The addition of suitable cross-linking agents with norbornene-based monomers has significant effects on the thermal properties
of the resulting polymers formed by olefin metathesis. Ethylidene norbornene (ENB) and endo-dicyclopentadiene (endo-DCPD) were mixed separately with various loadings of three different cross-linking agents and then polymerized with the addition
of Grubbs’ catalyst. The polymerization kinetics and resulting glass transition temperature (Tg) of the systems were evaluated by differential scanning calorimetry (DSC).
The addition of the first cross-linking agent, norbornadiene (CL-1), to both endo-DCPD and ENB resulted in decreasing glass transition temperatures with increasing concentrations. In contrast, the addition
of the other two cross-linking agents (CL-2 and CL-3), which were both custom synthesized bifunctional norbornyl systems,
to both endo-DCPD and ENB resulted in a monotonic increases in Tg with cross-linker concentration. By tailoring the loading of these custom cross-linking agents, the properties of these polymer
systems can be controlled for various applications, including self-healing composites.
The influence of pressure on the polycondensation reaction between novolac resin (N) present in commercially available moulding
compounds and hexamethylenetetramine (HMTA) was studied up to 80 bars under air and in an inert atmosphere. For a low HMTA
content (N/HMTA=98/2 mass ratio) high pressure enables the detection of two successive curing reactions. With increasing HMTA
content the peak due to the first curing reaction becomes less pronounced at high pressure, while the enthalpy of the second
increases. In an inert atmosphere both curing reactions are well observable even at ambient pressure and for lower HMTA content
take place at lower temperatures, as expected. For the sample with N/HMTA=98/2 the curing reaction was followed using TG-MS.
the inorganic cations—which are located between the layers—by alkylammonium cations, to render the clay organophilic [ 1 – 4 ] and therefore compatible with hydrophobic polymers including epoxy thermosets. The nanocomposite morphology may be
, vitrification time and glass transition of the partially and fully cured thermoset resulted to be affected by the pressure.
The use of a pressure cell attached to a suitable TMDSC instrument allows to perform modulated DSC
monomer and onset of curing of monomer. Higher the difference better is the ease in fabrication and processing of thermoset composite. No melting endotherm, due to melting of diamine impurity, was present in DSC scans of monomers indicating absence of such
well as reduced oxirane content. [ 30 ] The DSC scan of isothermally cured epoxy thermosets, and the exothermic transition was absent which revealed their complete curing.
Results of DSC scans of
This biomaterials overview for selecting polymers for medical devices focuses on polymer materials, properties and performance.
An improved understanding of thermoplastics and thermoset properties is accomplished by thermal analysis for device applications.
The medical applications and requirements as well as the oxidative and mechanical stability of currently used polymers in
devices are discussed. The tools used to aid the ranking of the thermoplastics and thermosets are differential scanning calorimetry
(DSC), thermogravimetry (TG), thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) as well as a number
of key ASTM polymer tests. This paper will spotlight the thermal and mechanical characterization of the bio-compatible polymers
e.g., olefins, nylon, polyacetals, polyvinyl chloride and polyesters.
Modulated differential scanning calorimetry (MDSC) and dielectric analysis (DEA) have been used to characterize the cure process
of the system diglycidyl ether of bisphenol A (DGEBA(n=0)/1,2 diaminocyclohexane (1,2 DCH). The trans isomer and a mixture cis/trans(30-70% respectively) of 1,2 DCH were used to find their different behaviour. The study allowed to check the influence of
the cisisomer on the thermoset curing process. Gelation times were obtained through the equation proposed by Johari and vitrification
times from the point of inflection of the complex calorific capacity modulus.
The correlation between structure/microstructure and thermomechanical properties has been investigated by the Thermally Stimulated Creep (TSC) technique in a high performance thermostable thermoset matrix composite. The high resolving power of this technique allows us to analyse the α retardation mode. The kinetics of molecular movements liberated at the glass transition has been investigated by the technique of fractional loading: the analysis of each elementary process gives the real compliance and the retardation time as a function of temperature. The values of the activation parameters show the existence of a compensation phenomenon which characterizes the microstructure. It also gives access to the loss compliance of the composite material as a function of temperature and frequency. The predictive calculation of loss compliance has been validated by the results obtained by dynamic mechanical analysis (DMA).
A new method for determining the degree of conversion of gelation (αgel) and gel time (tgel) at gel point using a single technology, DSC, is discussed in this work. Four kinds of thermoset resins are evaluated. It
is found that the mutation points of reduced reaction rate (Vr) vs. reaction conversion (α) curves, corresponding with the changes of reaction mechanism, represents the gelation of the
reaction. The α at the mutation point is defined as αgel. From isothermal DSC curves, the point at αgel is defined astgel. Traditional techniques (ASTM D3532 and DSC method) are also used to determine αgel andtgel in order to demonstrate this new method. We have found that the results obtained from this new method are very consistent
with the results obtained from traditional methods.