Md. Rezaul Karim Sheikh

Fiber length, thermal, mechanical, and dynamic mechanical properties of injection-molded glass-fiber/polyamide 6,6: Plasticization effect

Unreinforced- and glass fiber-reinforced-polyamide 6,6 specimens were subjected to dry, 50% RH, and wet conditions. FLD study showed that more fiber degradation occurred during processing of the composites with higher fiber loading. TGA results revealed that about 2% and 5% levels of moisture have been absorbed by the specimens subjected to 50% RH and wet conditions, respectively. From DSC results, with moisture uptake, there were no significance changes in the melting temperature, crystallization temperature, and enthalpy of crystalline; however, degree of crystallinity and enthalpy of melting decreased. Tensile strength, tensile modulus, flexural strength, and flexural modulus decreased with moisture uptake, while tensile strain and flexural displacement increased. DMA study showed that tan delta at room temperature and tan delta maxima increased with moisture absorption, while temperatures at maximum tan delta in α- and β-transition regions decreased.

The effect of terminal substituents on crystal structure, mesophase behaviour and optical property of azo-ester linked materials

ABSTRACT A series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH3, –OC2H5 and –OC3H7) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R12(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R22(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH3, –OC2H5 and –OC3H7) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λmax) of nearly 370 nm. GRAPHICAL ABSTRACT

Dyeing of Rajshahi silk with basic dyes: Effect of modification on dyeing properties

Abstract Colourfastness properties of degummed Rajshahi silk (Bombyx mori improved multi-voltine variety) were studied as a function of exposure to sunlight in air, washing with soap solution and spotting with acids and alkalis under different modifying and dyeing conditions. Study showed that 30% acetic acid and 20% tannic acid together was the best modifier for dyeing with Chrysoidine-Y, magenta, brilliant green, Victoria blue-β, Crystal violet and Auramine O basic dyes. Among the dyes, brilliant green exhibited best colourfastness under the prolonged exposure to sunlight in air. Washing with soap solution did not deteriorate colours at room temperature (27°C), but deterioration was observed with the increase of temperature. All the dyes used withstood their colours on silk to a great extent on washing with soap solution, although it slightly decreased with the increase of washing temperature. Spotting with acids and alkalis gave satisfactory results in most cases with the exception for sulphuric acid and sodium hydroxide. The tenacity of dyed silk was lower than that of undyed silk, but the loss in tenacity was higher under the exposure to sunlight in air.

Interfacial shear strength and tensile properties of injection-molded, short- and long-glass fiber-reinforced polyamide 6,6 composites

Injection-molded short- and long-glass fiber/polyamide 6,6 composites were subjected to tensile tests. To measure the effectiveness of the fibers in reinforcing the composites, a computational approach was employed to compute the fiber–matrix ISS, orientation factor, reinforcement efficiency, tensile-, and fiber length-related properties. Although the LFCs showed great improvement in fiber characteristics compared to the SFCs, enhancement in tensile properties was small, which is believed to be due to the larger fiber diameter. Kelly–Tyson model provides good approximation for the computation of ISS and tensile-related properties.

Synthesis and characterization of new copolymers from glycidyl methacrylate and tetrahydrofurfuryl acrylate: Determination of reactivity ratios

The new copolymers from different feed compositions of glycidyl methacrylate (GMA) and tetrahydrofurfuryl acrylate (THFA) were synthesized using free radical polymerization in toluene at 70±1 °C using benzoyl peroxide (BPO) as initiator. The polymers were characterized by 1H NMR, 13C NMR and FTIR spectroscopic techniques. The polydispersities of the copolymers suggest a strong tendency for chain termination by disproportionation. The glass transition temperature of the copolymers increases with increase in GMA content. The thermal stability of the copolymers increases with increase in THFA content. The copolymer compositions were determined using 1H NMR analysis. Reactivity ratios for GMA and THFA as determined by the Mao-Huglin method were r1=0.379 and r2=0.266. The results showed that all these copolymerizations are strictly linear systems describable by the Mayo-Lewis equation based on the terminal model and that accurate reactivity ratio data can be obtained.

New Homologues Series of Heterocyclic Schiff Base Ester: Synthesis and Characterization

A homologous series of liquid crystal bearing with heterocyclic thiophene Schiff base ester with alkanoyloxy chain (CH3(CH2)nCOO–, where , 6, 8, 10, 12, 14, 16) was successfully synthesized through the modification of some reported methods. The structural information of these compounds was isolated and characterized through some spectroscopic techniques, such as FTIR, 1H, and 13C NMR and elemental analysis. Textural observation was carried out using a polarizing optical microscope (POM) over heating and cooling cycles. It was found that all synthesized compounds (3a–g) exhibited an enantiotropic nematic phase upon the heating and cooling cycle with high thermal stability. Moreover, a characteristic bar transition texture was observed for compounds 3f and 3g which have shown transition of nematic-to-smectic C phase. This has been further confirmed by obtaining relative phase transition temperature using the differential scanning calorimetry (DSC).