Showing papers by "Jinyou Lin published in 2014"

Cellulose nanofibrils generated from jute fibers with tunable polymorphs and crystallinity

Abstract: Cellulose nanofibrils (CNF), as a kind of renewable, sustainable and biodegradable natural-based nanomaterial, have shown great potential application in numerous fields due to their fascinating properties. Some properties of CNF-based materials are closely related to their cellulose polymorph and crystallinity index. In this work, we present a facile method for the generation of CNF with tunable polymorphs and crystallinity via the alkali treatment of jute fibers under various conditions followed by (TEMPO)-mediated oxidation and mechanical disintegration. The changes of the cellulose polymorphs and crystallinity induced by alkali treatment on the jute fibers and consequently obtained CNF were well investigated by synchrotron radiation wide-angle X-ray scattering (SR-WAXS), Fourier transform infrared spectra (FTIR) and differential scanning calorimetry (DSC), respectively. Moreover, the morphology of the as-prepared CNF was also examined by transmission electron microscopy (TEM). It has been found that the CNF showed an identical cellulose polymorph to their source material, but a much higher crystallinity index, which revealed the feasibility of CNF generated from jute fibers with tunable polymorphs and crystallinity indexes.

Evolution of the microstructure and morphology of polyimide fibers during heat-drawing process

Abstract: The development of crystalline structure and morphology for polyimide (PI) fibers in the heat-drawing process was investigated by simultaneous synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). WAXD results indicated that the drawing process resulted in a high crystal orientation and ordered crystal structure. Especially, as the drawing ratio increases to 2.0, a well-defined crystalline structure forms in the fibers. We propose that the highly oriented molecular chains induce the formation of crystalline regions. Namely, an orientation-induced crystallization occur with stretching in the case of the heat-drawing polyimide fibers. The meridional scattering streaks in the SAXS patterns for the as-spun fibers suggest the presence of periodic lamellar structure in the fibers. These crystalline lamellae may evolve to more complete crystalline regions. The size of microvoids in the cross-section of the PI fibers is analyzed by SAXS. As a result, the drawing process leads to the orientation of microvoids along the fiber, and to reduced diameter of the microvoids in the fiber. Dynamic thermomechanical analysis indicates that the activation energy Ea of α relaxation increases with the increase in the crystallinity and orientation in the fibers.

Lamellae evolution of poly(butylene succinate-co-terephthalate) copolymer induced by uniaxial stretching and subsequent heating

Abstract: The lamellar structural evolution of biodegradable poly(butylene succinate-co-terephthalate) (PBST) random copolymer was investigated under the conditions of uniaxial stretching at 50 °C, and then heating from 50 to 150 °C at a strain of 150% by the in situ small-angle X-ray scattering (SAXS) technique. A long period referring to the lamellae while processing PBST was calculated, and a schematic for the structural evolution was proposed. It has been found that the lamellar structure experienced a remarkable transformation accompanied by the strain-induced melting of lamellae and formation of new lamellae when the strain exceeded 84% at 50 °C during the initial deformation process. After stretching by 150%, the lamellar structure remained unchanged with the perfection of lamellae in the subsequent heating process from 50 to 120 °C. Only at relatively high temperatures (120–150 °C), the long period of lamellae underwent a significant increase. Conclusions can be drawn that the lamellar structure of PBST is more sensitive to strain and only a relatively high temperature has a prominent impact on it, which is of great significance to provide targeted design guidance for the manufacturing and application of biodegradable PBST copolymer and also gives potential insights into other random and aliphatic–aromatic copolymers.