Soo Lee

Influence of Chemical Modification and Filler Loading on Fundamental Properties of Bamboo Fibers Reinforced Polypropylene Composites

The effects of chemical modification (silane coupling) and filler loading on the fundamental properties of the bamboo fiber (BF) filled polypropylene (PP) bio-composites were investigated in this study. Mechanical properties of the PP/ BF composites, such as the tensile strength, flexural strength, and impact strength decreased as BF loading increased. However, the tensile modulus, flexural modulus, and water absorption were increased by the increase of the BF loading. The addition of aminopropyltrimethoxysilane (AS) and tetramethoxy orthosilicate (TMOS) after the alkali pretreatment for the BF increased all the tensile, flexural, impact strength, and water desorption of the resultant composites, resulting from the improved adhesion between the BF and PP matrix. This tendency was more obvious with the increase of the BF loading. The melting temperature, melting enthalpy, crystallization enthalpy, and crystallinity were decreased by the increase of BF loading and the AS and TMOS treatments. One the other hand, the crystalline temperature was increased by the addition of the BF, AS, and TMOS. Hence, AS and TMOS are considered as effectual coupling agents for the PP/BF composite systems.

Effect of coagulation conditions on fine structure of regenerated cellulosic films made from cellulose/N‐methylmorpholine‐N‐oxide/H2O systems

The important properties of cellulosic fibers in the conditioned state are mainly influenced by fine structure. In particular, the development of new methods of spinning regenerated cellulosic fibers made from a cellulose/N-methylmorpholine-N-oxide (NMMO)/H2O system require a better understanding of their fine structures in order to explain their special physical properties. The regenerated cellulosic films were made from cellulose/NMMO/H2O according to the degree of polymerization and solution concentration (wt %) of cellulose and the concentration (wt %) of NMMO in the coagulation bath. The quantification of crystal content was carried out by the resolution of the wide angle X-ray diffraction intensity distribution on the assumption that all diffracted intensities take the form of a symmetrical Gaussian distribution centering at its Bragg angle. The X-ray diffraction patterns resolved into individual integral intensities showed that the polymorphic structure mixed with part cellulose III and II was obtained for only coagulated cellulose films. The degree of crystallinity and apparent crystalline size of regenerated cellulosic films depended on the degree of polymerization, the solution concentration of cellulose, and the concentration of NMMO. The diameter of the microfibril decreased with an increase in the concentration of NMMO.

Modified polyacrylonitrile blends with cellulose acetate: blend properties

Abstract Polyacrylonitrile (PAN) was modified by copolymerizing with methyl acrylate (MA) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS abbreviated as AP), and blended with cellulose acetate (CA) in dimethyl formamide. Scanning electron microscopy (SEM) showed much finer domain morphology for MA–PAN blends than AP–PAN blends. Dynamic mechanical property measurements showed an inward migration of the two glass transition temperatures ( T g ) viz., T g ’s of PAN and CA, however the migration of PAN T g was more pronounced in AP–PAN blends, the result agreed well with the conjugate phase calculation. The phase inversion composition, calculated using Coran–Patel model agreed well with SEM morphology.

Effect of methyl acrylate composition on the microstructure changes of high molecular weight polyacrylonitrile for heat treatment

The acrylate comonomer in polyacrylonitrile (PAN) precursor markedly influences the microstructure of PAN fiber and its resulting carbon fiber. In this study, the change occurring during the heat treatment of PAN copolymers (acrylonitrile-co-methyl acrylate) in the presence of air up to 260°C has been examined using both physical and chemical techniques. Considering the effect of the methyl acrylate content of PAN copolymers on the cyclization mechanism and fine structural changes in polymer chains under various heat treatment conditions, the composition of acrylonitrile and methyl acrylate = 98 : 2 to 97 : 3 mol % was suitable for the precursor preparation because the cyclization mechanism and fine structural changes in the boundary of this composition of copolymers were significantly different. With increasing MA content, the exothermic onset and peak in the thermogram was found to shift toward higher temperatures, and the aromaticity index decreased. This evidence indicates that MA was believed not to activate at all but to interfere with the cyclization. Additionally, by means of 13C nuclear magnetic resonance (13C-NMR) analysis, the tacticities of copolymers were nearly same, regardless of the copolymer composition, and the cyclization occurred nonstereospecifically during the initial heat treatment at 240°C for 1 h.

Mechanical and thermal properties of toluene diisocyanate-modified cellulose nanocrystal nanocomposites using semi-crystalline poly(lactic acid) as a base matrix

Although chemical modifications (grafting ‘onto’) of CNCs have been successfully adopted to enhance their dispersibility in apolar matrices and solvents, the problem of the dispersion level of mCNCs (chemically modified CNCs) in apolar matrices above a certain loading of nanoparticles remains an issue. CNCs were successfully modified using toluene diisocyanate, and the effects of the molar mass (Mw) and crystallinity (Xc) of semicrystalline poly(lactic acid) (PLA) on the mechanical and thermal properties of mCNC filled PLA nanocomposites were investigated. An increase in the mechanical properties of the PLA nanocomposites with mCNCs implied that Mw and Xc of PLA can be key factors to improve the dispersion level of mCNCs. In our solvent dilute polymer system, despite a reduction in the crystallinity of PLA with increasing mCNC loading level, the melting temperature of the PLAs remained constant due to the mCNC effect, which hinders the chain mobility of the PLAs. The results demonstrated that a fundamental understanding of the crystallinity and molar mass of polymers as well as surface modification of CNCs can be a reasonable approach to take full advantage of the potential usage of CNCs as reinforcements.

Physiochemical, optical and mechanical properties of poly(lactic acid) nanocomposites filled with toluene diisocyanate grafted cellulose nanocrystals

Although cellulose nanocrystals (CNCs) have been highlighted as a potential nano-reinforcement in polymer composites, the hydrophilic surface nature of CNCs limits their usage in the composite area due to the poor dispersibility of the CNCs in nonpolar solvent systems. A chemical modification of the CNCs was performed using toluene diisocyanate (TDI) to overcome the limitation in the solvent systems. CNCs and TDI-modified CNCs (mCNCs) reinforced poly(lactic) acid (PLA) films were prepared using the solvent casting method. After the modification, the mCNCs were well dispersed in chloroform with hydrophobic nature. In addition, AFM images and UV-Vis spectroscopy provide clear evidence for a good distribution of mCNCs in the PLA matrix. Thermal and mechanical behaviors of the PLA nanocomposite films with the CNCs and mCNCs were explored based on interfacial forces existing between the surface of the CNCs and the PLA matrix as well as the dispersibility of the CNCs with the increase of their loading levels.

Effect of NaOH Treatments on Jute and Coir Fiber PP Composites

Changes occurring in jute and coir fiber composites with 2–8% concentration of a NaOH treatment for 24 h were investigated, respectively, for void content, microscopy images, mechanical properties and water absorption. The jute and coir fibers were vacuum dried before molding composite specimens. Mechanical properties indicated good adhesion between natural fibers and PP. Jute fibers, when alkali-treated with 2% concentration for 24 h, showed best improvement in tensile strength by 40% and modulus by 9%, respectively, while coir fibers, when alkali-treated with 6% concentration for 24 h, showed best improvement in tensile strengths by 62% and modulus by 17%, respectively. With 2% concentration of alkali-treatments, the elongation of jute and coir composites reached 8% and 13.5%, respectively. Moisture absorption for jute and coir composites are 50% and 60% lower than untreated fiber composites, respectively.

Modified polyacrylonitrile blends with cellulose acetate: Fibers' properties

Fiber forming polyacrylonitriles (PAN) were modified by copolymerizing acrylonitrile monomer with methyl acrylate (MA) and 2-acrylamido-2-methyl propane sulfonic acid (AP), respectively, and blended with collulose acetate (CA). Fibers of MA-PAN, AP-PAN, and their blends with CA were wet-spun in dimethylformamide in a broad range of coagulation bath concentrations (CBC). The effects of hydrophilic and hydrophobic modification of PAN and the CBC, as well as the coagulation behavior, were studied in terms of morphology, mechanical properties, and water regain property of the fibers.

Influence of Allylamine Plasma Treatment Time on the Mechanical Properties of VGCF/Epoxy

The allylamine plasma treatment is used to modify the surface properties of vapor grown carbon fibers (VGCF). It is to improve the interfacial bonding between the VGCF and epoxy matrix. The allylamine plasma process was performed by batch process in a vacuum chamber, using gas injection followed by plasma discharge for the durations of 20, 40 and 60 min. The interdependence of mechanical properties on the VGCF contents, treatment time and interfacial bonding between VGCF/ep was investigated. The interfacial bonding between VGCF and epoxy matrix was observed by scanning electron microscopy (SEM) micrographs of nanocomposites fracture surfaces. The changes in the mechanical properties of VGCF/ep, such as the tensile modulus and strength were discussed. The mechanical properties of allylamine plasma treated (AAPT) VGCF/ep were compared with those of raw VGCF/ep. The tensile strength and modulus of allyamine plasma treated VGCF40 (40 min treatment)/ep demonstrated a higher value than those of other samples. The mechanical properties were increased with the allyamine plasma treatment due to the improved adhesion at VGCF/ep interface. The modification of the carbon nanofibers surface was observed by transmission electron microscopy (TEM). SEM micrographs showed an excellent dispersion of VGCF in epoxy matrix by ultrasonic method.

Mechanical Properties of VGCF/MAPP and Atmospheric Plasma-Treated VGCF/PP by Melt-Mixing Process

The effects of atmospheric plasma treatment and matrix modification by maleic anhydride PP (MAPP) addition, respectively, on the mechanical properties of vapor grown carbon fiber (VGCF)/polypropylene (PP) were investigated. Raw VGCF/PP, raw VGCF/MAPP, atmospheric plasma-treated (APT) VGCF/PP were melt mixed and extruded using a twin-screw extruder. The tensile modulus, shear modulus, and shear strength of APT VGCF/PP showed higher values than those of raw VGCF/PP. The tensile strength, flexural modulus, and flexural strength of raw VGCF/MAPP demonstrated higher values than all the other samples of raw VGCF/PP. The mechanical properties were improved with the atmospheric plasma treatment and coupling agent due to the improved adhesion at VGCF/PP interface. SEM micrographs revealed an excellent dispersion of VGCF in PP and MAPP, respectively. From the twin-screw extruder processing, the VGCF particles were relatively well aligned as well.