Volume 34, Issue 7

The cationic copolymerization of 1,3-pentadiene (PD) with α-pinene (AP) initiated by aluminum trichloride (AlCl 3 ) was carried out in N -pentane solvent. The effects of the polymerization temperature and the comonomer composition on the yield of the copolymer, softening point, Gardner color scale and number-average molecular weight (Mn) are discussed. The performance of the copolymer was better than that of AP homopolymer (PAP) and PD homopolymer (PPD). The structure of the copolymer was characterized by Fourier transform infrared spectroscopy (FT-IR), 1 H-nuclear magnetic resonance ( 1 H-NMR), 13 C-NMR, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). In addition, the reactivity ratios for AP (M1) and PD (M2) determined by the Kelen-Tudos method from low-conversion data are r1=0.58 and r2=5.92, respectively.

Polyglycolic acid was synthesized by a one-step reaction of chloroacetic acid and triethylamine in tetrahydrofuran. The hydrolytic degradation of polyglycolic acid has been investigated. The in vitro degradation was investigated in a saline phosphate buffer. The degradation process was examined using Fourier transform infrared spectroscopy spectrum, weight loss, melting point, X-ray powder diffraction, pH, and scanning electron microscopy measurements. The chemical structure of polyglycolic acid has a small change during in vitro degradation. Degradation occurred with an increase in weight loss, a decrease in melting point, an increase in crystallinity during the initial degradation period and then a decrease afterwards. The melting point fell abruptly after the sixth week. This indicates that the degradation degree increased suddenly, i.e., the molecular weight of polyglycolic acid should decrease abruptly. The pH of the buffer solution fell quickly and decreased with time during in vitro degradation. The lower pH indicates that the molecular weight of polyglycolic acid synthesized by a one-step reaction should be low, and this may enable polyglycolic acid to degrade easily. As the degradation time increased, the surfaces of polyglycolic acid samples were highly degraded, and the surface porosity increased.

Three new mixed-type surfmers were synthesized using poly(propylene oxide)/poly(ethylene oxide)/poly(propylene oxide) (PPO-PEO-PPO) having terminal tertiary amine group as the basic material: (1) PPO-PEO-PPO with a carboxyl group on one end (MTA); (2) PPO-PEO-PPO with a quaternary ammonium group on one end (JTA); (3) PPO-PEO-PPO with a quaternary ammonium group on one end and a carboxyl group on the other end (MJTA). These products were confirmed by 1 H-NMR and FT-IR. Similar to PPO-PEO-PPO, the three surfmers have a cloud point (T cp ). Both MJTA and MTA have lower T cp than JTA. However, the cloud points of both MJTA-Na + and MTA-Na + are much higher than JTA. Their different T cp may be caused by their strength of dissociation in water. In addition, at a high temperature (T>T cp of MJTA), MJTA-Na + can be considered a pH-sensitive surfactant. At neutral and alkaline conditions, it can be used as an emulsifier. However, at acidic conditions, it loses its emulsification property. MTA-Na + has the same property.

Different generation hyperbranched polyurethanes (HBPUs) were synthesized through the A 2 +B’B 2 strategy. The molecular structures and viscosity were characterized by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The NMR results confirmed the formation of the branched units between the segments contained in the HBPU structure. The GPC with a four-capillary bridge design differential viscometer and the Ubbelohde viscometer showed a different viscosity. For the HBPUs, the viscosity first increased to higher values then decreased to lower values, and finally increased with increasing weight, which can be attributed to the spherical structure. The growth degree of HBPUs spherical structure depends on the forming hydrogen bonds; when the hydrogen bonds reach a certain degree, the spherical structure becomes compact.

Oxidized starch-graft-poly(styrene-butyl acrylate) [OS-g-P(St-BA)] latex was synthesized by the graft copolymerization of OS with St and n -butyl acrylate (BA) via emulsion polymerization. The graft copolymers were characterized by Fourier transform infrared (FT-IR), transmission electronic microscopy (TEM), dynamic light scattering, thermogravimetry (TG), and differential scanning calorimetry (DSC). The effects of the amount of OS, monomers, and initiator on graft copolymerization were investigated. Under the optimal conditions, the percentage of graft (PG), grafting efficiency (GE), and ζ potential could reach 256.5%, 41.7%, and -30.1 mV, respectively. The results indicated that the OS grafted onto particles greatly enhanced the colloidal stability of latex. The thermal stability properties of OS-g-P(St-BA) were also improved by the addition of OS. The OS-g-P(St-BA) latex may be used to partly replace the conventional synthetic latex for paper coating.

Four different peroxides as curing agents were used to prepare vulcanizates based on natural rubber (NR). The effects of temperature and peroxide concentration on the vulcanization characteristics of rubber compounds, cross-link density ( ν ) and physical-mechanical properties of equivalent vulcanizates were investigated. The results revealed that the vulcanization temperature and also the relative amount of peroxide decomposition products are of significant importance in the properties of vulcanizates. Lower vulcanization temperature and lower concentration of peroxides were found to be better factors, showing a proper balance between the degree of cross-linking of the rubber and degradation of the macromolecular chains by side reactions in relation to the crystallization of NR, which imparts vulcanizates based on NR outstanding properties.

The present work was an attempt to investigate the parameters that can affect the process of hydrogel formation in the presence of ultrasound. These parameters were concentrations of the reactants, the reaction medium, and acoustic factors. The monomers were acrylic acid and acrylamide, and the cross-linker was methylene bis acrylamide. Pulsed power ultrasound was irradiated to the reaction mixture from the tip of a probe unit. The swelling behaviors of the obtained hydrogels were investigated in various buffer solutions, at different temperature values, and using different ionic salts. The results show that ultrasonic irradiation significantly reduces reaction time and increases efficiency. Additionally, increasing glycerol in the solution changes the viscosity of the reaction for the better and increases the reaction rate. However, ionic strength and pH were not significantly effective in this respect. Another major finding was that increasing ultrasonic power and pulse hastens the reaction. Cationic salts were effective in this order: Na + >Ca 2+ >Fe 3+ . The hydrogel was responsive to pH, temperature, and salts. These findings provide a better understanding of hydrogel synthesis and enable us to control the pertinent parameters.

A new conductometric biosensor was developed and characterized; the biosensor was based on horseradish peroxidase that was deposited in chitosan and chitosan/AuNPs films. The biosensors were characterized by scanning electron microscopy and current-voltage curves. Current-voltage curves in biosensors showed that the electrical conductivity and bistability in biosensors can be modulated by horseradish peroxidase. Horseradish peroxidase catalyzed the reduction of H 2 O 2 to H 2 O with the oxidation of the prosthetic group (Fe 3+ ) in the enzyme to Fe 4+ =O. Conductometric signal in the biosensors increased with the gradual increase of H 2 O 2 concentration, and it was due to the H 2 O 2 reduction. Linear hydrogen peroxide detection was observed for a concentration between 0 and 15 m m . The results proved that these biosensors could have promising industrial applications, due to its rapid and sensitive H 2 O 2 detection.

This paper presents two separate methods to improve the tensile strength (TS) of textile waste cotton reinforced polymer composites (T-FRP) as prospective functional materials with respect to environmental concerns. Two very different methods were designed in order to improve the TS of the composite. In the first method, maleated anhydride polyethylene was added as the coupling agent into the composite composition, whereas in the second method, a totally new glass fiber and glass fabric laminated hybrid composite structure was designed. In this first study, the coupling agent was mixed up to 5 wt% into the composite structure in order to improve the bonding interface between low density polyethylene (LDPE) matrix and cotton waste fibers. The effect of the coupling agent was evaluated and compared with the unmodified one. By contrast, chopped glass (CG) fibers and woven biaxial glass fabrics were introduced into the composite layers with the intention of designing a new hybrid composite structure as a second study. The TS of the materials was evaluated and the fracture surface was assessed with an optical microscope. Consequently, an improvement in TS of 50% and 230% was achieved by the addition of the coupling agent and the creation of a new hybrid composite, respectively.

The effects of the filler content and its surface treatment on the tensile and flow properties of the polypropylene (PP) composites filled with wollastonite (CaSiO 3 ) were investigated. The results showed that the introduction of the filler could reinforce the PP resin, while the influence of the filler surface treatment on the tensile and flow property was insignificant. The melt volume flow rate (MVR) of the composites decreased nonlinearly, while the Young’s modulus increased nonlinearly with increasing filler weight fraction ( ϕ w ); the tensile strength and tensile fracture strength increased significantly when ϕ w was <10% and then decreased slightly with increasing ϕ w . The elongation at break decreased significantly when ϕ w was <10% and then decreased slightly with the increase of ϕ w . Moreover, the Young’s modulus was estimated using the equation published earlier, and a good agreement was shown between the predicted data and the measured data.

This work deals with the effect of the quenching temperature on the mechanical and thermophysical properties of polycarbonate (PC) pigmented with titanium dioxide (TiO 2 ). The thermal conductivity, thermal diffusivity, Izod impact strength and density measurements were measured. The thermal conductivity and diffusivity of the composites were measured using a periodic measurement method. It was found that an additional second quenching involved an increase in the value of the Izod impact strength near 35°C and a decrease in the values of the density, the thermal conductivity and the thermal diffusivity. A transition in these properties which is located at around 35°C has also been observed and linked to the β 1 relaxation mode of PC.

Currently, use of poly(lactic acid) (PLA) is limited for commercial applications because it has a low heat resistance. In this research, an increase of over 40°C heat distortion temperature (HDT) of PLA alloy was obtained by blending PLA with polycarbonate (PC) and a chain extender (CE). Molecular weight, thermal, mechanical and morphological properties of PLA and PC blend with different CE contents were investigated. Gel permeation chromatography (GPC) results showed that some PLA-PC copolymers were produced and the compatibility of the PLA phase and in the PC phase was improved via the chain extension reaction. In addition, the reaction induced by CE also affected the crystallization behaviors of PLA, as observed from differential scanning calorimetry (DSC) results and the enthalpy of melting of PLA decreased with increasing CE content. The combined effects of the CE increasing molecular weight, improving compatibility and limiting the crystallization behavior of PLA/PC alloy greatly improved the HDT.

This study investigated the use of ultrasonic technology in assisted injection molding (AIM) and mold design. An ultrasonic device installed in a mold was employed to vibrate a melt, thereby converting kinetic energy into thermal energy. This method enabled maintaining the desired temperature in the melt flow, preventing a high level of shear and the formation of a thick frozen layer surrounding the skin layer; thus, the injection molding efficiency was enhanced and the residual stress inside the injection-molded component was reduced. In this study, a flat sample (75 mm×47 mm×1 mm) of an ultrasonic-assisted injection mold was developed. An ultrasonic oscillation device 45 mm in diameter was placed in the center of the cavity and used to vibrate a polycarbonate melt at a frequency of 20 KHz. In addition, cavity pressure sensors were positioned at the front and rear of the vibration region to analyze the melt flow behavior under ultrasonic-AIM (UAIM) conditions. The results showed that ultrasonic oscillations can reduce the amount of melt pressure lost through the cavity. The pressure loss of the flat sample used in UAIM was approximately 29% lower than that of the sample used in conventional injection molding (CIM; nonultrasonic-assisted injection); the power of UAIM did not yield substantial effects. Direct ultrasonic oscillations destroyed the melt flow and thermal stresses, therefore, the region exhibited a low stress distribution. Compared with using CIM, using UAIM reduced the average residual stress by 27%. Ultrasonic oscillation affected the surface roughness during melt solidification. When the ultrasonic power was <70%, no substantial increase in surface roughness was observed; however, when the ultrasonic power >70%, the surface roughness was 10 times higher compared with that observed using CIM.