Abstract
The role of organic solvents in governing the crystallization and morphology of semi-crystalline poly-l-lactide (PLLA) sheets was systematically investigated. Three different organic solvents; ethyl acetate (EA), o-dichlorobenzene (ODCB), and nitrobenzene (NB), with a solubility parameter analogous to PLLA and with a high capability of swelling, were chosen. It has been witnessed that the degree of crystallization and crystal morphology depends highly on the degree of swelling and evaporation rate of the solvent. Besides, the temperature and time of treatment played a significant role in the crystallization of polymers. The effect of different solvents and curing times are reflected by the measured X-ray diffraction (XRD) peaks and the differences are best shown by the unit cell size. The largest variation is observed along the c-axis, indicating shorter bonds, thus, showing better conformation after NB and ODCB treatment. The percentage of crystallinity calculated using the classical relative crystallinity index of XRD shows closer values to those calculated with differential scanning calorimetry (DSC) data, but a huge variation is observed while using the LeBail deconvolution method. The strong birefringence of polarised optical micrograph (POM) and the crystal morphology of scanning electron micrograph (SEM) also evidenced the orientation of polymer crystallites and increased crystallinity after solvent-supported heat treatment.
Highlights
Due to the depletion of fossil fuels and the huge environmental impact of extraction methods, the production of plastics from such fossil fuels is not a sustainable way to do so [1], and their wastes, discarded into the environment, are subject to slower degradation
This second approach is not commonly used in polymer X-ray diffraction (XRD), the amorphous fraction was modelled with a Pawley single or multiple peaks, as the deconvolution required, and from the obtained crystalline to amorphous ratio, the crystallinity percentage was determined. This second approach is not commonly used in polymer XRD, we have found we have found that it could give more accurate results, since it incorporates crystal structure-based peak broadening due to crystallite size, it accounts for a crystalline fraction in the border of the microcrystalline-amorphous region
Facilitates the smooth solvent molecules into the whichisstimulates the This random movement of thediffusion polymer of molecular chain, thereby the matrix, which stimulates the random movement of the polymer molecular chain, thereby inducing the orderly arrangement of chains with a high degree of crystallinity
Summary
Due to the depletion of fossil fuels and the huge environmental impact of extraction methods, the production of plastics from such fossil fuels is not a sustainable way to do so [1], and their wastes, discarded into the environment, are subject to slower degradation. Biodegradable polymers are the potential replacement for petroleum-based polymers and other bio-compatible materials, such as metals and ceramics [2]. The most widely using biodegradable polymers are polylactide (PLA), polycaprolactone (PCL), poly(butylene adipate terephthalate) (PBAT) and polyhydroxybutyrate (PHB) [3]. PLA is one of the major commercial biopolymers derived from renewable raw materials such as corn starch, potato, sugarcane and even from food wastes [4]. The PLA has been widely used in the packaging industries due to its biodegradability, good mechanical and Polymers 2020, 12, 1065; doi:10.3390/polym12051065 www.mdpi.com/journal/polymers. Polymers 2020, 12, 1065 translucent properties [5]. Special grades of PLA had been developed for biomedical applications such as drug delivery systems [6]
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