IGC Characterization of PMMA Grafted onto CTMP Fiber

Inverse Gas Chromatography (IGC) was used to characterize chemithermomechanical pulp (CTMP) wood fiber surfaces modified by polymer grafting. From the retention times at infinite dilution over a range of temperatures, the differential heat of adsorption, ΔH^oA, the standard free energy, ΔG^oA, and the standard entropy of adsorption, ΔS^oA, have been determined for the n-alkanes vapors C₈-C₁₁ on CTMP wood fibers grafted with poly(methylmethacrylate) (PMMA) at various polymer loadings (PL). The dispersive component of the surface free energy γ^LS (London) has also been calculated by using a method based on the increment of ΔG^oA per CH₂ group. Comparison of results for the original material, CTMP and PMMA, with those of the grafted fibers has allowed the evaluation of surface modification. Grafted samples at high PL show values of ΔH^oA, ΔG^oA, and γ^LS approaching those of the pure PMMA indicating a high density of polymer chains grafts on the CTMP wood fiber.     

Surface analysis by ESCA of sulfite post-treated CTMP

Handsheets of post-treated chemithermomechanical pulps (CTMP) and a sample of Whatman paper no. 1 were analyzed using an ESCA spectrometer. All of these samples revealed the presence of the C₁, C₂, and C₃ components in the carbon (1s) peak and the O₂ component in the oxygen (1s) peak; the O¹ peak component which was present in the other samples was missing from the Whatman paper. Pulp sulfonation produced a reduction in C₁ representing the group of carbon not bonded to oxygen, and an increase in C₂ with C₃ remaining relatively constant. These changes imply reductions in lignin and extractives and a corresponding increase in cellulose content on the fiber surface. Extrapolation of the C₁, C₂, C₁/C₂, and O/C curves of CTMP to zero percent sulfonation yielded the same values as those obtained for pure TMP. ESCA analysis allows us to monitor the increase of sulfur content as a function of sulfonation in accordance with results obtained from bulk pulp sulfonate content titration.     

ESCA study of the solid residues of supercritical extraction of Populus tremuloïdes in methanol

A systematic ESCA study of the solid residues of supercritical critical extraction of Populus tremuloïdes prepared in various conditions has been performed. Reference materials also examined by ESCA included the initial wood, Whatman no. 1 paper, and two lignins prepared by different procedures. Interest has been focused on the C_ls and O_ls spectra and on the determination of surface O/C atomic ratio. A difference between bulk O/C values measured by chemical analysis and surface O/C ratios obtained from ESCA data is considered diagnostic of a difference in chemical composition of the bulk and the surface. In the C_ls peaks of wood and its constitutive polymers, the usual components peaks C₁, C₂, and C₃ were observed. For the solid residues, however, a fourth peak designated as C₀ appears, the importance of which increases steadily when the temperature of extraction is raised from 250 to 350°C. The component C₀ was ascribed to polyaromatic constituants. Its proportion is correlated with the fraction of the carbon in the residue comprised in the recondensed material and determined independently. The O_ls peak shows also a complex structure with three components in the wood-derived reference materials and four in some of the solid residues. These structures have not been discussed previously in the literature and a tentative assignment for the component peaks is proposed.     

Graft copolymerization of methyl methacrylate onto rubber‐wood fiber using H2O2 and Fe2+ as an initiator system

Methyl methacrylate (MMA) was successfully grafted onto rubber‐wood fiber in a free‐radical solution polymerization initiated by ferrous ion and hydrogen peroxide. The effects of the reaction parameters (reaction temperature, reaction period, influence of hydrogen peroxide, ferrous ammonium sulfate, and monomer concentrations) were investigated. The grafting percentage showed dependency on H₂O₂, Fe²⁺, and monomer concentrations, as well as reaction temperature and reaction period. The optimum reaction temperature was determined to be about 60°C and the reaction period was 60 min. The optimum concentration of H₂O₂ was 0.03M and optimum amounts of Fe²⁺ and MMA were 0.26 mmol and 2.36 × 10^?2 mol, respectively. Poly(methyl methacrylate) (PMMA) homopolymer was removed from the graft copolymer by Soxhlet extractor using acetone. The presence of PMMA on the fiber was shown by FT‐IR spectroscopy and gravimetric analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2499–2503, 2003     

Photoinitiated surface grafting of synthetic fibers,III. Photoinitiated surface grafting of poly(ethylene terephthalate) fibers

Photoinitiated surface grafting of acrylic acid (AA), acrylamide (AM) and 4-vinyl pyridine (VP) onto poly(ethylene terephthalate) (PET) fibers (a commercial textile yarn) has been studied using benzophenone (BP) as photoinitiator. A continuous process as previously described has been applied, which involves presoaking of the PET yarn in a solution of initiator and monomer in acetone and UV irradiation in nitrogen atmosphere. The resulting grafted polymer on the fiber surface has been analyzed by ESCA, titration of carboxy groups (grafted AA), and dye absorption. The relative ESCA intensities (RI) of O1s/C1s and N1s/C1s are used as measure for grafted AA, AM and VP, respectively, after recording the RI-values for ungrafted fibers. For grafting with AA, the RI-values increased from 32.8% (background) to 48.6% after 20 s irradiation time. The amount of carboxy groups measured by titration increased from 0.045 to 0.106 mmol/m². Assuming an even coverage of grafted AA polymer, this means a grafted layer of 4.8 nm thickness. After grafting, the adsorption of the dye Crystal Violet (CV) from aqueous solution increased by about 3 times. With AM as monomer, the RI-values increased from 2.6 (background) to 14.8% and the adsorption of a direct dye Sirius Lichtbordo B-LL increased by about 6 times. With VP as grafted monomer, the RI-values increased from about 2.6 (background) to 5.1% and the adsorption of the direct dye increased by about 4 times.     

Surface graft copolymerization of 2‐hydroxyethyl methacrylate onto low‐density polyethylene film through corona discharge in air

The corona discharge technique was explored as a means of forming chemically active sites on a low‐density polyethylene (LDPE) film surface. The active species thus prepared at atmospheric pressure in air was exploited to subsequently induce copolymerization of 2‐hydroxyethyl methacrylate (HEMA) onto LDPE film in aqueous solution. The results showed that with the corona discharge voltage, reaction temperature, and inhibitor concentration in the reaction solution the grafting degree increased to a maximum and then decreased. As the corona discharge time, reaction time, and HEMA concentration in the reaction solution increased, the grafting degree increased. With reaction conditions of a 5 vol % HEMA concentration, 50°C copolymerization temperature, and a 2.0‐h reaction time, the degree of grafting of the LDPE film reached a high value of 158.0 μg/cm² after treatment for 72 s with a 15‐kV voltage at 50 Hz. Some characteristic peaks of the grafted LDPE came into view at 1719 cm^?1 on attenuated total reflectance IR spectra (C?O in ester groups) and at 531 eV on electron spectroscopy for chemical analysis (ESCA) spectra (O_1s). The C_1s core level ESCA spectrum of HEMA‐grafted LDPE showed two strong peaks at ～286.6 eV (? C ? O? from hydroxyl groups and ester groups) and ～289.1 eV (O?C ? O? from ester groups), and the C atom ratio in the ? C? O? groups and O?C? O groups was 2:1. The hydrophilicity of the grafted LDPE film was remarkably improved compared to that of the ungrafted LDPE film. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2881–2887, 2001     

Photooxidation of the surfaces of polyphenylene oxide and polysulfone

Changes in the composition and structure of the surfaces of polyphenylene oxide (PPO) and polysulfone caused by UV photooxidation are followed using ESCA. The surface stoichiometry of PPO changes from C₈O₁ to C₈O_4.8 on photooxidation, the oxygen being added in the form of carbonyl and especially carboxyl groups. Surface photooxidation is rapid, the ESCA spectra showing substantial changes after a few minutes of irradiation, and no further changes being detected after 10 h of reaction. The surface photooxidation of polysulfone occurs in three stages. In the first 2 h rapid oxidation takes place at carbon atoms, the levels of C—O, carbonyl, and carboxyl groups increasing at comparable rates. This is followed by slower oxygen incorporation up to 15 h of reaction, during which time carbonyl and carboxyl levels increase and oxidation of the sulfone sulfur is observed. Some degradation occurs as groups containing carbon and oxygen are lost from the surface. Further oxidation then produces a decrease in the surface levels of C—O and carbonyl groups, and further degradation. The photooxidized surface has a stoichiometry of C₁₀O₆S, compared with C₂₇O₄S in the unreacted polymer.     

Studies on preparation of PGMA/Al2O3 and its effect on impact strength of epoxy resin

In this article, two kinds of methods for grafting polyglycidyl methacrylate (PGMA) onto Al₂O₃ surface by the radical polymerization initiated by peroxide groups and double bond groups, respectively, were investigated. In the first method, peroxide groups, as initiators, were immobilized onto the Al₂O₃ surface. Then, GMA was polymerized on Al₂O₃ under the radicals decomposed by peroxide groups, and PGMA was grafted onto Al₂O₃. But in the second method, 3‐methacryloylpropyl trimethoxysilane was chemically bonded onto the Al₂O₃ surfaces firstly to introduce double bonds. Secondly, the copolymerizations between the immobilized double bonds and the monomer GMA were performed, homopolymerizations of GMA followed, and finally PGMA was grafted to the Al₂O₃ surfaces. The effects of grafting methods on grafting degree were examined mainly. At the same time, the effects of different grafting conditions on the grafting degree were researched. Furthermore, the effect of the grafted particles PGMA/Al₂O₃ on impact strength of the epoxy composites was studied. It was found that the grafting degree achieved by the first method was much higher than that by the second, and the grafting degree can reach about 54%. Moreover, the impact strength of epoxy composites containing PGMA/Al₂O₃ particles were improved largely, and which increased with the grafting degree. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of a carbon nanotube/carbon fiber multi-scale reinforcement by grafting multi-walled carbon nanotubes onto the fibers

To prepare a carbon nanotube (CNT)/carbon fiber multi-scale reinforcement (MSR), multi-walled carbon nanotubes (MWCNTs) functionalized at the end caps with hexamethylene diamine (HMD) are grafted onto the surfaces of carbon fibers treated with acyl chloride. The surface element concentrations, surface functional groups and morphology of the MSR were examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS spectra indicate that sp² and sp³ carbon atoms are major components in the MSR surface, and the carbon fiber surface structure is not destroyed. There is 17.41% of C-NH_x in the surface of the MSR, which suggests that MWCNTs are covalently grafted onto carbon fiber surfaces. SEM shows that the grafted MWCNTs stick to the carbon fiber surface at different angles, and are uniformly distributed along the outer edges of the grooves in the fiber surface. The grafted MWCNTs are 50-200 nm in length and around 14 nm in diameter. It was found that the grafting increases the weight of carbon fiber by 1.2%, which implied that a considerable amount of MWCNTs were grafted onto carbon fiber surfaces.     

Functional biohybrid materials synthesized via surface-initiated MADIX/RAFT polymerization from renewable natural wood fiber: Grafting of polymer as non leaching preservative

Crude wood fibers represent a wide class of renewable resources. The surface modification of such materials via covalent grafting of polymer offers new surface properties with non-leaching coating. The grafting of the polymer chains was achieved by surface-initiated controlled radical polymerization through a grafted xanthate chain transfer agent. Macromolecular design via interchange of xanthate (MADIX) technique was chosen to graft poly(vinyl acetate), polystyrene, poly(n-butyl acrylate) and poly(4-vinylbenzyl chloride)-polystyrene amphiphilic cationic copolymers. Water contact angle measurements highlighted the hydrophobization of the wood fiber surface with a nanoscaled polymer monolayer indicating the appropriate coverage of the fiber. X-ray photoelectron spectroscopy showed the successful grafting of the polymer after drastic washing procedure. The quaternization of the grafted polystyrene-co-poly(4-vinyl benzyl chloride) copolymers with tertiary amine allows the introduction of biocide quaternary ammonium functions while preserving the hydrophobic character of the modified wood fiber when introducing a long alkyl chain in the statistical copolymer. Finally, the cationic copolymer was subjected to Coniophora Puteana to evaluate its propensity to limit the fungi expansion.     

Solvent free vapour phase photografting of acrylamide onto poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) sheets were surface grafted with acrylamide under reduced pressure in a solvent free vapour of acrylamide and benzophenone. The grafting was initiated with UV irradiation and no pre-treatment of PMMA by impregnation or sorption of reactants was required. Characterization of grafted samples by ESCA and contact angles showed that the nitrogen content increased with grafting time and temperature. The surface bound amide groups obtained were converted into amine groups by the Hofmann reaction and used in coupling reactions with a p-nitrophenylcarbonate terminated PEG and 4,4,4-trifluoro butyraldehyde.     

The effect of moisture presoaking on graft copolymerization of methyl methacrylate in wood under mutual irradiation by electron beam accelerator

Polymerization of MMA was carried out in wood under mutual electron beam irradiation. The changes in molecular weight (M _n, M _m) and the number of polymer branches grafted to holocellulose and lignin were compared with the swelling degree (ΔL_H2O) of base veneers obtained by moisture presoaking before impregnation of the monomer. Increases in molecular weight as well as in the number of both grafted branches were observed with increase in ΔL_H2O up to ca. 4% in the lower range of ΔL_H2O. However, for the number of polymer branches grafted to holocellulose, the increse reached a peak at ΔL_H2O of ca. 4%, in contrast to the continuous increase of both molecular weights M _n and M _w. This is due to the bimolecular recombination-type termination of the propagating radicals mutually between those originating from the holocellulose and the irradiated MMA within the cellular parts or due to their termination onto lignin. The polymer branches grafted to lignin came from the latter termination, and it was found that the lower molecular weight branches grafted to lignin came from those propagating radicals which were produced from irradiated MMA in the void space and terminating onto lignin.     

Effect of fiber treatment on the mechanical properties of hybrid fiber reinforced polystyrene composites. Part II. Use of glass fiber and wood pulp as hybrid fiber

The mechanical properties of polystyrene reinforced with a mixture of hardwood aspen chemithermomechanical pulp (CTMP) and surface-treated glass fiber have been studied. The adhesion of cellulose fiber to glass fiber as well as to thermoplastics improved thanks to various surface treatments of CTMP, e.g. coating with polymer+isocyanate or with silane, and grafting with polystyrene. In general, compared with non-treated CTMP-filled composites, the mechanical properties improved when surface-treated wood fiber was used as a filler. Experimental results indicate better compatibility between treated wood fiber and surface-treated glass fiber as well as polystyrene and, consequently, the mechanical properties were enhanced.     

Grafting of vinyl polymers onto VGCF surface and the electric properties of the polymer-grafted VGCF

The graft polymerization of vinyl monomers onto vapor grown carbon fibers (VGCF) initiated by the system consisting of molybdenum hexacarbonyl (Mo(CO)₆) and trichloroacetyl (COCCl₃) groups introduced onto the surface was investigated. The introduction of trichloroacetyl groups onto VGCF surface was successfully achieved by the reaction of carboxyl groups on VGCF surface with trichloroacetyl isocyanate. It was found that the radical graft polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and glycidyl methacrylate (GMA) is successfully initiated by the system consisting of Mo(CO)₆ and COCCl₃ groups introduced onto the surfaces. In the polymerization, the corresponding vinyl polymers were effectively grafted onto the VGCF surface, based on the propagation of polymer from surface radicals formed by the interaction of trichloroacetyl groups and Mo(CO)₆: the percentage of PMMA grafting reached 40%. Polymer-grafted VGCF gave a stable colloidal dispersion in good solvents for grafted polymer. The electric resistance of composite prepared from the polymer-grafted VGCF suddenly increased in organic solvent vapor over 10³ times, and returned to initial resistance when it was transferred into dry air. These results indicate that such composites can be used as novel gas sensors.     

Synthesis of polysiloxane‐grafted fluoropolymers and their hydrophobic properties

A polydimethylsiloxane with an epoxide end group was grafted onto a fluoropolymer that had hydroxyl side chains by using protonic or Lewis acids as catalysts. Strong acids such as trifluoromethanesulfonic acid were found to be effective for the grafting of the polydimethylsiloxane of relatively large molecular weight (M_n 4440). A coating prepared from the graft polymer was so hydrophobic that a water droplet of 10 μL slid down on its inclined plane surface (30° with respect to the horizontal). ESCA analysis revealed that the siloxane branches are preferentially present on the surface. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1955–1963, 2000     

Novel vinyl-modified sepiolite-based polymer nanocomposites: synthesis and characterization

An environmental-friendly synthesis of polymer clay nanocomposites (PCNs) was carried out by incorporation of nanoclay into polymer matrix for their potential application as sorbent of metals present in aqueous media. Polyacrylonitrile was chemically grafted onto 77% vinyl triethoxysilane-modified sepiolite. The polymerization was carried out with benzoyl peroxide (BPO, C₁₄H₁₀O₄) initiator in three different weight ratios of 1.0, 2.0, and 3.0%. The maximum polymer grafting of about 83% was obtained in nanocomposite initiated by 2.0% ratio of BPO. The surface modification of nanocomposites was carried out using hydroxyl amine hydrochloride (NH₂OH·HCl). The prepared nanocomposites were characterized by Fourier transform infrared spectroscopy, X-ray diffractometry, thermogravimetric analysis, and Brunauer–Emmett–Teller technique. The copper removal tendency of nanocomposites was studied by atomic absorption spectroscopy. The maximum adsorption of copper was 86%, which could be achieved by nanocomposites synthesized with 2% initiator. The results have revealed the practical potential of the prepared PCN as efficient adsorbents.     

Supercritical CO2 assisted ternary-monomer grafting copolymerization of polypropylene

Free-radical grafting of ternary-monomer onto polypropylene (PP) particles in the solid state has been studied using supercritical carbon dioxide (SC CO₂) as a solvent and a swelling agent. The PP particles were first swelled with the monomers and AIBN as an initiator, using SC CO₂ at different experimental conditions of pressure, temperature and treatment time. After releasing CO₂, monomers were grafted onto PP in different temperatures. During monomer selection, combination of soft monomer and hard monomer was used in order to tune polarity and flexibility of grafted polymer. FTIR spectra confirmed that ternary-monomer had been grafted onto PP and SEM showed that grafted molecules had been uniformly distributed in the PP substrate. TG analysis indicated that thermal stability of grafting modified PP had been improved, and DSC revealed that grafting leads to a lower degree of crystallinity of polypropylene.     

ESCA analysis of partially converted lignocellulosic materials

Further ESCA data of the solid residues obtained by supercritical extraction of Populus tremuloides are reported. The changes of the ESCA spectra with the severity of grinding are discussed. These data allow us to draw precise conclusions on the spatial distribution of carbonaceous recondensed material as thermal conversion proceeds. The C_1s peaks are of special interest as the distribution of the four components in these peaks bears information on the nature of the chemical compounds present on the surface of the sample.     

Controlled atom transfer radical polymerization of MMA onto the surface of high-density functionalized graphene oxide

We report on the grafting of poly(methyl methacrylate) (PMMA) onto the surface of high-density functionalized graphene oxides (GO) through controlled radical polymerization (CRP). To increase the density of surface grafting, GO was first diazotized (DGO), followed by esterification with 2-bromoisobutyryl bromide, which resulted in an atom transfer radical polymerization (ATRP) initiator-functionalized DGO-Br. The functionalized DGO-Br was characterized by X-ray photoelectron spectroscopy (XPS), Raman, and XRD patterns. PMMA chains were then grafted onto the DGO-Br surface through a ‘grafting from’ technique using ATRP. Gel permeation chromatography (GPC) results revealed that polymerization of methyl methacrylate (MMA) follows CRP. Thermal studies show that the resulting graphene-PMMA nanocomposites have higher thermal stability and glass transition temperatures (T_g) than those of pristine PMMA.     

Surface modification of polyacrylonitrile (PAN) fibers by grafting of natural polymer-soybean protein (SP)

Summary A novel method of modifying polyacrylonitrile (PAN) fibers by grafting of soybean protein (SP) onto it was studied. The reactant of PAN-g-SP fiber was prepared based on chlorination of the hydrolyzed PAN fiber. The effects of chlorination and grafting conditions on the grafting efficiency were investigated. The grafting efficiency first increases with the increase of the addition of thionyl chloride (SOCl₂), chlorination time and temperature and then levels off. In grafting reaction, grafting efficiency increases at first and then declines significantly with increasing addition of sodium hydroxide (NaOH), grafting temperature and time. The grafted polymer was characterized by FT-IR spectroscopy, X-ray diffraction and SEM images. The results indicated that SP was grafted onto the PAN fiber. PAN-g-SP also exhibits good hygroscopicty and proper mechanical properties.