Tg-onset value

The Tg (onset) values for spray-dried and freeze-dried lactose are shown in Figure 44.2 with corresponding water contents. Tg decreased with increasing... 

Figure 1.2 illustrates, using the same sample, how the rate of cooling through Tg and storage at room temperature bring into evidence the presence of the enthalphy relaxation effect as a superposition on the heat flow curve shift. Figure 1.2 also shows the extent of the Tg(onset)-value differences due to the presence of these endothermic peaks. It will be clear that a standardised Tg-value determination procedure is necessary to obtain reproducible results ... 

The Tg-values reported in this book are measured according to this procedure. A series of Tg(onset)-value determinations on rubber samples (i.e. 100% amorphous samples, providing a good sample/sample holder contact) resulted in a Tg(onset)-value precision of 0.5°C and a repeatability of + 1°C for this method. The reproducibility of this method was determined as 4°C during a round robin test with seven samples, measured in twenty-three laboratories [5]. These values might increase,... 

The disadvantages of using the Tg(onset)-value as Tg-value are discussed by Richardson [2]. Determination of the Tg-value using the enthalpy/temperature curve results in a theoretically better defined Tg-value. Software to follow this procedure is commercially available at present. In the (european) industry, however, the Tg(onset)-value method is used almost exclusively because it is not only convenient, but also yields an indication for the maximum application temperature of a polymer. 

The slightly improved repeatability of the He- and Hf2-values in comparison with that of the Hfl-value might be caused by the improved thermal contact between sample and sample holder after the fusion process. Nakamura [5] reports a reproducibility of 3°C for the Tm/Tc determination. The difference between the repeatability and the reproducibility values of the Tm/Tc determinations is thus considerably higher than those found for the Tg(onset)-value determination. 

Oil is also often a component of the car tyre rubber compound. It is blended with the pure rubber forming the so-called oil-extended rubber phase. Usually an aromatic oil is used such an oil showed a Tg(onset)-value at 232K (-41°C). But also naphtenic oil with a Tg(onset)-value of 208 K (-65°C) is used. 

Three different polypropylene (PP) modifications can be distinguished the atactic, the syndiotactic and the isotactic modification. The atactic modification is an amorphous polymer with a Tg(onset)-value of -21°C. The syndiotactic modification, made with a stereospecific homogeneous metallocene catalyst, is a semi-crystalline polymer (crystallinity about 25 %wt.) with a Tm-value of about 133°C [10]. The isotactic modification, made with a stereospecific heterogeneous Ziegler Natta catalyst is also a semicrystalline polymer (crystallinity about 50 %wt.) with a Tm-value of about 160°C and contains nearly always 2 %wt. - 5 %wt. of atactic material. 

The small, but clearly detected, increase of the Tg(onset)-value with an increasing 1,4 trans-BR content, confirms that the Tg-value of 100 %wt. 1,4 trans-BR is higher than that of 100 %wt. 1,4 cis BR. Tg-values of 1,4 cis- and 1,4 trans-BR of respectively -109°C and -94°C, obtained by extrapolation, were reported in Chapter 1.2.2. An 1,4 trans-BR content of 54 %wt. was however the highest trans content value of the results used for that calculation. The extrapolated Tg-value of 1,4 trans-BR shifts from -94°C to -92°C when taking into account these high trans content data. The extrapolated Tg-values of 1,4 cis- and 1,2-BR of respectively -109°C and -16°C did not change significantly. 

The Tg-values of a series of samples containing atactic 3,4-IR, cis 1,4-IR and only a small amount (< 3 %wt.) of 1,2-IR were extrapolated to 100 %wt. 3,4-IR to estimate the Tg-value of this material. The measured DSC Tg(onset)-values are listed... 

PK co- and terpolymer Tg effects can be detected by DSC both on dry, non-aged virgin powder and on fused samples. The results of the DSC Tg(onset)-value determinations on (virgin) powder samples proved to scatter, however, considerably due to the too strong influence of the crystalline phase on the shape of the Cp/T curve. Thus, a real DSC Tg(onset)-value determination of PK co- and terpolymer samples is only possible on non-aged, dry and one time fused samples. The reproducibility of this DSC Tg(onset)-value determination proved to be + 3°C. The average DSC Tg(onset)-value of a series of PK co- and terpolymer samples proved to be 4°C. 

DSC measurements were used subsequently to measure the Tg (onset)-values of these systems (measured during the heating mode, scanning rate 20°C/minute) ... 

Subsequently, the three samples were stored in an oven at 250°C (in a nitrogen atmosphere). The weight loss of the samples and the increasing Tg(onset)-values were followed as a function of time. 

The Tg(onset)-values of the samples B and C did not further increase from the moment that the sample weights became constant. The following end-values were measured ... 

Figure 10.1 shows the relation between the Tg(onset)-values and the amount of residual MIBK for the samples B and C. Both systems arrive, after evaporation of the solvent phase, at equal Tg(onset)-values. Figure 10.1 shows, however, that these equal end-values are reached along different ways. 

The Tg(onset)-value of both in the presence of solvent cured systems is indeed lower than that of the solvent-free cured system. This difference of 6°C + 1°C was also measured for a second identical series of DGEBA/DDM samples prepared with bis(2-ethoxyethyl) ether (BEE, boiling temperature about 150°C) as solvent phase. 

Subsequently, about 15 milligramme of sample was used for a DSC Tg(onset)-value determination (heating rate 20°C/minute). This Tg-value determination was used to confirm the possible presence of a BR and a NR phase. 

The film sample investigated proved to be a semi-crystalline polymer system with a DSC Tg(onset)-value of 16°C. The DSC Tm(l)-value was 146°C with a Hf(l)-value of 18 J/g. The so-called processing-window of this polymer proved to be about 50°C, from 150°C to about 200°C. This bio-polymer proved to be (as usual) strongly moisture dependent. The equilibrium water saturation of the film in contact with water was 64 %wt., however visual detectable swellings effects were not noticed. 

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