Origin of Transcrystallinity and Nucleation Kinetics in Polybutene-1/Fiber Composites

Abstract

This work presents an in-depth study of fiber-induced nucleation and crystalline morphology in polybutene-1/single-fiber composites. The nucleation ability of various fibers, including carbon, glass, polypropylene (PP), poly­(l-lactide) (PLLA), and stereocomplex (SC)-poly­(lactide), is investigated via polarized optical microscopy. A polybutene-1 (PB-1) fiber made of the trigonal Form I polymorph is also adopted in an all-PB-1 composite. Two different types of morphologies of PB-1 Form II developed on the surface of the different fibers during isothermal crystallization. They are a transcrystalline layer (TCL) on the Form I fiber only and a hybrid shish–calabash (HSC) on all of the other fibers. Upon nonisothermal crystallization, a transition from the HSC to TCL morphology for the sole PP fiber is found. Quantitative studies of nucleation kinetics showed that the lowest nucleation free-energy barrier is exhibited by the PB-1 Form I fiber, due to the occurrence of cross-nucleation with Form II, possibly via epitaxial matching. On the other hand, the highest nucleation energy barrier is that of the PP fiber, despite the very similar chemical constitution. Moreover, a large variation in the pre-exponential factor of the nucleation rate among the various fibers suggests major differences in the available nucleation sites per unit area. The number of such sites is found to inversely correlate with surface roughness and, for the first time, is used to understand the obtainable morphology. In fact, we show that, notwithstanding the height of the free-energy barrier for nucleation, TCL can only be obtained when a sufficiently high number of nucleation sites are provided.

Surface Nucleation of Dispersed Polyethylene Droplets in Immiscible Blends Revealed by Polypropylene Matrix Self-Nucleation

“…Ishida and Bussi showed a value of Δσ of 0.3 erg/cm 2 for PE nucleated on PE fiber, for which, besides the apparent chemical similarity, lattice matching was obviously verified. A similar value of Δσ was obtained by Wang et al for polybutene-1 Form II on polybutene-1 Form I fiber, and was tentatively attributed to epitaxial crystallization . In other investigations, values of Δσ below 1 erg/cm 2 were found in systems where crystallizing polymer and nucleating substrate were chemically different, but matching between the lattice parameters was possible. , …”

“…Furthermore, the low Table 3. Induction Time (t 0 ) and Parameters Optimized through Fitting the Data in Figure 8a with eq 4 (ΔH ∞ , τ c , n) 54 In other investigations, values of Δσ below 1 erg/cm 2 were found in systems where crystallizing polymer and nucleating substrate were chemically different, but matching between the lattice parameters was possible. 41,43 Noteworthy is the significant difference that was found between I 0 of the two data series.…”

“…Thus, a lower value of Δσ corresponds to a lower energy barrier for nucleation of a specific crystallizing polymer on the given substrate. 23,[41][42][43]54 On the other hand, I 0 depends upon molecular and transport properties of the nucleating material, and it represents a frequency of nucleation events per unit area (in the case of surface nucleation). 23,54,55 For the evaluation of the data by means of eq 5, the employed values for U*, T ∞ , σσ e , Δh f , and T m °are 6276 J/ mol, 56 160 K, 56 1380 erg 2 /cm 4 , 42 280 J/cm 3 , 42 and 416 K, 42 respectively.…”

“…23,[41][42][43]54 On the other hand, I 0 depends upon molecular and transport properties of the nucleating material, and it represents a frequency of nucleation events per unit area (in the case of surface nucleation). 23,54,55 For the evaluation of the data by means of eq 5, the employed values for U*, T ∞ , σσ e , Δh f , and T m °are 6276 J/ mol, 56 160 K, 56 1380 erg 2 /cm 4 , 42 280 J/cm 3 , 42 and 416 K, 42 respectively. The value of the nucleation rate at each crystallization temperature, I, is calculated from the slope of the linear fitting performed with the first-order kinetics model, divided by the apparent interfacial area, which was calculated from the volume-average diameter (see Table 2).…”

“…On the one hand, Δ σ corresponds to the difference in the system surface’s free energy achieved with the formation of the first crystalline layer onto a substrate, i.e., with the replacement of a substrate/melt interface with a substrate/crystal and a crystal/melt interface. Thus, a lower value of Δσ corresponds to a lower energy barrier for nucleation of a specific crystallizing polymer on the given substrate. ,− , On the other hand, I 0 depends upon molecular and transport properties of the nucleating material, and it represents a frequency of nucleation events per unit area (in the case of surface nucleation). ,, …”