In situ cure monitoring of epoxy resins using fiber-optic Raman spectroscopy

Fiber-optic Raman spectroscopy was used to monitor the curing of epoxy resins in situ for eventual application to polymer composite processing. A 200-μm diameter quartz fiberoptic sensor immersed in liquid resin was used to obtain Raman spectra for a concentration series of diglicidyl ether of bisphenol-A in its own reaction product with diethylamine using an 820 nm continuous-wave diode laser excitation. A Raman peak at 1240 cm^?1 was assigned to a vibrational mode of the oxirane (epoxide) ring and its normalized intensity was found to be linearly related to the concentration of epoxide groups in the resin mixtures. Raman peaks at 1112 and 1186 cm^?1 associated with phenyl and gem-dimethyl resin backbone vibrations, respectively, did not change in intensity due to the curing reaction and were used as internal references to correct the Raman spectra for intensity changes due to density fluctuations and instrumental variations during the experiments. Fiber-optic Raman spectroscopy was used to monitor the extent of reaction in situ for the room-temperature cure of phenyl glicidyl ether with diethylamine. The extent of reaction of the epoxide groups calculated from the Raman spectra were in excellent agreement with kinetic data from Fourier transform near-infrared absorbance measurements made under the same conditions. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Cure of epoxy resins with aromatic amines: High heat-distortion studies

Castings having unexpectedly high heat-distortion temperatures result when certain treated resins of the EPON

1 EPON is a registered trademark of the Shell Oil Company.

828 type and about 75% of the stoichiometric amount of m-phenylenediamine, are postcured for 10–20 hr. at 175–200°C. The improvement in heat-distortion temperature is about 100°C., to values as high as 250°C. A recrystallized resin has given the highest values. Other glycidyl ethers of polyphenols have shown this phenomenon to a lesser degree, but other amine curing agents, including isomers and substitution products of m-phenylenediamine, have not. Some evidence of a new curing reaction has been developed, by NMR and pyrolysis studies of model compounds, which supports the postulate that the m-phenylenediamine is alkylated with a fifth epoxy group during the postcure, presumably at a ring carbon, resulting in greater crosslinking.     

Glass fiber-reinforced epoxy composites

Glass fiber-reinforced epoxy composites were prepared from the matrix resins tetraglycidyl diaminodiphenylmethane

1 Systematic name: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-4,4′-diaminodiphenylmethane.

(TGDDM) and tetraglycidyl bis(o-toluidino)-methane

2 Systematic name: N,N,N′,N′-Tetrakis(2,3-epoxypropyl)-4,4′-bis(o-toluidino)methane.

(TGMBT) using various amines like 4,4′-diaminodiphenylmethane (DDM), 4,4′-diaminodiphenylsulfone (DDS) and diethylene triamine (DETA) as curing agents. The fabricated laminates were evaluated for their mechanical and dielectrical properties and chemical resistance. The composites prepared using an epoxy fortifier (20 phr) showed significant improvement in the mechanical properties.     

Porous bead aliphatic-aromatic methacrylate copolymers,I. Effect of polymerization conditions on porous structure formation of methyl methacrylate — di(methacryloyloxymethyl)naphthalene copolymers

The influence of inert porogenic mixture and monomer mixture composition and concentration on specific surface areas, pore size distribution, volumes of pores capable of capillary condensation of nitrogen and true density of copolymers were investigated for a new type of methacrylate monomer system: methyl methacrylate and di(methacryloyloxymethyl)naphthalene. The obtained copolymers exhibit similar character as it is typical for PPS

1 PPS = Porous by Precipitant and Solvent.

styrene-divinylbenzene resins.     

Effects of water content on the properties of starch/poly(ethylene–vinyl alcohol) blends

The physical properties of unmodified starch, poly(ethylene vinyl alcohol), glycerol, and water mixtures are reported. Thermal and melt-flow properties of the preprocessed, physically mixed materials were determined along with the tensile properties and morphology of injection-molded microtensile samples. Melt-flow properties were measured by a capillary rheometer, and the water content was varied from 4 to 18%. The morphology, rheology, and tensile properties are all highly related to the percentage of water present. A transition in the tensile properties and morphology of the blends was observed at approximately 11% moisture content. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Investigation of primers reducing the pink-ring formation in multilayer printed circuit boards

A rapid and easy screening test was applied to assess the capability of various formulated primers to reduce the defect of pink rings in multilayer printed circuit boards. The mixtures of silanes with multifunctional silanol groups (crosslinkers) and 3-glycidoxypropyl-trimethoxysilane

1 Systematic name: 3-(2,3-Epoxypropoxy)propyl-trimethoxysilane.

(referred to as silane C) or N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane

2 Systematic name: 3-[N-2-aminoethyl]aminopropyl-trimethoxysilane.

(silane B) were proved to be effective in reducing the pink rings. The performance of the mixed silanes using silane A and crosslinkers with aromatic groups were better than other formulated primers which was partly attributed to less amounts of hydrophilic groups and better integrity in the primer films. A developed primer consisting of siloxane compounds had the best performance. The online test confirmed the results from the screening test and demonstrated the feasibility of the designed screening test in assessing the performance of primers. The results of FTIR spectroscopy and thermogravimetric analyses confirmed that the effective primers coated on the copper oxides could improve the curing reaction and the thermal oxidative stability of the epoxy/CuO system.     

Polyamine-modified urea–formaldehyde-bonded wood joints. III. Fracture toughness and cyclic stress and hydrolysis resistance

The objective of this study was to improve the durability and stability of urea–formaldehyde-bonded wood products by decreasing the internal stress developed during the resin cure and by improving the ability of the cured system to withstand cyclic stresses. Urea–formaldehyde resins were modified either by incorporating urea-capped di-and trifunctional amines into the resin structure or by using the hydrochloride derivatives of some of these amines as the curing agent, or by both methods. This study supplements our previous work by examining the effects of additional amines and subjecting bonded products to additional testing. Solid wood joints bonded with a variety (7 of 15) of modified adhesives had resistance to cyclic stress superior compared to that of joints bonded with unmodified urea–formaldehyde adhesive; at least three of the modified adhesives approached the behavior of phenol–formaldehyde-bonded joints. Resistance to moist heat aging, although still inferior to that of phenol–formaldehyde-bonded joints, was significantly improved for joints bonded with modified adhesives over joints made with unmodified resins. The fracture behavior of joints made with modified adhesives was different from that of joints made with unmodified resins. The fracture energy was greater for joints made with three of four modified adhesives than for joints made with unmodified resins. Modified adhesives produced particleboards made with enhanced cyclic stress resistance. Formaldehyde emission from particleboards made with resins modified with urea-terminated amines was less than emission from boards made with unmodified resins. However, emissions from particleboards made with amine hydrochlorides were not improved compared to those from boards made with an ammonium chloride curing agent. © 1993 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Effect of fiber-matrix adhesion on the properties of short fiber reinforced ABS

The tensile strength, fracture energy, and impact strength of ABS reinforced with discontinuous crystalline fibers such as Fybex

1 Du Pont trademark.

can be controlled by manipulating fiber-matrix interfacial adhesion. In “good bonding” situations composite tensile strength, thermal expansion coefficient, and elastic moduli are significantly improved over the unfilled resin. The excellent impact strength of unreinforced ABS can be retained by lowering the fiber-matrix interfacial adhesion. This results in a corresponding reduction in the improvements in tensile and flexural strength. However, the elastic moduli and thermal expansion coefficients are relatively insensitive to changes in adhesion. Consequently, a material with high modulus (>500,000 psi), high Izod impact resistance (7.0 ft-lb/in.), and low expansion coefficient (3.0 × 10^?5 in./in./°F) can be obtained. A material with this unique combination of properties should find use in large parts such as camper tops, truck grilles, and snowmobile bodies. Fiber-matrix adhesion was measured directly by an x-ray analysis technique which could be employed because of the fiber's crystallinity and unique growth habit. This independent measurement allowed a correlation between bonding and composite properties. The interfacial bond strength was manipulated by a variety of fiber coatings and resin additions.     

The hierarchical structure and flexure behavior of woven carbon fiber epoxy composite

The hierarchical structure and flexure behavior of woven carbon fibers epoxy composite were investigated in this work. First, the hierarchical structure of the composite is characterized on three levels: composite, ply, and yarn. Structura imperfections,

1 In this paper, “structural imperfections” is used to describe the inherent structural characteristics of the actual composite, which deviate from the theoretically ideal and perfect composites, control, that are used in composite theories.

such as, ply‐ply misalignment, ply‐ply offset, and resin pockets, are identified and described. Second, a four‐point bending arrangement is used to study the flexure properties of the composite. Additionally, in‐situ traveling microscope and acoustic emission (AE) techniques are utilized to gain insight to the failure proceses during flexure test. AE showed early stages of matrix cracking before visual observation, which makes it a valuable tool for early failure detection.     

New thermosetting resins for high performance composites

Investigations leading to the development of a new family of heat-stable thermosets, the Xylok

1 Registered trademark.

resins, are outlined. These polymers are the condensation products of aralkyl ethers or halides with phenols, and in some instances other classes of aromatic, heterocyclic and organometallic compounds, in the presence of a Friedel-Crafts catalyst. They are fast curing and Xylok composites have been prepared with glass, asbestos and carbon fibre reinforcement, which give excellent high-temperature mechanical strength and strength retention on prolonged exposure up to 250°. A comparative evaluation of the mechanical and electrical properties of a series of glasscloth laminates prepared with various classes of thermosetting resins has shown the Xylok resins to give outstanding overall performance. In addition, the chemical and radiation resistance, and ablative, wear and frictional properties of the Xylok composites suggest that they will find use in chemical plant, aircraft aerospace and bearing applications. Asbestos flour-filled Xylok moulding compounds have been shown to give similar flow and curing characteristics to phenolic based products, but the mouldings are significantly more heat stable.     

Viscoelastic melt behavior of poly(2,6-dimethyl-1,4-phenylene oxide), high-impact polystyrene,and a 35–65 blend

The viscoelastic melt behavior of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO

1 PPO is a registered trademark of the General Electric Company.

resin), high-impact polystyrene (HIPS), and a 35–65 blend of these polymers has been characterized by measuring the steady shear viscosity and primary normal stress difference and the dynamic storage and loss moduli as functions of shear rate or frequency and temperature. Time–temperature superpositioning was used to generate master curves of each type of data for a reference temperature of 260°C. This procedure required five different empirical shift factors for each material. These shift factors show large differences between PPO resin and HIPS and exhibited large deviations from the WLF equation with universal constants. This result suggests that the temperature dependence of the relaxation processes in PPO resin is significantly different from the temperature dependence of HIPS relaxations. Flow activation energies computed from the viscosity data for PPO resin are much higher and more shear sensitive than those calculated for HIPS. The computed relaxation spectra clearly display the effect of long-time relaxation mechanisms associated with PPO molecules when compared to HIPS. The 35–65 blend exhibits general rheological compatibility with material parameters and responses intermediate between PPO resin and HIPS. This result is indicative of a high degree of segmental mixing for the two components in the blend.     

Difurfuryl diisocyanates: New adhesives derived from renewable resources

The syntheses of difurfuryl diisocyanates [e.g., ethylidenebis (2,5-furandiylmethylene) diisocyanate (EDFI)] have been reported in the literature. Difurfuryl diisocyanates are structurally similar to diphenylmethane diisocyanate (MDI), which has proven to be an excellent adhesive for bonding wood composites. The MDI regin is synthesized from petroleum-derived chemicals; the EDFI resin is synthesized from biomass-derived chemicals. In this study, the mechanical properties of aspen flakeboards bonded with MDI and EDFI are compared. In general, results show that the strength properties of flakeboards bonded with MDI are only marginally better than those bonded with EDFI. Because EDFI is more viscous than is MDI less than optimum atomization of the EDFI resin during spraying of the flakes is believed to be largely responsible for the differences in strength property values. The dry internal bond strength values of flakeboards bonded with MDI (1.33 MPa; 193 lb/in.²) at 3% resin content are significantly greater than the 0.41 MPa (60 lb/in.²) required by the American National Standards Institute (ANSI/A208.1) for type-2 medium-density particleboard. © 1993 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Temperature gradients in the channels of a single‐screw extruder

We used a temperature‐sensitive fluorescent dye, perylene, to monitor the true resin temperature during extrusion of polycarbonate. The measurement involved doping polycarbonate with perylene and detecting fluorescence with an optical sensor that accesses a standard instrumentation port on a barrel of a single‐screw extruder. The sensor's confocal optics design permits fluorescence intensity measurements as a function of position. Using a previously established calibration function, temperature and temperature gradients were obtained from the measured fluorescence. Because the origin of the measurement is the fluorescent dye molecule that is soluble in the resin, this method allows temperature measurement of the polymer without interference from the surrounding metal parts. With the sensor looking over the screw, temperature profiles from the barrel wall to the core of the screw were obtained as a function of screw speed, screw design and resin melt flow rate. Polym. Eng. Sci. 44:2148–2157, 2004. © 2004 Society of Plastics Engineers.

1 This paper is a contribution from the National Institute of Standards and Technology, and, thus, is not subject to copyright in the United States.

     

Synthesis and characterization of melt-polymerizable aminophthalocyanine monomers

The strategy, synthesis, and characterization of a soluble amine-functionalized phthalocyanine monomer and two examples of its polymerization into optically transparent glasses are reported. A simple, fast, and versatile method for incorporating metal ions into the metal-free phthalocyanine is demonstrated. Measurements of the nonlinear optical properties associated with a lead-substituted phthalocyanine/urethane copolymer are also reported. © 1995 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Fracture behavior of coated/uncoated graphite-epoxy composites

The static delamination behavior of graphite/epoxy composite specimens subjected to mode I tensile opening (using UDCB

1 Uniform double cantilever beam.

specimens), and pure mode II shear loading (using ENF

2 End-notched flexural.

specimens) were studied. The graphite epoxy composites for the study were made from commercially treated fibers, with and without an electropolymerized interlayer. The mode I fracture energy (G_IC) was found to be significantly higher (more than 50 percent) for the coated fibers. However, this improvement was accompanied by a high reduction (more than 3 times) in the mode II fracture energy (G_IIC). This effect is apparently related to poor adhesion between the interlayer and the epoxy resin, which may be corrected by use of a “top layer” of appropriate composition to form chemical bonds between the phases. The fracture toughness (K_IC) of composites made with commercially treated fibers was also evaluated, using double side-notched specimens.     

The synthesis and properties of a cation-exchange resin prepared by the pyrolysis of starch in the presence of phytic acid

A black charcoal-like material having cation exchange and adsorption properties was prepared by the controlled pyrolysis of starch in the presence of a commercial phytic acid solution. Resins with binding capacities of 0.7–5.7 meq/g of calcium were prepared by varying the phytic acid to starch ratio, the temperature, or the duration of heating of the reaction mixture. SEM photomicrographs of some of these new materials showed that they are composed of particles similar in size and shape to the starting starch granules. These resins also removed atrazine from aqueous solutions. © 1995 John Wiley & Sons, Inc.

1 This article is a US Government work and , as such, is in the public domain in the United States of America.

     

Styrene emulsion polymerization in the presence of a maleate-functional surfactant

Dodecylhemiester of maleic anhydride is a very good anionic stabilizer for the emulsion polymerization of styrene. Rather high solid contents may be produced. Up to about 70% of the surfactant can be grafted onto the surface of the particles. Upon floculation with calcium salt, only 3% of the surfactant is left in the washing water. © 1997 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

J Appl Polym Sci 65: 2289–2296, 1997     

Behavior of amine-modified urea–formaldehyde-bonded wood joints at low formaldehyde/urea molar ratios

Urea–formaldehyde-bonded wood products are limited to interior nonstructural applications because of their poor durability under cyclic moisture or humid environments. The stability of solid-wood joints and particleboards can be enhanced by bonding with urea–formaldehyde adhesives modified with di- and trifunctional amines at an effective resin formaldehyde-to-urea mol ratio (F/U) of 1.6; however, particleboard formaldehyde emissions were not improved over those from boards made with unmodified adhesives and were unacceptably high. The relative effectiveness of selected modifications was investigated at resin form aldehyde-to-urea (F/U) molar ratios of 1.4 and 1.2 Solid-wood joints and particleboards made with modified adhesives, an unmodified adhesive, and a phenol formaldehyde (PF) resin were subjected to cyclic soak-dry (cyclic stress) treatments and moist-heat aging. Formaldehyde emissions from particleboards were also determined. At F/U 1.4, the resistance of solid-wood joints made with modified adhesives to cyclic stress and moist-heat aging was equal to that of PF-bonded joints and superior to that of joints bonded with unmodified adhesive. The resistance of particleboards made with modified adhesives was greater than that of boards made with unmodified adhesive but less than that of PF-bonded board. Solid-wood joints and particleboards made with F/U 1.4 resins performed better than did those made with F/U 1.2 resins. Particleboards made with F/U 1.2 resins had formaldehyde emissions well below the standard, and room temperature aging or bonding at high temperature reduced emissions substantially. © 1994 John Wiley & Sons, Inc. 1

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Solvent replacement in the synthesis of persubstituted phosphonitrilic hydroquinone prepolymer materials

A desirable solvent replacement has been effected in the synthesis of persubstituted phosphonitrilic hydroquinone prepolymer materials. The replacement of carbon tetrachloride with cyclohexane has no adverse effect on the composition and quality of the material prepared. The overall yield of the reaction increases from 65 to 70% and the toxicity of the reaction mixture and of the waste generated from the reaction are greatly reduced. The particularly close match of solvent properties between carbon tetrachloride and cyclohexane makes this an excellent solvent replacement. Such changes to less-expensive, less-toxic, and less-environmentally damaging solvents are on the increase. A brief list of some known replacement solvents for use in polymer and coatings applications is presented. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Alumina trihydrate as a flame retardant filler for flexible vinyl compounds

In those flexible vinyl compounds which can accept fillers, alumina trihydrate can significantly improve flame resistance as measured by oxygen index

1 It should be appreciated that degrees of flammability as measured by small-scale tests such as oxygen index may in no way reflect the relative hazard of these same materials when involved in a fully developed fire.

. Over a range of plasticizer concentrations, the lower the concentration of burnable plasticizer, the greater the contribution of hydrate to flame retardancy. Combinations of alumina trihydrate with antimony oxide are especially effective for improving the flame resistance of flexible vinyl compounds.