James A. Koutsky

Correlation between nodular morphology and fracture properties of cured epoxy resins

Various bulk epoxy resin formulations, based on diglycidyl ether of bisphenol A (DGEBA) and cured with diethylene triamine (DETA) were studied. Methods of linear elastic fracture mechanics were employed and all systems were characterized by the corresponding values of the critical strain energy release rate for crack initiation and crack arrest. Fracture morphology was studied by scanning electron microscopy and transmission electron microscopy of carbon—platinum surface replicas. An apparent correlation between morphology and ultimate mechanical properties has been found. All fracture surfaces are shown to be characterized by distinct nodular morphology. Nodules, ranging in size from 15–45 nm, represent the sites of higher crosslink density in an inhomogeneous network structure. Fracture surfaces were further characterized by three crack propagation zones. A smooth, brittle fracture zone was preceded and followed by crack initiation and crack arrest zones, respectively. An apparent plastic flow was confined to the initiation and arrest regions. No crazing phenomenon was seen in the initiation zone; instead a step-like fracture was observed, typified by the ‘flow’ of internodular matrix during step formation. Local plastic deformation in the initiation zone and the corresponding value of critical strain energy release rate, GIc, were correlated with the nodular morphology. The size of nodules was found to vary with the curing agent concentration, thus allowing us to establish a fundamental correlation between the nodular morphology and the ultimate mechanical properties of epoxy resins.

Formaldehyde Liberation and Cure Behavior of Urea-Formaldehyde Resins

On a etudie par calorimetrie differentielle a balayage le comportement au durcissement de plusieurs adhesifs uree-formaldehyde pour bois qui contenaient differents systemes de catalyseurs et agents neutralisants

The Interlaminar Fracture Energy of Glass Fiber Reinforced Polyester Composites

This study deals with the interlaminar fracture energy of a glass fiber reinforced polyester composite. Width tapered double cantilever beam (WTDCB) specimens are used for the test. The compliance and fracture behavior of the specimen as well as the effect of specimen geometry on fracture energy are studied. The fracture energy at liquid nitrogen temperature (77°K) is also studied. It is found that the fracture energy obtained decreases with increasing height of specimens, finally reaching a constant value. The minimum height requirement for the fracture test of Extren is one half inch. The fracture energy slightly decreases with a decrease in specimen taper. A load-deflection hysteresis is observed to increase with specimen width. Hysteresis is dependent on the beam volume, i.e., height, taper and crack length. The fracture energy at liquid nitrogen temperature (77°K) is about 3 times higher than that at room temperature and the fracture energy transverse to the fiber direction is slightly higher than in the fiber direction.

Etching of Polymeric Surfaces: A Review

Abstract The selective etching of polymeric surfaces has been of considerable interest to many polymer scientists and engineers. Some prime concerns of selective etching have been to increase the roughness of polymeric surfaces, change the surface chemical constitution, degrade or dissolve low molecular weights which migrate to the surface, and relieve residual surface stresses. Every polymeric surface, thermoplastic or thermoset, amorphous or crystalline, has, to some extent, different morphology from the bulk. Etching can considerably change the morphology and chemical properties of polymeric surfaces. An important commercial example is the etching of polymers prior to the subsequent metal plating [35, 74]. The adhesion and durability of the metal plate are greatly influenced by the condition of the polymeric surface. The increased surface area gives rise to a larger density of sites for the subsequent metal deposition. In many cases the chemical reactivity of etched surfaces is also increased upon etch...

A Morphological Study of Urea-Formaldehyde Resins

Abstract The solid state of a variety of urea-formaldehyde (UF) resins has been characterized by optical and scanning electron microscopy and wide angle x-ray diffraction studies. A first group of resins of various formaldehyde to urea mole ratios (F/U=1.0, 1.25, 1.5) and solids contents (25%, 45%, 65%) were prepared from oligomeric UF species and cured with NH4SO4 catalysts at room temperature for 120 days, and 90°C for 24 hours. Cured samples were dried by vacuum and elevated temperature (160°C). A second group of resins was also prepared by a more standard procedure to obtain F/U=1.2 and 1.6 and a solids content of 65%. These samples were cured at 160°C for 4 and 5 minutes with NH4C1 catalyst. The first group of samples showed colloidal character and definite crystallinity especially as F/U decreased to 1.0. The crystals appeared to have high melting points (Tm>230°C) and the formulation of the resin did not appear to vary the crystal structure but only the percent crystallinity. The water content of t...

Phase identification in calcia-alumina fibers crystallized from amorphous precursors

Amorphous fibers of a 46.5 wt% CaO-53.5 wt% Al2O3 eutectic compound were produced by inviscid melt-spinning. Fibers were subsequently heat treated at 900, 1000 and 1100°C for times ranging from 6 to 6000 s to elucidate crystallization processes. Fiber samples were ground for X-ray analysis. Equilibrium compounds Ca12Al14O33, Ca3Al10O18 and CaAl4O7 were present in varying amounts in all crystallized fibers. Liquid formation in fibers exposed to 1100°C for 6000 s was noted.

The effect of boria and titania addition on the crystallization and sintering behavior of Li2O-Al2O3-4SiO2 glass

Abstract Crystallization and sintering behaviors of four β-spodumene (Li 2 O-Al 2 O 3 -4SiO 2 ) glasses having different compositions were investigated and compared by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The Li 2 O-Al 2 O 3 -4SiO 2 glass containing both B 2 O 3 and TiO 2 showed the lowest activation energy value for crystallization (220 ± 8 kJ/mol), whereas the stoichiometric Li 2 O-Al 2 O 3 -4SiO 2 glass showed the highest value (322 ± 4 kJ/mol). The crystallization peak temperature (T p ) decreased from 918 to 819°C by the addition of both B 2 O 3 and TiO 2 to the stoichiometric Li 2 O-Al 2 O 3 -4SiO 2 glass. The Li 2 O-Al 2 O 3 -4SiO 2 glass containing both B 2 O 3 and TiO 2 showed approximately the same degree of sintering as the Li 2 O-Al 2 O 3 -4SiO 2 glass containing only B 2 O 3 .

Wetting behaviour and mullite formation at the interface of inviscid melt-spun CaO-Al2O3 fibre-reinforced Al-Si alloy (4032) composite

Inviscid melt-spun calcia-alumina fibre-reinforced aluminium-silicon alloy (4032) composites were produced using a melt-infiltration technique. Scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to investigate interfacial wetting and interphase formation, and identify the crystalline phase of the interphase of these composites. The composites processed at 700°C showed a good interfacial wetting and silicon accumulation at the interface. The composites processed at 927°C showed formation of an interphase region of about 10–20 μm thick, as well as excellent interfacial wetting. EDS analysis gave averaged compositions of this interphase region at 74 wt % Al and 26 wt % Si, which corresponds to the composition of mullite (3Al2O3 · 2SiO2). The formation of mullite at the interface was confirmed by XRD analysis.

Cellulose/Polypropylene Composites: The Use of AKD and ASA Sizes as Compatibilizers

Abstract Alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA) were used in both solution and emulsion forms to treat 100% cellulose and 70/30 wt.% cellulose/polypropylene composite sheets made by both an air-formation technique and traditional wet handsheet formation. In all cases, the air-formed sheets had poorer mechanical properties than did the handsheets. While the treatments appeared to have a visible affect on the spreading of polypropylene over cellulose, the effects of the treatments on mechanical properties were almost always negative. Annealing the wet-formed handsheets for five minutes at 130°C before pressing gave control sheets with improved modulus, strain-to-break, and burst strength, but had a slight negative effect on air-formed sheet properties. The effect of treatments on the water durability of the air-formed sheets was minimal or adverse, while for the wet-laid handsheets, the treatments were slightly beneficial if the sheets had been annealed, but detrimental if they had not.

Phenol-Formaldehyde Resin Curing and Bonding in Steam-Injection Pressing Part II. Differences Between Rates of Chemical and Mechanical Responses to Resin Cure

Summary Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) were applied to samples of phenol-formoldehyde resole resins that had been previously exposed to dry precure conditions. The area under tan delta curves during DMA isothermal scans of such samples decreased as the degree of precure increased; this area was used as an empirical measure of the rate of mechanical cure for phenolic resins. Similarly, the DSC exotherm area decreased with greater sample precure; this area was used to measure the rate of chemical cure. Rates of mechanical and chemical cure differed for different resins and with temperature. Under dry precure conditions at 115° and 140°C, a high degree of mechanical cure was achieved at a low degree of chemical cure.