Abstract
To fabricate thermoplastic polymers exhibiting improved ductility without the loss of strength, a novel multiple-step melting/irradiation (MUSMI) strategy was developed by taking poly(vinylidene fluoride)/triallyl isocyanate (PVDF/TAIC) as an example, in which alternate melting and irradiation were adopted and repeated for several times. The initial irradiation with a low dose produced some local crosslinked points (not 3-dimensional network). When the specimen was reheated above the melting temperature, they redistributed in the PVDF matrix, which is an efficient way to avoid the high crosslinking density at certain positions and the disappearance of thermoplastic properties. During the subsequent cooling process, the crosslinked domains in the thermoplastic polymer matrix is expected to play double roles in turning crystal structures for enhancing the ductility without reducing strength. On one hand, they can act as heterogeneous nucleation agents, resulting in higher nucleation density and smaller spherulites; on the other hand, the existence of crosslinked structures restricts the lamellar thickening, accounting for the thinner crystal lamellae. Both smaller spherulites and thinner lamellae contribute to better ductility. At the same time, these local crosslinked points enhance the connectivity of crystal structures (including lamellae and spherulites), which is beneficial to the improvement of strength. Based on the influence of local crosslinked points on the ductility and strength, thermoplastic PVDF with much higher elongation at break and comparable yielding stress (relative to the reference specimen upon strong irradiation only once) was prepared via MUSMI successfully.
Highlights
In the wide applications of various materials, mechanical performance plays an important role [1,2].Much attention has been paid to strength and ductility, which can be evaluated by the parameters of yielding stress and elongation at break, respectively
The results indicated that the mechanical performances were under the control of crosslinking density
It is necessary to assess the thermodynamic miscibility between poly(vinylidene fluoride) (PVDF) and Triallyl isocyanate (TAIC)
Summary
In the wide applications of various materials, mechanical performance plays an important role [1,2]. The resultant mechanical performance dominates its applications, e.g., 3D printing [11,12,13]; on the other hand, the properties of polymers exhibit obvious dependence on the aggregation structures This is very typical in crystallizable polymers, in which higher crystallinity and bigger spherulites determine the higher yield stress and lower rupture energy [14]. A multiple-step melting/irradiation (MUSMI) strategy (Figure 1A) was developed to prepare thermoplastic polymers with improved mechanical performances, by taking poly(vinylidene fluoride)/triallyl isocyanurate (i.e., PVDF/TAIC) as an example. This system has been widely investigated since PVDF and TAIC exhibit excellent miscibility [26,27,28,29].
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