Spherulites equilibrium melting

Only minor effects were found on the equilibrium melting temperature and degree of crystallinity. Polarized optical microscopy observations revealed that the spherulites size decrease and the number increase with attapulgite content (Figure 12.14). 

The experimental melting point of a-spherulites crystallized under usual thermal condition is 165°C. Literature data for the equilibrium melting temperature of a-iPP (T (a)) are very contradictory. The reported values faU into the range 174-220°C [1], the author accepts T (a)) = 208°C as the most reliable one [2]. 

Kressler et al. [106] also determined the melting behaviour of the spherulites. They determined the variation in T with T<- and found very large melting point depressions extrapolation of T s of samples crystallised at different T -S to T = T(. led to an equilibrium melting temperature of about 85 °C which is far greater than the usually accepted value of 71.5 °C observed melting points were nonlinear with Tj. and varied with time of crystallisation, indicating some complexity in the system. 

The radial growth rates of polymeric spherulites are expressed as a function of undercooling from their equilibrium melting point according to the well-known equation of Hoffman and Lauritzen [4,5],... 

Fig. 9.59 Plot of temperature of maximum spherulite growth rate, Tmax, against equilibrium melting temperature. I m, for indicated polymers. (1) isotactic poly(styrene) (a) (2) poly(tetramethyl-p-silphenylene siloxane) (b) (3) poly(cis-isoprene) (c) (4) poly(caproamide) (d,e) (5) poly(L-lactic acid) (f) (6) poly(phenylene sulfide) (g,h) (7) poly(R-epichlorohydrin), poly(S-epichlorohydrin), poly(I-RS-epichlorohydrin) (i) (8) poly(ethylene terephthalate) (j,k,l) (9) poly(aryl ether ether ketone) (m,n) (10) poly(ethylene-2,6-naphthalene dicarboxylate) (n) (11) poly(3-hydroxybutyrate) (o) (12) isotactic poly(methyl methacrylate) (q) (13) poly(dioxolane) (r) (14) New TPI poly(imide) (s) (15) poly(methylene oxide) (t) (16) poly(cis-butadiene) (u) (17) poly(propylene oxide) (v,w) (18) poly(imide) BPDA - - 134 APB (x) (19) poly(imide) BPDA - -C12 (x) (20) syndiotactic poly(propylene) (y) (21) poly(3-hydroxy valerate) (z) (22) poly(ethylene succinate) (aa) (23) poly(aryl ether ketone ketone) (bb) (24) poly(phenylene ether ether sulfide) (cc) (25) poly(tetramethylene isophtha-late) (dd) (26) poly(hexamethylene adipamide) (e,ee) (27) poly(tetrachloro-bis-phenol-A adipate) (fQ nylon 6-10 (ee).

The dependence of the spherulite growth rate on copolymer composition can be calculated from first principles. For illustrative purposes, a coherent unimolec-ular type nucleation is assumed. The spherulite growth rate in the vicinity of the equilibrium melting temperature can then be written as... 

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