With the help of the c-DTA® calculated DTA signal, endothermal and exothermal effects can be identified. In the following graph, the 2-step decomposition of a polyamide (PA) sample in a nitrogen atmosphere is presented. The melting peak, determined by c-DTA® to be at 226°C, identifies the sample as PA6. (measurement with TG 209 F1 Libra®)
It should be kept in mind when processing this material that the first mass loss step occurs already during melting; this is apparently the release of processing additives.
This composite material is composed of a matrix of pure carbon to which carbon fibers are added. It exhibits high mechanical strength associated with high temperature stability. Originally used in aerospace engineering, it is nowadays also applied in furnace and equipment manufacturing, hollow glass or the semiconductor industry.
The thermal expansion of C/C materials depend on their fiber architecture. In the present case, experiments with angles of 45° (black) and 90° (red) relative to the fiber orientation were conducted. Both curves depict a characteristic behavior of such fiber-reinforced composites: passing a length change minimum between approx. 300°C and 400°C followed by expansion.
At 2000°C, the relative length change (dL/L0 in %) as well as the corresponding mean CTE of the specimen cut out with a 45° angle relative to the fiber direction (black) are just about 7% higher (0.155% and 0.781 x 10-6 1/K) than that of the sample cut out with a 90° angle (red, 0.144% and 0.727 x 10-6 1/K). This suggests a quite low dependency of the material properties within these spatial directions.
With DEA, the curing behavior of reactive adhesives can also be measured directly during your process – i.e., in-situ. A large selection of sensors is available for tailoring your process to various temperature and pressure ranges.Curing is completed after 40 minutes as soon as a horizintal level of ion viscosity is achieved.
The most widely used encapsulant is EVA (ethylene vinyl acetate copolymer), due not only to its high electrical resistivity, low fusion and polymerization temperature, and low water absorption ratio, but also to appropriate optical transmission properties. As the polymerization reaction is irreversible, the thermal treatment of the PV cell encapsulation is crucial.
The quality and lifetime of the PV modules/arrays depend on the caliber of this production process.In this example, Dielectric Analysis of an EVA sample was carried out in the lab furnace of the DEA. The DEA system is optimally designed for materials with standard to long curing times (> 3 min).Time and temperature ramps can be easily programmed at heating rates of up to 40 K/min. In addition, all disposable comb sensors can be used in the furnace to ensure a broad application range of the system setup.
The multi-frequency measurement (with frequencies between 1 Hz and 10000 Hz) was carried out, and the ion viscosity (Ω.cm) was monitored. Presented here is the behavior of the ion viscosity at 1 Hz.The cross-linking reaction by using peroxide was observed under isothermal conditions at 150°C.The increase in the ion viscosity correlates with the increase in the degree of cure. After 60 min, the ion viscosity remains nearly constant, which indicates that the cross-linking reaction has essentially finished.
In this example, the curing of a carbon fiber-reinforced epoxy prepreg (CFRP) in a press at 120°C was measured at a frequency of 10 Hz. The plot shows ion viscosity (green curve) which is derived from the loss factor (blue curve). Ion viscosity increases as curing progresses and achieves a nearly horizontal level after 14 min, signaling a 100% degree of curing. The temperature measured on the same DEA channel yields a large exothermal curing effect: peak of 162°C.
Analysis and optimization of thermosets can easily be carried out using differential scanning calorimetry. Presented here is the DSC 3500 Sirius measurement on an epoxy resin. The exothermic peak detected at 135.5°C (peak temperature) during the 1st heating is caused by curing of the sample. After this first heating up to 200°C, the epoxy resin is completely cured. The glass transition of the cured sample can be determined by means of a second heating: it was detected at 115.0°C (midpoint).
The 3-D plot shows a TGA-FT-IR measurement on an EVA sample between 25°C and 600°C. The mass-loss steps of the EVA sample (TGA, black curve) correlate well with the absorption intensities between 650 cm-1 and 4000 cm-1. The evolved gases as 2-dimensional spectra can be extracted at any desired temperature and subjected to a library search (e.g., NIST-EPA library for evolved gases) for identification.
The lower plot shows the TGA (black), DTGA (black dashed) and the Gram-Schmidt graph (blue). The two additional extracted traces (temperature-dependent intensities; red and green curves) are in very good correlation with the DTGA curve. The 1st mass-loss step at 350°C is due to the release of acetic acid (red curve). In the 2nd mass-loss step, acetic acid has already been totally released. The green curve represents the absorption intensities of the released hydrocarbons resulting from the decomposition of the polymer backbone (DTGA peak at 468°C).
OIT tests (Oxidative-induction time) are well-known for evaluating the oxidative resistance of polymers, in particular polyolefins.
In this example, two PP samples were heated to 200°C under a dynamic nitrogen atmosphere. The endothermic peak detected during heating illustrates the melting of the polypropylene. After 3 minutes at 200°C, the gas was switched to air.
The resulting exothermic effect indicates the polymer degradation. In the present case, oxidation occurs earlier for sample A than for sample B (OIT 6.6 min vs. 11.6 min).
The plot shows the DSC results for two seemingly identical granulate batches, specified as Polyamide 66, which were delivered at different times (2nd heating after controlled cooling at 20 K/min). The blue curve (old batch) shows the glass transition at 63°C (mid-point) and the melting peak at 263°C, which are both typical for PA66. The new batch (red curve), however, exhibits a double peak with peak temperatures at 206°C and 244°C. This indicates that the new granulate most probably contains a second polymer which blends with PA66.
Volatile components in paints are of environmental issue during application. Water-based paints and powder coatings reduce this problem to a great extent. 31.9 mg of a two component hydro clear coat were analyzed in the TG 209 F1 Libra® coupled to a VECTOR 22 FT-IR spectrometer. The sample was heated at a rate of 5 K/min in a nitrogen flow of 45 ml/min up to 300°C. The main weight loss up to 100°C was clearly attributed to the water, but significant contributions come also from hydrocarbons, like alkyl acetates and aliphatic alcohols. The maximum evolution rate for these latter components is shown by the two peaks in the traces at 154°C. During drying of this clear coat, no indication of harmful or toxic volatiles was found.
The irradiation for 1 s of a sample of hexandiol diacrylate (HDDA) was investigated using three different atmospheres. The heat of cross-linking is at its highest under an inert atmospehre of 100% nitrogen (green curve) with 378 J/g. A mixture of 50% nitrogen and 50% oxygen yields 268 J/g (blue curve), a pure oxygen atmosphere only 170 J/g (red curve). There is obviously a competitive reaction due to the influence of oxygen. (measurement with Photo-DSC 204 F1 Phoenix®)
With a multi-frequency measurement, frequencies beyond the measurable range of the DMA can be achieved by using the superposition method. Employing the Williams-Landel-Ferry (WLF) equation, values such as E' and tanδ can be extrapolated to 100.000 Hz at a certain reference temperature (here -20°C). (measurment with DMA 242 E Artemis)
TG-DTG-TIC plot of non-vulcanized Natural Rubber (NR), 3.36 mg, N2, continuous injection of the evolved gases at 1-min intervals. A constant high temperature is maintained in the GC column to allow the gas mixture to pass quickly and separate into its main components. (measurement with TG-GC-MS)
At the onset of the NR decomposition (32 min., 346.3°C), the primary volatile products are isoprene C5H8 (peak 1 in TIC chromatogram) and 1-methyl-4-(1-methylethenyl)-cyclohexene C10H16 (peak 2).
This continuous GC-MS mode shows the gas evolution as a function of temperature and time and allows for the selection of individual mass numbers (m/z) for continuous plotting as a function of temperature (single ion monitoring, SIM).
The second stage of the NR decomposition (onset at 38 min., 406.2°C) is characterized by the evolution of products in addition to isoprene and substituted cyclohexene (as shown above). These can be identified as 5,5-dimethyl-1,3-cyclopentadiene (C7H10, 94 m/z), 1-methylene-2-vinylcyclopentane (C8H12, 108 m/z) and beta-humulene (C15H24, 204 m/z).
Presented here are the measurement results on an ethylene propylene rubber foam, measured with an HFM 436/3/1 E. Additionally shown are literature values for this material supplied by the customer. It can clearly be seen that the measurement results are in agreement with the corresponding literature data within 2.5%. Furthermore, it can be seen that the HFM 436/3, connected to an external chiller, can perform measurements even at temperatures of -20°C.
The molding of a polyimide/graphite prepreg in a production press was automated using the ion viscosity to initiate processing steps. Pressure was applied when the ion viscosity detected the viscosity minimum of the material, the critical time when the resin would flow properly but the excess volatiles would not be trapped. An additional critical point was employed to trigger de-mold when the part was sufficiently cured, thus reducing cycle times and increasing throughput. This is reflected in a much lower price for the molding. (measurement with DEA 288 Epsilon)
The LFA 447 NanoFlash® allows easy and fast temperature-dependent measurements of the thermal diffusivity. Additionally, the specific heat can be determined by employing a comparative method. A direct determination of the thermal conductivity is possible, if the bulk density of the material is known. This method was used for the thermophysical properties characterization of a polymer tape between room temperature and 90°C. The calibration standard for the specific heat determination was Pyroceram 9606. It can clearly be seen that both the thermal diffusivity and specific heat changed significantly versus temperature. The resulting thermal conductivity depicts nearly no temperature dependence.
In a standard measurement, the evaporation of a low-molecular plasticizer is overlapped by the decomposition of the elastomer components (red curves). The plasticizer begins separating earlier due to the lower boiling point resulting from the vacuum (black curves). The plasticizer content can hereby be determined much more precisely. (measurement with TG 209 F1 Libra®)
Besides the plasticizer portion (ca. 7%), the first elastomer components during the decomposition of a rubber compound are derived at 383°C (38%) and the second at 448°C (31%). The carbon black portion is calculated at 20% and the ash content at 4%. The position of the peak temperatures of the derived TGA curves (DTG) show that the compound is a carbon black-filled NR/SBR rubber blend. (measurement with TG 209 F1 Libra®)
Analysis and optimization of the curing process of epoxy resins can be easily carried out using differential scanning calorimetry. Presented here is a measurement on a glass fiber filled epoxy measured in the DSC 200 F3 Maia®. The two-step exothermal cross-linking reaction slightly above the glass transition (at 101.5°C) is clearly visible during the first heating of the sample. After a controlled cooling at 5 K/min, the sample was heated a second time. Only a weak glass transition is visible at a higher temperature (142.4°C) compared to the first heating cycle.
A comparison of DEA and rheometer data during the cure of an epoxy-graphite composite system shows that for the first 150 min the mechanical viscosity and ion viscosity curves nearly superimpose, demonstrating the clear correlation between the two properties. Early in the 175°C final hold, the epoxy resin goes through gelation and the mechanical viscosity can no longer be measured. The ion viscosity signal continues to follow the entire reaction, even as the material cures into a rigid glass. (measurement with DEA 288 Epsilon)
As temperature is ramped, the multi-frequency loss factor ε" shows a series of dipole relaxation peaks as the epoxy resin passes through its glass transition temperature. The loss factor then rises rapidly as the epoxy melts, reflecting the dramatically increasing ionic mobility in the resin. The ion viscosity curve is derived from the ionic mobility component of the loss factor and is a frequency independent parameter related to the viscosity of the polymer before gelation and to rigidity after gelation. The ion viscosity initially decreases reflecting the effect of increasing temperature on the dynamic viscosity, of the resin. The initiation of reaction, however, competes with the temperature effect by restricting mobility and results in a clearly defined viscosity rises, reflecting the increasing viscosity and cure state of the material. To illustrate the degree of cure, the dielectric cure index may be utilized. (measurement with DEA 288 Epsilon)
The combination of a 3-point bending sample holder and a modulated sample force allows the visco-elastic properties of a material to be determined. A PTFE bar was measured between -150°C and 150°C under (rectangular) modulated force (fixed static force of 0.2 N and three different dynamic forces). Based on the expansion data and the sample geometry, the storage modulus E´ can be calculated as a function of temperature. The three typical PTFE transformations are clearly visible at around -100°C (ß-transition), between 0°C and 50°C (crystal to condis-crystal transformation) and above 100°C (glass transition). (measurement with TMA 402 F1/F3 Hyperion®)
In dental applications, light-curing dental composites are used as restoratives (fillings) or veneering materials. The materials are generally composed of methacrylate systems such as bis-glycol-dimethacrylate (bis-GMA) or urethane dimethacrylate (UDMA). Additional monomers are used as diluent or to guarantee the cross-linking abilities of the resin. Inorganic fillers up to 80 weight percent improve the mechanical properties and reduce shrinkage during cross-linking. (measurement with Photo-DSC 204 F1 Phoenix®)
Polycarbonate (PC) is a popular polymer material used among other things, for electric tool casings. To optimize the production/molding process by finite element simulations, the thermophysical properties have to be known. The thermal diffusivity can be determined not only in the solid region but also at temperatures above the glass transition (> 140°C) if a molten material cell is employed in the LFA 457 MicroFlash®. Together with the specific heat (measured with a DSC) and density data, the thermal conductivity can be determined. The silght increase in the thermal conductivity versus temperature is typical for 100% amorphous materials. Furthermore, the glass transition is visible in the specific heat curve and in the thermal diffusivity result. In the thermal conductivity result, this second order transition cannot be seen.
Graphite materials are known to show a maximum thermal conductivity around room temperature, which can easily be analyzed using the low temperature version of the LFA 457 MicroFlash®. The physical explanation for this maximum is the high Debye temperature of this material (> 1000 K). The decrease in thermal diffusivity with increasing temperature dominates the temperature dependence of the thermal conductivity in the high temperature region. The specific heat decreases stronlgy at temperatures below room temperature and dominates the temperature dependence of the thermal conductivity there.
The extent to which the elastic properties of a seal remain intact after being subjected to a constant load of longer duration is very important. To test this, an elastomer seal was loaded with a force of 3 N and then relieved to 5 mN. Following a 40-hour load time, 21% compression was observed. After a 30-minute relief period, the compression had reversed by 16.2%; after 60 min, by 16.8%. The visco-elastic properties of the elastomer were such that the sample did not return to its original length even after 30 hours. (measurement with TMA 402 F1/F3 Hyperion®)
Orientation effects, stretch conditions and shrinkage are measured under load for films. In this example, the expansion and contraction behavior of a 40-μm thick polycarbonate film was tested under tensile load. The results varied considerably depending on the load. Under low amounts of force (5 mN), the film contracted at higher temperatures; however, it expanded if greater force (50 mN) was applied. (measurement with TMA 402 F1/F3 Hyperion®)
The UV curing of a photo-initiated epoxy resin adhesive by cationic polymerization is also affected by the set temperature. At a constant exposure time of 60s, the higher temperature of 70°C (red curves for DSC and temperature) causes higher reactivity of the resin system (faster curing) as well as a higher heat of reaction (390 J/g). It is particularly important to be familiar with this property when dealing with dual-curing resin systems, both thermal and light-curing. (measurement with Photo-DSC 204 F1 Phoenix®)
The ability to determine specific heat capacity for the most varied of materials is an important task for the DSC. A mean error of < 2% was attained on NIST Standard Reference Material 705a, a polystyrene with narrow molar mass distribution, by using a heating rate of 10 K/min and various analysis methods.
Polyethylene terephthalate (PET) is a semi-crystalline thermoplastic polymer with a relatively slow crystallization rate. In the DSC experiments, the various levels of amorphousness (Tg 75°C-85°C) and crystallinity (recrystallization 146°C, melting 242°C) are apparent. The samples were cooled from the melt in the DSC 204 F1 Phoenix® with the intracooler at different rates prior to the heating shown.
PE materials such as high-density polyethylene (HDPE) are often used for the production of packaging materials and films. Differential scanning calorimetry is often used to characterize the melting behavior of such materials, but the DSC 200 F3 Maia® can do even more. Due to its excellent low-temperature performance and outstanding sensitivity, the system also allows the detection of the glass transition (at –119.9°C). This extremely weak step in the DSC-curve is presented in the embedded picture in more detail.
The thermal behavior of an EPDM rubber mixture was measured between –125°C and 160°C at 10 K/min. The glass transition was detected at –52.5°C. The melting above the glass transition (peak temperature at 31.4°C) is typical for the behavior of a sequence-type EPDM. The further endothermal effects (at 98.6°C and 110°C) are due to the evaporation of processing agents. The presentation in the separate window clearly shows the high sensitivity of the DSC 200 F3 Maia® even for small energetic effects (0.43 J/g).