Crystallization kinetics of poly (L‐lactic acid)/montmorillonite nanocomposites under isothermal crystallization condition

Abstract

Poly(L-lactic acid)/o-MMT nanocomposites, incorporating various amounts of organically modified montmorillonite (o-MMT; 0-10 wt %), were prepared by solution intercalation. The montmorillonite (MMT) was organically modified with dilauryl dimethyl ammonium bromide (DDAB) by ion exchange. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that the o-MMT was exfoliated in a poly(L-lactic acid), (PLLA) matrix. A series of the test specimens were prepared and subjected to isothermal crystallization at various temperatures (T 1 -T 5 ). The DSC plots revealed that the PLLA/o-MMT nanocomposites that were prepared under nonisothermal conditions exhibited an obvious crystallization peak and recrystallization, but neat PLLA exhibited neither. The PLLA/o-MMT nanocomposites (2-10 wt %) yielded two endothermic peaks only under isothermal conditions at low temperature (T 1 ), and the intensity of Tm 2 (the higher melting point) was proportional to the o-MMT content (at around 171 C). The melting point of the test samples increased with the isothermal crystallization temperature. In the Avrami equation, the constant of the crystallization rate (k) was inversely proportional to the isothermal crystallization temperature and increased with the o-MMT content, especially at low temperature (T 1 ). The Avrami exponent (n) of the PLLA/o-MMT nanocomposites (4-10 wt %) was 2.61-3.56 higher than that of neat PLLA, 2.10-2.56, revealing that crystallization occurred in three dimensions.

Isothermal crystallization behaviors and kinetics of nucleated polylactide/poly(butylene adipate-co-terephthalate) blend films with talc

“…In addition, the PLA/PBAT/talc blends with different MDI contents displayed the range of n value between 2.42 and 2.79, indicating that the presence of PBAT, talc, and/or MDI led to the increment of n value of PLA. As shown in Table 2, the n value of neat PLA was closed to 2 representing the dimensionability of circular disk shape growth; on the other hand, the n values of all nucleated PLA blends were almost 3 suggesting the dimensionability of spherical growth [4]. The various amounts of MDI were hardly affected to the n values of the nucleated PLA blend films compared with neat PLA.…”

“…To overcome these drawbacks, many researches have been studied about PLA blending with a nucleating agent and a flexible polymer for improving the crystallization behavior and toughness of PLA. Many attempts have revealed that the nucleating agents such as modified montmorillonite (MMT), clay, and talc as well as the flexible polymer such as poly(e-caprolactone) (PCL) and poly(butylene adipate-co-terephthalate) (PBAT) have been well-worked with PLA [4,5,11,12]. One of the most widely studied and effective nucleating agents and flexible polymers for PLA modification are talc and PBAT, respectively, which have been used to enhance the crystallization rate, nucleation density, impact strength, and flexibility of the blends [5,11].…”

“…Generally, it is synthesized through ring-opening polymerization of lactides or direct condensation processes of lactic acid monomers which are derived from the fermentation of sugar feed stocks [1,2]. In the present, PLA is one of the most popular biodegradable polymers due to several excellent reasons; high mechanical strength, renewable product, biocompatibility, fully biodegradation within a few weeks, transparency, gas permeability, and easy processability [3][4][5]. According to these advantages, PLA which can be potentially applied in many fields such as tissue engineering, drug delivery system, automobile, food container, and film packaging becomes a promising and outstanding bio-based material for replacing petroleum-based plastics, e.g., polyolefins (PE and PP), polystyrene (PS), and poly (ethylene terephthalate) (PET) as well [6][7][8].…”

Bonding properties and crystallization kinetics of thermoplastic polyurethane adhesive

“…The reduction in n values indicates the interference of the additives in the crystal growth. The values of n range from 2.59 to 2.96, indicating threedimensional diffusion-controlled spherulitic crystal growth [17,18]. A lower n value can be identified for sample TPUC, which is visible in Figure 4, where the evident isothermal broadening curve is characteristic of low spherulite formation.…”

“…The crystallization half-time is the time required for 50% of the crystallization process to occur. [15,16] It is a very important crystallization kinetics parameter and it has been used to characterize the crystallization rate directly, the longer the t 1/2 , the slower the crystallization rate [17]. The crystallization half-time values are tabulated in Table 4.…”