Hoffman Weeks

Table 20.3 Results obtained for the equilibrium melting temperatures from the Hoffman-Weeks plots of the P(HB60-ET40)/ PET and P(HB80-ET20)/PET blends...

The lamellar habit adopted by crystalline polymers adds surface terms to the specific Gibbs function (chemical potential), most importantly the fold surface free energy, ae, which contributes 2ae/Xg for a lamella of thickness k and crystalline density q. In consequence melting points are lowered from T, for infinite thickness, to Tm according to the Hoffman-Weeks equation... 

Die Keimbildungsarbeit AG in Gl. (15) wird bei Hochpolymeren unter Annahme eines zylinderformigen Keimes (vgl. S. 614) berechnet. Man setzt fur diesen gewohnlich an [Mandelkern, Quinn und Flory (191, 192, 195), Hoffman, Weeks und Murphey (117), Kahle und Stuart (143, 144)]... 

Wie Hoffman, Weeks und Murphey (117) richtig ausgefiihrt haben, gelten aber diese Gleichungen nur fiir Kristallisationstemperaturen, die... 

A good straight line results when T of the L peak is plotted against Tc for i-PS materials crystallized between 150 - 180 C, see Figure 3. Extrapolation of this line to the T = Tc line, suggested by Hoffman-Weeks... 

Figure 3. Hoffman-Weeks construction for i-PS crystallized between 150 and 180 C.

Figure 6. Hoffman-Weeks constructions for i-PS crystallized from blends with 20%PEC.

The equilibrium temperature of a polymer (blend) can experimentally be determined by a Hoffman-Weeks plot, which is a plot of the experimental melting point versus the crystallization temperature T vs. T) as presented in Figure 3.18. Extrapolation from experimental data to the r =T line results in the value of T... 

Figure 3.18. Hoffman-Weeks plot for PCL rich PCL/PC blends (the data are displaced by 5°C to discern the different blend compositions) [Jonza and Porter, 1986],...

Hoffman-Weeks plots have also been drawn for several other amorphous/crystalhne miscible blends, such as PVDF/PEMA [Eshuis et al., 1982], PEG/PMMA [Martuscelh, 1984], PCL/SARAN [Zhang and Prud homme, 1987], as well as for some miscible blends containing two semicrystalline components, PCL/PC [Jonza and Porter, 1986] and PCL/Penton [Guo, 1990]. Table 3.10 represents equilibrium melting points derived from... 

Figure 3.19. Hoffman-Weeks plot for PVDF/PMMA blends with 50.1 vol. % of PVDF [Stein et al., 1981].

Table 3.10. Equilibrium melting points derived from Hoffman-Weeks plots for several crystallizable miscible blends...

A plot of the observed melting point of both melting endotherms as function of the crystallization temperature (Hoffman-Weeks plot) is another method to detect whether recrystalhzation occurs. The melting point of recrystallized material is independent of T thus a horizontal line is observed in the T vs. T plot. 

HIPS/PPS HIPS/SBS Historical notes Hodge model Hoffman-Weeks plot Homogenization... 

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