Abstract
In this work, hydroxyl-functionalized boron nitride nanosheet (OH-BNNS) was prepared and was blended with poly(l-lactide) (PLLA) to yield PLLA/OH-BNNS nanocomposites with excellent dispersion of OH-BNNS via the interaction of carbonyl in PLLA and hydroxyl in OH-BNNS. The effects of OH-BNNS on the crystallization and melting behaviors, isothermal crystallization kinetics, macroscopic crystal morphology and crystal structure of PLLA were studied by means of various techniques. The addition of OH-BNNS nanofillers can effectively accelerate the crystallization of PLLA and enhance the nucleation density, leading to a smaller spherulite size, increased crystallinity, a more obvious crystallization peak upon cooling but weakened cold crystallization behavior upon heating. Low OH-BNNS loading can increase the relative content of α-crystal, but the relative content of less perfect αâČ-crystal is increased at high OH-BNNS loading due to the strong interaction between PLLA and OH-BNNS.
Highlights
Boron nitride is a crystal composed of nitrogen atoms and boron atoms and contains four different variants, hexagonal boron nitride (h-BN), rhombohtic boron nitride (r-BN), cubic boron nitride (c-BN) and wurtzite boron nitride (w-BN), in which h-BN is very similar to graphite in structure, and commonly known as white graphite due to its own whiteness [1]
The hydroxyl group of OH-boron nitride nanosheets (BNNS) forms a hydrogen-bond with the carbonyl group of PLLA, The hydroxyl group of OHâBNNS forms a hydrogenâbond with the carbonyl group of PLLA, contributing to improved dispersion of OH-BNNS in the polymer matrix
The polarizing microscope showed that a small amount of OH-BNNS could nucleate PLLA crystallization, forming small-sized showed that a small amount of OHâBNNS could nucleate PLLA crystallization, forming smallâsized spherulites
Summary
Boron nitride is a crystal composed of nitrogen atoms and boron atoms and contains four different variants, hexagonal boron nitride (h-BN), rhombohtic boron nitride (r-BN), cubic boron nitride (c-BN) and wurtzite boron nitride (w-BN), in which h-BN is very similar to graphite in structure, and commonly known as white graphite due to its own whiteness [1]. Few- and single- layered boron nitride nanosheets (BNNS) have attracted much attention due to their unique physical and chemical properties. Like other inorganic fillers [36,37,38,39,40,41], boron nitride can change the crystallization behavior of crystalline polymers. The effect of functionalized BNNS or exfoliated BNNS on crystallization behavior of polymers, especially PLLA, has not been reported in detail. The ball milling method assisted by NaOH aqueous solution for modifying boron nitride nanosheets was mild, simple and widely applicable [9]. Hydroxyl functionalized boron nitride nanosheets (OH-BNNS) were produced by chemical milling and mechanical shearing in the simple ball milling process. It was found that OH-BNNS greatly accelerated PLLA crystallization and influenced the crystal structure and macroscopic crystal morphology of PLLA as well
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