amounts of carbonyl groups and 2,4-dinitrophenynlhydrazones formed in the films were inferred by comparing their absorptions in the infrared and ultraviolet spectra, respectively. It seems that the contents of carbonyl groups formed in the amorphous regions in the high-density polyethylene films by the irradiation were larger than the contents of carbonyl groups formed in the amorphous regions in the low-density polyethylene films. The decreases in contact angles of water on the high-density polyethylene films by the irradiation were larger than the decreases in the contact angles on the low-density polyethylene films. The amounts of 2,4-dinitrophenylhydrazones formed in the irradiated high-density polyethylene films were less than the amounts of 2,4-dinitrophenylhydrazones formed in the irradiated low-density polyethylene films.     

Molecular orientation in film extrusion of high-density polyethylene

Molecular orientation in film extrusion has been studied using an extrusion-grade commercial polyethylene resin. First quad (take-up) speed was varied over the range 50 to 120 m/min, Web crystallinities were found to be in the range 0.60 to 0.65 as determined by differential scanning calorimetry. Web crystalline orientation function f_c was slightly negative below a takeup speed of 50 m/min and rose to a value of 0.4 at 120 m/min at a quench bath temperature of 37.8°C and a melt temperature of 251°C for one of the resins used. (Perfect orientation along the machine direction implies f_c equal to 1.0). Amorphous orientation function f_a remained below 0.1 and was almost constant with takeup speed. This behavior was modified in a minor way by changes in quench bath and melt temperature as well as resin lot. A qualitative model was proposed for this without definite proof. The major mechanism at work in the film-forming process is macromolecular network structure deformation in elongational flow. Die gap variation at uniform extrusion rate has a secondary effect on web orientation. With the present state of knowledge, it is not possible to quantitatively separate the amorphous orientation function into its various conformational contributions. It was also noted that high take up speeds and low air gaps tend to freeze the web at greater widths.     

Determination of carbonyl groups in polymers by reaction with 2,4-dinitrophenylhydrazine

The 2,4-dinitrophenylhydrazine (DNPH) analysis of oxygenated functional groups in model polymers has been investigated. Whereas, aldehydic functional groups can be quantitatively analysed by previously reported methods, ketonic groups are only partially detected. Carboxylic, ester and epoxy groups do not significantly interfere in the conventional analytical methods. The reactivity of polymeric carbonyl groups towards DNPH appears to be markedly affected by steric factors, determined by the polymeric microstructure. The applicability of the DNPH method to the analysis of oxygenated functional groups in natural rubber and oxidized poly(ethylene) is discussed.     

Etching of a low-density polyethylene film by fuming nitric acid

Low-density polyethylene (LDPE) films were treated with fuming nitric acid (FNA). The surface characteristics and also the insertion of polar groups like on the etched LDPE film surface were measured by SEM, IR and XPS analyses, respectively. The mechanical performance of a laminate of the etched film with epoxy resin and also the printability of the etched film surface were tested and compared with the unetched sample. The surface roughening and the presence of polar groups enhance the mechanical strength of the laminate of FNA-treated film due to mechanical interlocking and chemical interaction. The printability of the treated film surface is also superior to that of the untreated LDPE film surface.     

Reaction of 2,4-dinitrophenylhydrazine with methylvinylketone copolymers. Effect of steric environment

The reaction of 2,4-dinitrophenylhydrazine (DNPH) with methylvinylketone copolymers of styrene, methylacrylate, methylmethacrylate and cyclohexylmethacrylate has been studied. The equilibrium nature of the reaction is clearly observable leading to non-quantitative reactions under all conditions investigated. The equilibrium constant (K) for hydrazone formation decreases in the order methylacrylate>styrene?methylmethacrylate>cyclohexyl methacrylate indicative of pronounced steric effects. The temperature dependence of K reveals that the reaction is thermodynamically, rather than kinetically, controlled.     

Melt spinning flow behaviour of high-density polyethylene blended with low-density polyethylene

ABSTRACT

The melt spinning flow behaviour of a high-density polyethylene (HDPE) blended with a low-density polyethylene (LDPE) was studied using a melt spinning technique in temperature ranging from 160 to 200°C and die extrusion velocity varying from 9 to 36?mm?s^?1. The results showed that the melt apparent extension viscosity of the blends was higher than those of the LDPE and HDPE; the melt apparent extension viscosity decreased with increasing temperature; while the melt apparent extension viscosity increased with increasing extension strain rate when the extension strain rate was lower than 0.2?s^?1, and then decreased; the melt apparent extension viscosity reached up to a maximum value when extension strain rate was about 0.2?s^?1; the relationship between the melt apparent extension viscosity and the LDPE weight fraction did not follow the mixing rule.     

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.     

Loss of 2-tertiary-butyl-4-methoxy phenol (BHA) from high-density polyethylene film

The rate of loss of the antioxidant 2-tertiary-butyl-4-methoxy phenol (BHA) from high-density polyethylene (HDPE) was determined using high pressure liquid chromatography (HPLC). The rate of loss was found to follow a first-order expression. Almost all of the antioxidant was lost (>95 percent) within 1 day at 50°C, within 3 days at 40°C, and within 7 days at 30°C. The controlling parameter for mass transfer of the antioxidant was found to be volatilization rather than diffusion.     

低温等离子体处理对高强聚乙烯纤维表面影响的研究

采用空气低温等离子体处理高强聚乙烯纤维,测试处理前后纤维表面摩擦系数的变化,并采用电子扫描显微镜（SEM）和原子力显微镜（AFM）对纤维表面形貌进行观察分析。结果发现,空气低温等离子体处理的刻蚀作用会在纤维表面形成致密的＂小坑群＂,使得纤维表面产生剥落、联结,造成纤维表面的粗糙程度有所增加,其处理后的纤维表面静、动摩擦系数有所提高。     

表面接枝高密度磺酸基聚苯乙烯的制备及表征

以无水溴化铝为催化剂,对氯苯甲醛为醛基化试剂,通过傅克反应在聚苯乙烯微球表面接枝醛基;基于醛基的可氧化性,利用还原剂硝酸铵铈将树脂微球表面的醛基自由基化,引发对苯乙烯磺酸钠在树脂微球表面聚合,并对其进行表征。结果表明,聚苯乙烯微球磺酸化改性成功,优化的磺化工艺条件为:醛基含量1.5 mmol/g的聚苯乙烯微球用量0.3 g,对苯乙烯磺酸钠质量浓度40 g/L,硝酸铵铈质量浓度40 g/L,反应温度70℃,在此条件下制备的树脂表面磺酸基含量为58 mmol/g。     

Estimation of surface properties of grafted layers formed on low- and high-density polyethylene plates by photografting of methacrylic acid and acrylic acid at different monomer concentrations and temperatures

An investigation was carried out on estimation of hydrophilicity, wettability and water-absorptivity, and surface analysis by X-ray photoelectron spectroscopy of the low- and high-density polyethylene (LDPE and HDPE) plates photografted with methacrylic acid (MAA) and acrylic acid (AA) at different monomer concentrations or temperatures. Wettability of the MAA-grafted LDPE and HDPE plates increased with grafted amounts, and became constant when the substrate surfaces were fully covered with the grafted polymer chains. On the other hand, for the AA-grafted LDPE and HDPE plates, wettability had the maximum value, and then gradually decreased against the grafted amount probably due to aggregation of grafted PAA chains, although the surfaces were covered with grafted PAA chains at lower grafted amounts compared with grafted PMAA chains. Water-absorptivity sharply increased at lower grafted amounts due to formation of shorter grafted polymer chains for photografting at lower monomer concentrations or due to restriction of the location of grafting to the outer surface region for photografting at lower temperatures. Therefore, for photograftings of AA or onto the HDPE plates, the substrate surfaces were covered with grafted polymer chains and the grafted layers formed possessed higher water-absorptivity at lower grafted amounts. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Cylindritic structures of high-density polyethylene molded by multi-melt multi-injection molding

The crystalline morphologies of high-density polyethylene (HDPE) molded by multi-melt multi-injection molding (MMMIM) and conventional injection molding (CIM) were studied by employing polarizing light microscopy (PLM) and scanning electronic microscopy (SEM). It was found that a special double skin-core structure was formed in MMMIM parts. Namely cylindritic structures appeared in both sub-skin layer and core layer, which were attributed to the strong shear flow introduced by the secondary melt penetration process. As the decrease in temperature and injection pressure of the second melt, the number of cylindritic structures in the core layer decreases and the cylindritic structures gradually develop into irregularly-arranged spherulites. Strong shear flow, as compared to CIM, is an important factor which dictates the formation of cylindritic structures in MMMIM. Meanwhile, on going from the interface to the core of MMMIM parts the distance between the centers of banded spherulites which consist of cylindritic structures and the radius of them increased gradually. This phenomenon was primarily caused by the coupling effect of the decreased shear intensity and the cooling rate of melts towards core layer. Based on the above observations, a modified model is proposed to interpret the mechanism of the formation of cylindritic structures during MMMIM process.     

Thermosensitive surface properties of polyethylene film with poly(N-isopropylacrylamide) chains prepared by corona discharge induced grafting

Polyethylene (PE) film was treated by corona discharge and then grafted with N-isopropylacrylamide (NIPAAm) for modification of the surface. The grafted amount was determined by gravimetry and the surface morphology was observed by using a scanning electron microscope. The surface analysis was carried out with a x-ray photoelectron spectroscopy and electron probe microanalysis. It was clarified that grafting was limited surface and there was no change of the surface morphology after grafting. The water absorption at various temperature under the absolute humidity (11.4 g/cm³) and the leakage of electrostatic charge from PE film were measured. PolyNIPAAm that was introduced onto PE surface has hydrophilic-hydrophobic transition properties at the 32°C in the atmospheric condition. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1773–1779, 1998     

Properties of bamboo flour/high-density polyethylene composites reinforced with ultrahigh molecular weight polyethylene

In order to improve the properties of bamboo-plastic composites (BPCs), bamboo flour/high-density polyethylene (HDPE) composites were reinforced with ultrahigh molecular weight polyethylene (UHMWPE). The effects of UHMWPE on properties of composites were studied. The crystallinity of composites decreased slightly. Compared with non-UHMWPE added bamboo powder/HDPE composite, the composite with 6 wt % UHMWPE, showed decrease in water absorption to 0.41%, whereas its tensile strength and flexural strength increased to 34.51 and 25.88 MPa, respectively, a corresponding increase of 34.59 and 12.87%. The temperatures corresponding to initial degradation temperature (T_initial) and maximum degradation temperature (T_max) of the composite increased from 282.7 and 467.4 °C to 288.5 and 474.7 °C respectively. Scanning electron microscopic images showed that UHMWPE was well dispersed and fully extended as long fibers in the composite, forming a “three-dimensional physically cross-linked network structure,” which contributed to the improved properties of the composites. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48971.     

Investigation of crystallinity effects on the surface of oxygen plasma treated low density polyethylene using X-ray photoelectron spectroscopy

Plasma treated polymer surface shows rapid hydrophobic recovery after plasma treatment. Surface rearrangement and the hydrophilicity change of low density polyethylene (LDPE) films with different degrees of crystallinity after oxygen plasma treatment were investigated using X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Since the mobility of polymer chain was restricted in the crystalline region, the chain movement of high crystalline polymer would be reduced. Water contact angles of quenched and annealed LDPE just after plasma treatment were almost same and oxygen contents of quenched LDPE was slightly higher than that of annealed LDPE. However, annealed LDPE showed slower contact angle raise and kept higher oxygen concentration than quenched LDPE with increasing aging time. By deconvolution of carbon XPS spectra, it was observed that major group contributed to decrease of oxygen contents was the hydroxyl groups and hydroxyl groups of quenched LDPE decayed faster than annealed LDPE while other oxygen species kept constant or decreased slightly. Increasing crystallinity reduce the surface rearrangement of polymer chain after plasma treatment.     

Copolymer of acrylonitrile/acrylic acid solid surface film dendrigrafted with citric acid

BACKGROUND: The aim of the present work was to improve the properties of acrylic polymer, which is a major fibre‐forming polymer. Acrylonitrile/acrylic acid copolymer, P(AN/AA), was chosen for this purpose and it was intended to study the condition for the formation of hydroxyl groups through the formation of hyperbranched polymers. RESULTS: The synthesis of a dendritic polymer of citric acid (CA) in the solid phase on a P(AN/AA) core is described. The product was analysed using the elemental analysis technique and ¹H NMR. Dendritic molecules were grown by a reaction between the carboxylic acid of acrylic acid and hydroxyl group of CA activated by dicyclohexylcarbodiimide. Products were analysed using Fourier transform infrared and NMR spectroscopy. CONCLUSION: The formation of CA dendrigraft on P(AN/AA) films in a heterogeneous system is possible. The percentage conversion of the copolymer reaction with CA was calculated based on the NMR results. The percentage conversion showed a gradual reduction with an increase in step numbers. The contact angle of water on the films was affected by the percentage conversion of the reactions. A calculation scheme is presented to show that the low degree of conversion leads to an increase in hydrophobic groups. Copyright © 2008 Society of Chemical Industry     

Thermo-oxidative aging of high-density polyethylene reinforced with multiwalled carbon nanotubes

The purpose of this study was to investigate the influence of aging on the properties of high-density polyethylene (HDPE) reinforced with multi-wall carbon nanotubes (MWCNTs). Nanocomposites were prepared with nanotubes at 0, 1, 3, and 5 wt%. The long-term durability of the prepared materials was evaluated by thermo-oxidative aging test. Test bodies were aged at 110°C for up to 10 weeks. The nanocomposites were characterized by differential scanning calometry, thermogravimetric analysis (TGA), ¹³C-NMR, elongation at break, and transmission electron microscopy. The aging mainly occurred on the surface of the samples and the neat HDPE showed a strong yellowing after the aging. A strong reduction in elongation at break was seen. For neat HDPE, the elongation at break was reduced from roughly 1400–25%. When HDPE was reinforced with the nanotubes, the reduction was less dramatic.