Photoinitiated surface grafting of synthetic fibers,I. Photoinitiated surface grafting of ultra high strength polyethylene fibers

Photoinitiated surface grafting of acrylic monomers has been carried out onto high strength polyethylene (HSPE) yarn by means of a continuous process. The grafting reaction is initiated by UV irradiation of the yarn after presoaking in an acetone solution of initiator and monomer. Four initiators, benzophenone (BP), 4-chlorobenzophenone (4-CBP), 2-hydroxy-2-cyclohexylacetophenone (HHA), and 2,2-dimethoxy-2-phenylacetophenone (DMPA), and two monomers, acrylic acid (AA) and acrylamide (AM), have been used. After short irradiation time (10 to 20 s) successful grafting is obtained, as shown by ESCA and IR-ATR spectra, dye adsorpotion from aqueous solution, and measurements of adhesion of single filaments to epoxy resin. Grafting efficiency of 74% has been reached for AA as monomer (26% is homopolymer). The tensile strength and modulus of the HSPE yarn are retained in the grafting process. The degree of surface grafting is mainly a function of structure and concentration of monomer and photoinitiator in the presoaking solution and of the irradiation conditions used. Increasing irradiation time gives increasing amounts of grafted polymer up to a certain limiting value. The reactivities of the four initiators have been compared showing the highest grafting yields of AA with BP and of AM with 4-CBP as photoinitiator. AA grafted HSPE yarn can be dyed to rather deep color by dipping in an aqueous solution of Crystal Violet. Increased dye absorption by a factor of up to seven has been measured for yarn grafted with AA to the maximum level obtained. The filaments of the grafted yarn show increased adhesion to epoxy resin by a factor of up to five compared with the ungrafted filaments.     

Photoinitiated surface grafting of synthetic fibers,IV. Applications of textile dyes onto surface-photografted synthetic fibers

High-strength polyethylene (HSPE), polypropylene (PP), poly(ethylene terephthalate) (PET), and poly(vinyl alcohol) (PVA) textile yarns have been surface-photografted with various functional monomers, such as acrylic acid (AA), acrylamide (AM), glycidyl acrylate (GA) and 4-vinyl pyridine (VP), by means of the continuous presoaking process developed. The dyeing of these surface-modified yarns with various textile dyes has been investigated. In general, considerable improvements of dyeability have been observed. The dye adsorption of the surface-photografted fibers is influenced by many factors, such as type of fiber, amount and properties of the functional monomer grafted on the surface of the fibers, type of textile dye, etc. The fibers surface-grafted with a monomer containing basic groups, such as acrylamide and 4-vinyl pyridine, are efficiently dyed with an acid dye. Conversely, a fiber surface-grafted with acidic functional monomer is easily dyed to deep shades with basic dyes. The dye adsorption increases monotonically with increasing grafting measured in ESCA spectra as relative intensities of relevant lines. The ungrafted HSPE, PP and PET fibers can be dyed to some extent with certain dyes. In the present work, the dye adsorption increased by 3.4 times for HSPE fiber grafted with GA and dyed with the metal complex dye IO, by 7.9 times for PP fiber grafted with AA and dyed with the basic dye MB, by 6.1 times for PET with AM and with the direct dye SL, and by about 15.3 times for PVA with VP and with the acid dye TE.     

Radiation grafting to poly(ethylene terephthalate) fibres

Polyethylene terephthalate (PET) monofilaments were grafted with styrene in methylene chloride solution using both the mutual and preirradiation methods. Good yields were obtained, the grafted fibres were dissolved and the graft copolymer and both homopolymers separated by various techniques. The graft copolymers were hydrolysed with potassium hydroxide in benzyl alcohol to destroy the PET backbone. The molecular weights were determined by osmometry. The G values of grafted side chains were 0.57 and 0.10 per 100 eV for the mutual and preirradiation methods, respectively. The corresponding fractions of PET grafted were 0.24 and 0.11. Less than 4% homopolymer was produced by either method. The yields contrast with radical yields measured by e.s.r. of only 0.025. It is suggested that the high grafting yields are due to the methylene chloride facilitating the accessibility of the monomer to the active sites created by the radiation rather than by the increased yields of radicals by chain transfer. Chlorine, for example, did not lead to increased yields even in the presence of methylene chloride. Presumably, in the mutual grafting system, radicals are available for grafting, which are too labile to be detected by e.s.r. In the case of the preirradiation method, the yields are also higher than the radical yields. This may be due to a regenerative chain transfer mechanism.     

Radiation grafting of N,N-dimethylaminoethylmethacrylate onto poly(ethylene terephthalate)

Summary Radiation-induced graft polymerization of N,N-dimethylaminoethylmethacrylate (DMAEMA) from 50% solution in chloroform onto poly(ethylene terephthalate) (PET) was carried out by means of mutual γ-irradiation of polymer in presence of liquid or vapor phase monomer solutions (direct method), or by grafting of monomer from this liquid solution onto polymer preirradiated in air. It has been shown higher effectiveness of grafting by the direct method from vapor phase of monomer or by the preirradiation method as compared with direct grafting from liquid monomer solution. Grafting did not affect crystallinity, transparency and durability of the starting PET. Received: 18 November 1999/Revised version: 7 February 2000/Accepted: 8 February 2000     

Hydrogen peroxide initiated grafting of acrylamide onto poly(ethylene terephthalate) fibers in benzyl alcohol

The grafting of acrylamide onto poly(ethylene terephthalate) fibers using hydrogen peroxide as the redox initiator was investigated. Benzyl alcohol was found to be the favorite medium for this grafting. Maximum graft yield (7.6%) was reached at 95°C; the graft yield decreased at higher temperatures, and finally grafting was inhibited at 120°C. The effect of monomer and initiator concentration on grafting was also studied. © 1996 John Wiley & Sons, Inc.     

Photochemical surface modification of poly(ethylene terephthalate)

To elucidate the role of chemical interactions in the promotion of metal–polymer adhesion, a poly(ethylene terephalate)/copper system was studied. Surface photografting of unsaturated monomers containing different chemical functional groups onto a three-mil poly(ethylene terephthalate) film provided a means of examining a variety of copper-polymer interfaces. Initial graft verification was accomplished via contact angle measurements. Adhesion strengths to vacuum-deposited copper were determined using 90° peel tests. Graft analysis, as well as investigation of the interfacial interaction between copper and the grafted moieties, was accomplished using X-ray photoelectron spectroscopy.     

Poly(ethylene terephthalate)/polypropylene microfibrillar composites. III. Structural development of poly(ethylene terephthalate) microfibers

Poly(ethylene terephthalate) was extruded, solid‐state‐drawn, and annealed to simulate the structure of poly(ethylene terephthalate) microfibers in a poly(ethylene terephthalate)/polypropylene blend. Differential scanning calorimetry and wide‐angle X‐ray scattering analyses were conducted to study the structural development of the poly(ethylene terephthalate) extrudates at different processing stages. The as‐extruded extrudate had a low crystallinity (～ 10%) and a generally random texture. After cold drawing, the extrudate exhibited a strong molecular alignment along the drawing direction, and there was a crystallinity gain of about 25% that was generally independent of the strain rates used (0.0167–1.67 s^?1). 2θ scans showed that the strain‐induced crystals were less distinctive than those from melt crystallization. During drawing above the glass‐transition temperature, the structural development was more dependent on the strain rate. At low strain rates, the extrudate was in a state of flow drawing. The resultant crystallinity hardly changed, and the texture remained generally random. At high strain rates, strain‐induced crystallization occurred, and the crystallinity gain was similar to that in cold drawing. Thermally agitated short‐range diffusion of the oriented crystalline molecules was possible, and the resultant crystal structure became more comparable to that from melt crystallization. Annealing around 200°C further increased the crystallinity of the drawn extrudates but had little effect on the texture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 137–146, 2007     

Improved mechanical properties of poly(ethylene terephthalate) nanocomposite fibers

Improvements in Young's modulus and strength (tenacity) of poly(ethylene terephthalate) (PET) fibers were obtained by drawing unoriented nanocomposite filaments containing low concentrations (<3 wt%) of various organically modified montmorillonites (MMTs) in a second step at temperatures above the glass transition. Prior to melt spinning, solid‐state polymerization was used to rebuild lost molecular weight, due to MMT‐induced degradation, to a level suitable for producing high strength fibers. Greater improvements in mechanical properties occurred when the MMT stacks were intercalated with PET. A nominal 1 wt% loading of dimethyl‐dehydrogenated tallow quaternary ammonium surface modified MMT in drawn PET fiber showed a 28% and 63% increase in Young's modulus and strength, respectively. Relative to an unfilled PET fiber, these results surpassed the upper bound of the rule of mixtures estimate and suggested that both the type of surface modification and concentration of MMT affect the degree of PET orientation and crystallinity. Furthermore, drawability above T_g and elongation at break increased upon the addition of organically modified MMT to unoriented PET fibers, which was a key distinction of this work from others examining similar systems. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Composition depth profiles of plasma-fluorinated poly(ethylene terephthalate) fibers

Composition depth profiles of the outer 50 Å of plasma-fluorinated poly(ethylene terephthalate) fibers were obtained by angle-dependent X-ray photoelectron spectroscopy (XPS). The effect of sample geometry on XPS sampling depth and the depth distribution function (DDF) was determined theoretically for cylindrical and hemispherical surfaces. The theoretical DDFs are nonexponential. For cylindrical surfaces, the effect is small, a 22% increase in surface sensitivity. The average XPS sampling depth for smooth, properly oriented fibers is shown to vary, as it does for a planar surface, as the sine of the nominal takeoff angle. The DDF appropriate for cylindrical surfaces was incorporated into a computer program for inversion of angle-dependent XPS data to obtain composition depth profiles of the fibers. Plasma-fluorinated PET fibers were used to demonstrate the use of angle-dependent XPS on fibers. XPS results indicate that most fluorination occurs within the top few “monolayers,” attack is preferentially at the phenyl ring, both ? CHF? and ? CF₂ ? moieties are formed, and fluorination causes partial loss of aromaticity. © 1994 John Wiley & Sons, Inc.     

Lamellar structure and properties in poly(ethylene terephthalate) fibers

The fibrillar and the lamellar structures in a range of poly(ethylene terephthalate) fibers were studied by small-angle X-ray scattering. The intensity maxima in the lamellar peaks lie on a curve that can be described as an ellipse. Therefore, the two-dimensional images were analyzed in elliptical coordinates. The dimensions of the coherently diffracting lamellar stack, the dimensions of the fibrils, the interfibrillar spacing, and the orientation of the lamellar surfaces were measured in addition to the lamellar spacing. The orientation of the lamellar planes and the size of the lamellar stacks had a better correlation with mechanical properties of the fibers than did the lamellar spacing. In particular, longer and wider lamellar stacks reduced fiber shrinkage, as did the closer alignment of the lamellar normal to the fiber axis. These structural features were also associated with lower tenacity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2527–2538, 1998     

Aspects of the yield behavior in poly(ethylene terephthalate) fibers

The yield behavior during cold drawing of commercially spun poly(ethylene terephthalate) (PET) filament yarn was investigated. Microscopic examination revealed the presence of inherent flaws within the spun filaments; these act as points for localized stress concentration. These inhomogeneities appear to be either internal cracks or crazes developed during the fiber melt spinning process. During elongation, stress magnification at these flaws results in shear band formation, indicating the onset of inhomogeneous yielding. At the yield bend in the load-elongation curve a circumferential crack propagates within these shear band regions. This yield crack develops into the classical neck geometry which further localizes additional plastic deformation within the sample at the neck.     

Benzoyl-peroxide-initiated graft copolymerization of poly(ethylene terephthalate) fibers with acrylamide

In this study the grafting of acrylamide onto poly(ethylene terephthalate) fibers with the help of benzoyl peroxide and the effects of the temperature and the concentrations of initiator and monomer were investigated. Some of the experiments were repeated several times in order to check the reproducibility. The optimum temperature for grafting was found to be 75°C. The graft yield was observed to increase with the monomer concentrations examined. The graft yield increased up to the benzoyl peroxide concentration approximately 0.05 g/50 mL, and then passed a plateau, before showing a decrease. The fiber diameter, intrinsic viscosity, and the moisture regain increased while the fiber density decreased with the graft yield.     

Superstructure in ultrahigh speed spun fibers of poly(ethylene terephthalate)

Ultrahigh speed spinning of poly(ethylene terephthalate) (PET) was carried out at various take-up velocities from 5 to 10 km/min. The superstructure of as-spun fibers was characterized by small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), viscoelastic properties, and scanning electron microscopy (SEM). Above 6 km/min the peaks or shoulders that are due to the interference between microfibrils appear on the equatorial SAXS intensity curves. The interfibrillar spacing estimated from the peak position increases with increasing take-up velocity. Comparison of the spacing with the lateral crystal sizes estimated from the broadness of the crystal (hk0) WAXD peaks indicates that the microfibril diameter becomes thick with increasing take-up velocity. Although the orientation and density in amorphous region for high-speed spun fibers are very low on the average, it can be seen that a few highly extended tie molecules exist in that region, and the number of these molecules increases with increasing take-up velocity. The modes and mechanisms of fibrillation induced by a rubbing test are discussed relating to these results.     

Mechanism of cold drawing in melt-spun poly(ethylene terephthalate) fibers

An investigation has been made into the mechanism of cold drawing in melt-spun poly(ethylene terephthalate) (PET) fibers. An analysis of the cold-drawing behavior using wide-angle x-ray diffraction, orientation measurements, calorimetric and mechanical techniques was performed. The evidence suggests that the cold-drawing process involes stress-enhanced crystallization which occurs in conjuction with incresing orientation of the crystalline and amorphous regions. A degradation in the fiber properties after cold drawing was observed for fibers spun below 1,000 m/min while fibers spun above 1,000 m/min exhibited an improvement in fiber properties with cold drawing. This behavior was explained by the existence of two distinct irreversible deformation micromechanisms for fibers spun below and above 1,000 m/min.     

Orientation-induced crystallization of poly(ethylene terephthalate) fibers with controlled microstructure

Orientation-induced crystallization of PET fibers was studied by the in-situ wide-angle X-ray diffraction (WAXD) utilizing synchrotron radiation source combined with thermomechanical analysis. The noncrystalline as-spun fiber spun was heat-treated at 150, 165, 180 and 195 °C for 0.1 s under constrained condition. The heat-treatment allowed the fibers to have various amount of isotropic amorphous (IA), oriented noncrystalline (ON), and crystalline (Cr) phase. The structure evolution accompanying the crystallization of the fibers was then examined upon elevating temperature while the fiber length was held constant. The X-ray results clearly showed that the crystallization takes place first by ON phase (extended-chain crystallization) and then followed by the crystallization of IA phase (folded-chain crystallization). The on-set of extended-chain crystallization was dependent on the amount and degree of orientation of ON phase in the fiber that was derived from the various heat-treatment temperatures. It is also noted that the IA phase transforms into not only the CR phase but also the ON phase. The crystallization on the surface of preformed extended-chain crystals appeared to induce the spontaneous orientation of the chains. The thermomechanical data indicated that a stress emerges rapidly on fiber above glass transition temperature (T_g), which is associated with the entropic relaxation of the ON phase. The stress emerged on fiber then dropped drastically as the temperatures of fibers reached the temperatures of extended-chain crystallization, indicating that the stress drop is closely related with the extended-chain crystallization. The fibers heat-treated at the highest temperature showed the highest initial crystallinity but showed the slowest crystallization rate, resulting in the lowest final crystallinity among the fibers.     

The fracture toughness of polypropylene containing poly(ethylene terephthalate) fibers

The fracture toughness of polypropylene was increased tenfold by the addition of 30 volume percent of chopped poly(ethylene terephthalate) rovings without any appreciable sacrifice in strength or modulus. The resulting fracture toughness was independent of temperature to ?40°C. For maximum effectiveness the rovings must be integrated so that the component filaments cannot disperse during the processing and injection molding stages. The three different methods employed to measure fracture toughness showed good correlation with each other and confirmed the general utility of the Izod test (with slight modification) as a measure of fracture energy. The increased toughness was attributed almost entirely to frictional energy losses during fiber pullout. Polyester fibers can be useful additives for increasing the fracture toughness of brittle resins where processing temperatures do not preclude their use.     

Solvent-induced structural changes in sulfonated poly(ethylene terephthalate) (SPET) fibers

The microstructure and macrostructure of sulfonated poly(ethylene terephthalate) (SPET) fibers were studied by subjecting them to solvents with solubility parameters similar to those of the PET. Dimethyl sulfoxide (DMSO), methylene chloride (MeCl₂), and pyridine, whose solubility parameters (δ) are close to those of the flexible aliphatic ester segment (? CO? O? CH₂? CH₂), the semirigid aromatic segment (? CO? C₆H₄), and the average δ of the PET repeating unit, respectively, were used. The solvent uptake levels of these three solvents, which were not affected by crimping or relaxing processes of the fibers, were related to their sizes, shapes, and solubility compatibility with SPET. The solventinduced effects were strongly dependent upon the fiber structure caused by the fiber-forming processes, but were generally not as strong as the processes. The most distinct changes brought about by the solvents include overall orientation determined by birefringence and the trans–gauche ratio and extent of chain fold by FTIR measurements. © 1994 John Wiley & Sons, Inc.     

Blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Commercial grade poly(ethylene terephthalate), (PET, intrinsic viscosity = 0.80 dL/g) and poly(butylene terephthalate), (PBT, intrinsic viscosity = 1.00 dL/g) were melt blended over the entire composition range using a counterrotating twin‐screw extruder. The mechanical, thermal, electrical, and rheological properties of the blends were studied. All of the blends showed higher impact properties than that of PET or PBT. The 50:50 blend composition exhibited the highest impact value. Other mechanical properties also showed similar trends for blends of this composition. The addition of PBT increased the processability of PET. Differential scanning calorimetry data showed the presence of both phases. For all blends, only a single glass‐transition temperature was observed. The melting characteristics of one phase were influenced by the presence of the other. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 75–82, 2005