Abstract:By means of DSC, DTA, TG and NMR it was established that the process of cure of epoxy resins induced by aqueous solutions of heteropolyacids consists of two stages, the first one being connected with a catalytic interaction between oligomer and water, and the second one with epoxy-hydroxyl etherification. Analysis of kinetic data shows that the first reaction is diffusion controlled, the second process can be described by pseudo-first order kinetics with activation energy about 40 kJ]M.
“…Dependencies of Arrhenius parameters upon conversion for the epoxy−amine cure: (−) present data, (▪) ref , and (○) ref . ln A α relates to the present data alone.…”
Section: Resultsmentioning
confidence: 73%
“…The resulting dependence of E α on α for the epoxy cure is presented in Figure which also shows two dependencies of a very close shape discovered 5,13 for the cure processes. 1 DSC curves for the cure at different heating rates: 1, 1.0; 2, 2.0; and 3, 5.0 °C min -1 . 2 Dependencies of Arrhenius parameters upon conversion for the epoxy−amine cure: (−) present data, (▪) ref , and (○) ref . ln A α relates to the present data alone.…”
Section: Resultsmentioning
confidence: 85%
“…Differential scanning calorimetry (DSC) which measures the heat flow from the reacting system is a very convenient tool to study the overall epoxy−amine cure. − It is especially useful when a detailed mechanism has been established by other methods such as FTIR, ,,,− HPLC, ,− ,, and NMR. ,,, In such a case, the kinetic analysis of DSC data helps to determine those steps which most profoundly contribute to the overall process. This allows for the reduction of intricate mechanisms to an effective kinetic scheme.…”
The isoconversional kinetic analysis has been applied to
nonisothermal DSC data on the
cure of an epoxynovolac resin. The process reveals a dependence of
the activation energy (E
α) on
conversion
(α). The shape of the dependence has been interpreted in the
terms of the reaction mechanisms. It has
been found that the model dα/dt =
(k
1 +
α
m
k
2)(1 −
α)
n
used for the kinetically controlled cure
gives rise
to the dependence of E
α on α similar to the
experimentally found one. To completely describe the
diffusion-controlled cure, the effect of both T and α on the change
in diffusivity has been taken into account. The
equation for the specific rate constant of diffusion,
k
D(T,α) =
D
o
exp(−E
D/RT +
Kα), has been induced.
Its use allows us to obtain a model dependence of
E
α on α closely matching the experimental
one. A
technique of predicting isothermal cure from the sole dependence of
E
α on α has been considered.
“…Dependencies of Arrhenius parameters upon conversion for the epoxy−amine cure: (−) present data, (▪) ref , and (○) ref . ln A α relates to the present data alone.…”
Section: Resultsmentioning
confidence: 73%
“…The resulting dependence of E α on α for the epoxy cure is presented in Figure which also shows two dependencies of a very close shape discovered 5,13 for the cure processes. 1 DSC curves for the cure at different heating rates: 1, 1.0; 2, 2.0; and 3, 5.0 °C min -1 . 2 Dependencies of Arrhenius parameters upon conversion for the epoxy−amine cure: (−) present data, (▪) ref , and (○) ref . ln A α relates to the present data alone.…”
Section: Resultsmentioning
confidence: 85%
“…Differential scanning calorimetry (DSC) which measures the heat flow from the reacting system is a very convenient tool to study the overall epoxy−amine cure. − It is especially useful when a detailed mechanism has been established by other methods such as FTIR, ,,,− HPLC, ,− ,, and NMR. ,,, In such a case, the kinetic analysis of DSC data helps to determine those steps which most profoundly contribute to the overall process. This allows for the reduction of intricate mechanisms to an effective kinetic scheme.…”
The isoconversional kinetic analysis has been applied to
nonisothermal DSC data on the
cure of an epoxynovolac resin. The process reveals a dependence of
the activation energy (E
α) on
conversion
(α). The shape of the dependence has been interpreted in the
terms of the reaction mechanisms. It has
been found that the model dα/dt =
(k
1 +
α
m
k
2)(1 −
α)
n
used for the kinetically controlled cure
gives rise
to the dependence of E
α on α similar to the
experimentally found one. To completely describe the
diffusion-controlled cure, the effect of both T and α on the change
in diffusivity has been taken into account. The
equation for the specific rate constant of diffusion,
k
D(T,α) =
D
o
exp(−E
D/RT +
Kα), has been induced.
Its use allows us to obtain a model dependence of
E
α on α closely matching the experimental
one. A
technique of predicting isothermal cure from the sole dependence of
E
α on α has been considered.
“…Furthermore, analogous dependencies have been established for the first step of decomposition of (NH4) [VO(O,),(NH3)] [33] and for curing epoxy resins [34]. In the latter example an important role of diffusion has been pointed out [34].…”
Section: Identifying the Kinetic Scheme Of The Processmentioning
“…The extent and nature of the intermolecular crosslinking will, therefore, be determined in part by the correct choice of curing agent. The differential scanning calorimeter (DSC), which measures the heat flow from the reacting systems, is a very convenient tool to study the cure reaction of epoxy–amine systems 2–13. The incorporation of transition metals and their derivatives in epoxy resin have been examined in recent years.…”
During endochondral bone formation, chondrocytes undergo terminal differentiation, during which the rate of proliferation decreases, cells become hypertrophic, and the extracellular matrix is altered by production of collagen X, as well as proteins required for matrix mineralization. This maturation process is responsible for most longitudinal bone growth, both during embryonic development and in postnatal long bone growth plates. Among the major signaling molecules implicated in regulation of this process are the positive regulators thyroid hormone (T3) and bone morphogenetic proteins (BMPs). Both T3 and BMPs are essential for endochondral bone formation and cannot compensate for each other, suggesting interaction of the two signaling pathways. We have analyzed the temporal and spatial expression patterns of numerous genes believed to play a role in chondrocyte maturation. Our results show that T3 stimulates collagen X gene expression in cultured chondrocytres with kinetics and magnitude similar to those observed in vivo. Stimulation of collagen X gene expression by T3 occurs only after a significant delay, implying that this hormone may act indirectly. We show further that T3 rapidly stimulates production of BMP 4, concomitant with a decrease in the BMP inhibitor Noggin, potentially resulting in a net increase in BMP signaling. Finally, inhibition of BMP signaling with exogenous Noggin prevents T3 stimulation of collagen X expression, indicating that BMP signaling is essential for this process. These data position thyroid hormone at the top of a T3/BMP cascade, potentially explaining why both pathways are essential for chondrocyte maturation. J. Cell. Physiol. 219: 595-605, 2009. (c) 2009 Wiley-Liss, Inc.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
