Bulk surface photografting process and its application. III. Photolamination of polymer films

This paper introduces a set of new concepts related to the macromolecular design and to the practice in the realm of lamination by photografting, with experimental studies of the synthesis, structure, and performance of various systems, including valence bond adhesion of the organic polymeric materials, hyperbranched macromolecules rooted to the surface of organic substrates, macromolecular networks rooted on and bridged between two organic substrates, and a synthetic route combining primary and secondary photografting processes for the preparation of supermolecular architectures. In successful photolamination experiments based on these ideas, hyperbranched macromolecules of large size (10–20 μm) were obtained after initiation with aromatic ketones, which undergo a photoreduction reaction. A range of different organic polymeric films have been laminated. T-peel tests show most of the laminates broke inside the substrates and not at the interface between adhesive and substrate. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1723–1732, 1997     

聚合物光接枝表面改性的方法和影响因素

简要介绍了聚合物光接枝表面改性的方法，并分析了聚合物光接枝表面改性的几种方法，着重分析了基体、接枝单体、光敏剂、溶剂、接枝方法、温度和光照时间等因素对聚合物光接枝表面改性的影响。     

Surface functionalization of poly(lactic acid) film by UV‐photografting of N‐vinylpyrrolidone

The photoinitiated grafting of N‐vinylpyrrolidone (NVP) onto poly(lactic acid) (PLA) film with the use of benzophenone (BP) as the initiator, modified the natural hydrophobic PLA behavior to an hydrophilic film with desirable wettability. The surface photografting parameters‐percent conversion of monomer to overall photopolymerization (Cp), percent conversion of monomer to the photograft polymerization (Cg), and grafting efficiency (Eg) were calculated. The resulting film surface was analyzed using ATR‐FTIR and UV spectroscopy, derivative spectroscopy and water contact angle. Besides, we demonstrated that the grafted polyvinylpyrrolidone chains could easily react with iodine to form a complex as the homopolymer does with antibacterial activity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface modification of low density polyethylene films by homogeneous catalytic ozonation

Low density polyethylene films were treated by ozone to generate peroxides on the surfaces. The peroxides generated are capable of initiating radical graft polymerization of hydrophilic vinyl monomers onto the polymers, resulting in hydrophilic surfaces. Results of ozonation revealed that molecular ozone instead of hydroxyl radicals was the main oxidant for peroxide generation. A novel approach, aqueous ozonation with the addition of a soluble transitional metal salt, FeCl₃, as a homogeneous catalyst, was proposed and proved to be successful in this study. The addition of FeCl₃ could increase peroxide generation by 22.7%, compared to its non-catalyzed counterpart. An optimum catalyst concentration, 0.04 g/L, was determined. Also, the effects of pH, ozonation time and applied ozone dose on peroxide generation were investigated. The loss in tensile strength of the films would be 15% or less if the applied ozone dose was not over 2 wt.%. The functional groups generated on the film surfaces were characterized by FTIR, the contact angle and surface roughness of the film were also examined before and after ozonation.     

Kinetic study of hindered amine light stabilizer photografting in low density polyethylene films under natural weathering conditions

The photografting kinetic of a hindered amine light stabilizer (HALS) was studied in low density polyethylene (LDPE) films under natural weathering conditions. The HALS (PBH‐3) was added to the polymer at a concentration of 0.3% (w/w). The photografting kinetic of polymer bound HALS (PBH‐3) was determined by direct spectroscopic measurements through the absorption band area of the stabilizer centered at 308 nm in the UV spectra and 1605 cm^?1 in Fourier transform IR (FTIR) spectra, which correspond to benzylidene malonate ester and benzylidene malonic groups, respectively. In parallel, measurements were carried out on the free PBH‐3 content after chloroform extraction of the photostabilizer from the polymer matrix by means of UV and gas chromatography methods. The results showed that in natural weathering the grafting of PBH‐3 occurred in the LDPE film after very short exposure times of 127 and 168 h as determined by UV and FTIR, respectively. Moreover, the curves describing both the photografting and the free HALS kinetics exhibited similar profiles. The mechanism of photografting implies a rapid photoreaction between the methylenic double bond of the stabilizer and the macroalkyl radicals of the polymer, resulting in formation of polymer‐bonded aminyl derivatives of the stabilizer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1524–1532, 2002; DOI 10.1002/app.10492     

Ultraviolet-initiated photografting of glycidyl methacrylate onto styrene–butadiene rubber

Photografting reaction onto styrene–butadiene rubber (SBR) as a function of monomer concentration, grafting method, irradiation time, and the carbon black content has been studied using ultraviolet (UV). Glycidyl methacrylate and benzophenone are used as monomer and initiator, respectively. The occurrence of graft reaction onto SBR surface is identified by infrared attenuated total reflection (IR-ATR) analysis. The degree of monomer graft increases with monomer concentration and tends to level off at high monomer concentration (>8.3M/L). Graft ratio also increases with UV irradiation time. Carbon black content is found as one of important factors that determine the monomer graft efficiency. The amount of monomer graft onto SBR decreases with increasing carbon black content and it is attributed to the reduction of irradiation absorbance due to the presence of carbon black. The occurrence of reaction between glycidyl methacrylate grafted SBR and nylon-6 via melt phase reaction is also identified using IR-ATR analysis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1733–1739, 1999     

Surface modification of polyester films by RF plasma

Plasma treatment of PET films was carried out under argon, followed by exposure to an oxygen atmosphere. The films underwent considerable changes in surface composition and morphology, as demonstrated by contact angle measurements, FTIR‐ATR, AFM, and XPS. It was found that the surface acquired oxygen containing polar functional groups such as —C=O, —OH, and —OOH, which increased in number as the plasma treatment time increased. During storage, the treated films underwent significant surface reorganization, and both the time and temperature contributed to the increase in the contact angle. As revealed by AFM measurements, these changes were accompanied by an increase in roughness in the form of ridges. The ridges were observed to grow in height with increasing treatment time, although their spacing showed little evolution. A correlation among the observations obtained from various techniques was established, giving a comprehensive picture of the structure and dynamics of plasma‐treated PET surfaces. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1083–1091, 2000     

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     

Modification of adhesive properties of a polyethylene film by photografting

Graft polymerization of acrylic acid from monomer solutions in water or in bulk onto low‐density polyethylene film substrate was carried out by the method of continuous process under UV radiation. Effects of the nature of photoinitiator on acrylic acid grafting was first studied. One PI₂ and two PI₁ photoinitiators were used. Benzophenone was then retained for the following study. The influence of photoinitiator and monomer concentration was investigated by determining polymerization kinetics and grafted polymer amount. A study of surface wetting and morphological structure was then carried out on a bulk system and as a function of the photoinitiator concentration. Finally, such surface modification was studied with respect to its effect on the adhesion of an acrylic stick on its surface. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2803–2811, 2004     

Photoinitiated grafting of methyl methacrylate on highly oriented polyethylene: Effect of draw ratio on grafting

Modification of highly oriented polyethylene was performed using a photoinitiated grafting technique. The samples were first coated with photoinitiator and then exposed to methyl methacrylate vapor under UV light (λ > 290 nm) at 60°C. The extent of grafting was studied as a function of draw ratio. It was found that the extent of grafting decreased significantly as the draw ratio was increased. Control samples of undrawn samples with different thermal histories suggested that there was another factor in addition to crystallinity that influences the extent of grafting. It is proposed that amorphous orientation or taut-tie molecules reduce the photoinitiation process. Gravimetric and attenuated total reflectance-IR measurements indicated that the grafting reaction can occur below the sample surface (or internal grafting) and that the proportion of surface grafting increases with increasing draw ratio. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 465–470, 1998     

Characteristics of methacrylic acid‐grafted polyethylene films prepared by photografting in the presence of polyfunctional monomers

Photografting of methacrylic acid (MAA) on low‐density polyethylene film (thickness = 30 μm), on which xanthone photoinitiator was coated earlier, in the presence of polyfunctional monomers such as N,N′‐methylenebisacrylamide, ethylene glycol dimethacrylate, and trimethylol propane triacrylate was examined at 60°C in water/acetone (3:1 v/v) mixture solvent. The photografting was retarded at the earlier stage of polymerization, and then accelerated when small amounts of the polyfunctional monomers (1–3 mol % of MAA monomer used) were added to the system. Addition of the polyfunctional monomers did not affect distribution of the grafted chains in the cross section of the resultant MAA‐grafted PE film, which was measured by electron probe microanalysis. The MAA‐grafted samples were subjected to adsorption of cupric ions at 25°C for 24 h in the system of pH = 5. The adsorption was considerably suppressed for the grafted samples prepared at the earlier stage of polymerization in the system with the polyfunctional monomers. The phenomenon was discussed in terms of the formation of crosslinked and branched structures in the MAA‐grafted chains depending on the polymerization stage in the system with polyfunctional monomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1262–1268, 2006     

Surface changes of corona‐discharge‐treated polyethylene films

Morphological and chemical changes of the surface of low‐density polyethylene (LDPE), linear middle‐density polyethylene (L‐MDPE), and their 80/20 blend were studied by different techniques after corona‐discharge treatment in air and subsequent annealing. The surface tension was determined by wetting; the roughness was measured by atomic force microscope (AFM), and the surface chemical composition was analyzed by X‐ray photoelectron spectroscopy (XPS), whereas the low‐molecular‐mass fraction washed off by chloroform by FTIR. The surface tension of the films increases with the electrode current. The surface roughness depends primarily on the polymer type and is less affected by the corona treatment. At the initial stage of annealing, posttreatment‐type oxidation and hydrophobic recovery are competing. The former is more pronounced in L‐MDPE, the latter in LDPE. After annealing at 50°C for 160 days, hydrophobic recovery becomes predominant in each film studied, which is accompanied by significant smoothening of the surface. According to XPS and FTIR results, this is due to the migration of low‐molecular‐mass components (oligomers, oxidized polymer fractions, and additives) to the surface. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1529–1541, 2000     

Characteristics of acrylic acid and N-isopropylacrylamide binary monomers–grafted polyethylene film synthesized by photografting

Method for introducing grafted chains consisting of two types of monomer components, acrylic acid (AA) and N-isopropylacrylamide (NIPAAm), into low-density polyethylene (PE) film (thickness = 25 μm) was investigated by two photografting technique using xanthone photoinitiator at 60°C. In the first method (one-step method), AA and NIPAAm binary monomers were graftcopolymerized onto PE film. In the second method (two-step method), AA was first photografted onto PE film and then NIPAAm was further introduced into the AA-grafted PE film by a second-step photografting. Water absorbencies of the grafted films (one- and two-step samples) prepared by the one- and two-step methods, respectively, decreased in the order of AA-grafted film > one-step sample > two-step sample > NIPAAm-grafted film. The water absorbency steeply decreased at 20 to 40°C with increasing temperature when immersed in water at the temperatures (5–60°C) for 24 h. Thermosensitivity, which was defined as the ratio of water absorbencies of the grafted samples at 5 and 60°C, was higher for the one-step sample than the two-step one. The different extent of the water absorbency and the thermosensitivity between both samples is discussed in terms of location of grafted chains in the film substrate, which was determined by electron probe microanalysis and attenuated total reflection–infrared measurements, and monomer sequence distribution of the grafted chains. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2057–2064, 1998     

Surface photografting initiated by benzophenone in water and mixed solvents containing water and ethanol

Photografting reactions are usually carried out in organic solvents due to the water insoluble nature of photoinitiators such as benzophenone (BP). This work reports the effect of water and mixed solvents containing water and ethanol on the surface photografting of methacrylic acid (MAA) onto polyethylene initiated by BP. The percent grafting increased with the increase of water volume ratio in the mixed solvent, and BP showed the highest photoinitiation efficiency when dissolved in pure water solvent. Effects of BP concentration, monomer concentration, and monomer type on photografting were studied. The percent grafting showed the maximum at a lower BP concentration (0.20 mol/mol %) in pure water solvent than that (0.60 mol/mol %) in the mixed solvent with 90 v/v % water. The percent grafting first increased with the increase of monomer concentration till 3 mol L^?1 and then decreased. Acrylic acid (AA) could also be photografted onto polyethylene by BP in the mixed solvents. UV–visible spectroscopic examinations revealed that the λ_max of π–π* transitions of BP red shifted as the increase of the water volume ratio, i.e., the polarity of the solvent. The excitation of BP in solvents with a higher polarity under UV irradiation requires less energy, so the photografting initiated by BP is easier to occur. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improvement of autohesive and adhesive properties of polyethylene plates by photografting with glycidyl methacrylate

Glycidyl methacrylate (GMA) was photografted with the low‐ and high‐density polyethylene (LDPE and HDPE) plates to provide their surfaces with autohesive and adhesive properties. The chemical composition and wettability of the GMA‐grafted LDPE and HDPE (LDPE‐g‐PGMA and HDPE‐g‐PGMA) plates remained constant above full coverage of the surfaces with grafted PGMA chains. Autohesive strength obtained with 1,4‐dioxane as a good solvent of PGMA increased with an increase in the grafted amount and substrate breaking was observed at the grafted amount of 117 μmol/cm². The grafted amount at substrate breaking was decreased by increasing the temperature and load during heat pressing. Adhesive strength was effectively enhanced by use of multi‐functional amine compounds because of the increase in the reaction between primary or secondary amine groups and epoxy groups appended to the grafted PGMA chains. In addition, the decrease in the amine compound concentration and the increase in the number of amino groups in the amine compounds used led to the decrease in the grafted amounts at substrate breaking. Substrate breaking occurred at lower grafted amounts for the HDPE‐g‐PGMA plates than for the LDPE‐g‐PGMA plates because the location of the photografting was restricted to the outer surface region for the HDPE plate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 493–500, 2007     

X-Ray photoemission study of plasma modified polyethylene surfaces

X-Ray photoelectron spectroscopy (XPS) was used to determine plasma induced chemical species on the surface of polyethylene (PE). Argon plasmas were found to have no detectable chemical effect on the PE surface, whereas oxygen and nitrogen plasmas created new chemical species which altered the chemical reactivity of the PE surface. Oxygen plasmas were found to react more rapidly with the PE surface than nitrogen plasmas. The degree of incorporation of new chemical species in the near surface region is approximately 20 at. % at the saturation level for both oxygen and nitrogen plasmas. Core level spectra for oxygen and nitrogen plasma treated PE suggest the formation of primarily C-O-C species in the former and C-N species in the latter. Angle-resolved XPS measurements indicate that the depth of incorporation of new chemical species is confined to the top 25 A.     

Photografting of acrylic acid on high density polyethylene powder in vapour phase

A photografting technique was explored as a means of functionalizing high density polyethylene (HDPE) powder. The graft copolymerization reaction of acrylic acid on HDPE powder and the surface structure of grafted HDPE powder were studied in terms of grafting degree and grafting efficiency, and by FTIR and ESCA. The results show that the surface of chemically inert HDPE powder pretreated by an acetone solution of benzophenone (BP) can be graft‐copolymerized with acrylic acid by photografting in the vapour phase. Thereby, the grafting degree is increased but the grafting efficiency is decreased with increasing reaction time. When the BP concentration in pretreatment solution is increased, the grafting degree is increased to a maximum, and is then reduced. The most suitable reaction temperature is 90 °C. Grafting degree can reach the quite high value of 10.6 wt% under the conditions of BP concentration 1.0 wt%, reaction time 1 h and temperature 90 °C. © 2000 Society of Chemical Industry     

Surface photografting polymerization of vinyl acetate (VAc), maleic anhydride,and their charge transfer complex. I. VAc(1)

Photografting of vinyl acetate (VAc) onto LDPE films was carried out with lamination technology and simultaneous method, using BP as photoinitiator. Some principal factors affecting the grafting polymerization were investigated in detail. The experimental results showed that oxygen dissolved in monomer solution had great influence on grafting polymerization. Compared with other routine monomers (St, MMA, AN, AA, and AAm), VAc exhibited higher photografting reactivity. It was observed that the reaction temperature affected the graft polymerization markedly. To film samples with a given diameter, there exists optimum thickness of monomer solution. Adding a pertinent amount of water to the photografting polymerization system could accelerate the polymerization. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1513–1521, 2000     

Structure and adhesion properties of acrylic acid grafted high‐density polyethylene powders synthesized by a novel photografting method

A novel photografting, nonvapor, and nonliquid phase living graft polymerization was developed to functionalize high‐density polyethylene (HDPE) powder. The structure and adhesion properties of HDPE powder grafted with acrylic acid (AA) were studied by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), water contact angle, peel strength, and graft degree measurements. The result shows that HDPE powder can be grafted with AA via the method with a short reaction time and a high monomer conversion. The graft degree increases with the reaction time. Then, the hydrophilicity of the grafted HDPE powder increases also. The peel strength of HPDE/steel joint improved significantly when acrylic acid grafted HPDE powder was used as hot melt adhesive in place of ungrafted HDPE powder. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface photografting polymerization of trimethylolpropane triacrylate onto LDPE substrate in tetrahydrofuran/water mixtures

A surface photografting polymerization (λ > 300 nm) of a multifunctional monomer which was trimethylolpropane triacrylate (TMPTA), was conducted with benzophenone (BP) as photoinitiator and LDPE as model substrate, in mixed solvents containing tetrahydrofuran (THF) and water. Proved by ATR‐IR, highly crosslinked grafted layer was generated rapidly under UV irradiation. Effects on percent conversion of grafting are detailed with, such as feed ratio of BP to TMPTA, mass percent of TMPTA in the reaction system, mass percent of water in the mixed solvents and addition of the second monomer, methyl methacrylate (MMA). As both verified by SEM and AFM, relatively planar grafted layer was produced when photografting was carried out merely in THF; adding water in the reaction system caused the formation of “craters” in the grafted layer. In addition, effects of mass percent of water in the mixed solvents, UV irradiation time, TMPTA concentration and addition of MMA on the size, shape and quantity of the “craters” were investigated by SEM. A plausible mechanism for the formation of “craters” is also proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007