Authors:P. Atkinson, P. Haines, G. Skinner, and T. Lever
The use of thermal methods in the study of flammability and fire retardant action is discussed and compared with the standard test methods. This paper provides an overview with examples drawn from continuing studies on polyester resins, especially those containing halogenated monomers. Thermal analysis and cone calorimetry results are complemented byanalysis of the gaseous and solid products using a wide range of analytical methods.
Thermal analysis (TA) is useful for studying the
reaction and thermal properties of free radical cured photopolymers. Starting
with reactive liquid monomers, the photocuring reactions are initiated by
the interaction of UV radiation with an added photoinitiator to form free
radicals. The monomers generally are acrylates or methacrylates. Some of the
important characteristics of these systems that can be illustrated by TA methods
are: 1) the polymers are heterogeneous with more than one phase present even
when only one monomer is involved; 2) because of this heterogeneity they have
unusually broad glass transitions; 3) the degree of conversion achieved in
many UV cured systems is in the 60–80% range, so that considerable residual
monomer is often present; 4) partially cured, vitrified samples contain trapped
free radicals that will continue to react slowly; 5) when a partially cured
photopolymer is heated above its current Tg
a reaction exotherm is evident.
Some other aspects of photocuring
are not easily disclosed by thermal analysis. Studying fast photoreactions
by DSC may not give valid kinetic data because the reaction occurs faster
than the DSC instrument time constant. Optical methods (IR, Raman) can be
used to advantage in such cases. While photocuring resins are usually exposed
to light at ambient temperatures, the local temperature in the resin will
be quite elevated, resulting in Tg
values that are much higher than ambient. This has been demonstrated by thermal
modeling of the reaction and verified by infrared thermography.
Authors:P. Tabaddor, C. Aloisio, H. Bair, C. Plagianis, and C. Taylor
DSC, TGA and DMA thermal analysis techniques are used to characterize a complex adhesive blend. The chemical and thermomechanical property development shown to follow a two-stage process. Beneficial synergy between these analysis tools is demonstrated in this study.
Authors:G. Van Assche, A. Van Hemelrijck, and B. Van Mele
The influence of temperature modulation and signal treatment (deconvolution procedure) of modulated temperature differential
scanning calorimetry is discussed with respect to the investigation of cure kinetics of thermosetting systems. The use of
a ‘dynamic’ heat capacity calibration is not important for this purpose due to normalization of the heat capacity signal in
all cure experiments. The heat flow phase during isothermal and non-isothermal cure is always small, giving rise to negligible
corrections on the heat capacity and reversing heat flow signals in-phase with the modulated heating rate. The evolution of
the heat flow phase contains information on relaxation phenomena in the course of the chemical reactions.
Modulated temperature differential scanning calorimetry (MTDSC) is used to study simultaneously the evolution of heat flow
and heat capacity for the isothermal and non-isothermal cure of an epoxy-anhydride thermosetting system. Modelling of the
(heat flow related) chemical kinetics and the (heat capacity related) mobility factor contributes to a quantitative construction
of Temperature-Time-Transformation (TTT) and Continuous-Heating-Transformation (CHT) diagrams for the thermosetting system.
Differential scanning calorimetry (DSC) and thermogravimetry (TG) were used to examine the thermal behavior of the multimonomer
poly[2-(10-undecenoyloxy)ethyl methacrylate] (PUDEM) within the temperature range from -80 to 400C. DSC measurements indicated
that the polymer side chains were able to crystallize in paraffinic phase. PUDEM, added to methyl methacrylate (MM), can effectively
copolymerize with essentially no homopolymer produced as shown by DSC (single Tg). The value of Tg depends on the PUDEM content, degree of cross-linking and the presence of free MM in the cross-linked product.
Authors:J. L. Martín, J. M. Salla, A. Cadenato, and X. Ramis
It is known that experimental parameters may affect peak characteristics in DSC studies. Kinetic parameters calculated from isothermal and dynamic runs, can also be affected by the choice of experimental conditions.
Authors:J. López, M. Rico, B. Montero, J. Díez, and Carmen Ramírez
The effect of thermoplastic modification of an epoxy-amine system on the cure reaction, miscibility and thermal stability
of the system was investigated. The cure kinetics showed an autocatalytic behavior. Modifier did not affect either the total
reaction heat or the achieved maximum conversion but delayed the kinetics. The model of Horie-Kamal corrected by diffusion
factor was used to adjust kinetics in the whole range of conversions. The modified systems showed two glass transitions indicating
two separated phases, whose compositions were estimated using the Fox and Couchman equations. Modifier did not affect the
thermal and thermooxidative stability of the system.
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.