Kasinee Hemvichian

Thermal decomposition processes in aromatic amine-based polybenzoxazines investigated by TGA and GC-MS

Abstract Three different aromatic amine-based polybenzoxazines are subjected to thermal decomposition in a thermogravimetric analyzer. The degradation products, which are volatile compounds evaporating out of the furnace as gases, are trapped and analyzed further by a gas chromatograph which is coupled with a mass selective detector (GC–MS). All the degradation products are separated by GC and come out at different retention times, as seen in the total ion chromatogram. All the compounds mass are selectively identified by MS. The chromatograms are divided into two regions; the low column temperature region containing low molecular weight and highly volatile compounds, and the high column temperature region containing higher molecular weight and less volatile compounds. The evolved gas analysis performed by GC–MS allows us to identify the molecular weight and also the structure of the volatiles. This information is then used to illustrate the processes occurring during the thermal decomposition of aromatic amine-based polybenzoxazines.

Thermal decomposition processes in polybenzoxazine model dimers investigated by TGA-FTIR and GC-MS

The thermal decomposition processes of a model compound containing Mannich bridge and a series of polybenzoxazine model dimers are investigated using TGA–FTIR and GC–MS. The 2,4-dimethylphenol-based benzoxazine dimers degraded into smaller and highly volatile compounds, leaving no char at the end of degradation. The p-cresol-based benzoxazine dimers degraded into smaller and highly volatile products as well, nevertheless some of which are able to undergo crosslinking and aromatization processes and form char. The major decomposition products for modified p-cresol-based dimers are amines and ester compounds. # 2002 Published by Elsevier Science Ltd.

Shape memory polymers from benzoxazine-modified epoxy

Novel shape memory polymers (SMPs) were prepared from benzoxazine-modified epoxy resin. Specimens consisting of aromatic epoxy (E), aliphatic epoxy (N), Jeffamine D230 (D) and BA-a benzoxazine monomer (B) were evaluated. The mole ratio of D/B was used as a mixed curing agent for an epoxy system with a fixed E/N. The effects of BA-a content on the thermal, mechanical and shape memory properties of epoxy-based shape memory polymers (SMPs) were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), flexural test and shape recovery test. The results revealed that the obtained SMPs exhibited a higher flexural strength and flexural modulus than those of the unmodified epoxy-based SMP at room temperature and at 20?? C above glass transition temperature (Tg). The presence of 1?mol BA-a as a curing agent provided the specimen with the highest Tg, i.e. about 72?? C higher than that of epoxy-based SMP cured by Jeffamine D230. All SMP samples needed only a few minutes to fully recover to their original shape. The samples exhibited high shape fixity (98?99%) and shape recovery ratio (90?100%). In addition, the recovery stress values increased with increasing BA-a mole ratio from 20 to 38?kPa, when BA-a up to 1?mol ratio was added. All of the SMP samples exhibited only minimum change in their flexural strength at the end of a 100 recovery cycles test.

The effect of polymerization conditions on the density and Tg of bisphenol-A and hexafluoroisopropylidene-containing polybenzoxazines

The volumetric expansion of bisphenol-A and aniline-based benzoxazine (BA-a) has been studied by comparing the room temperature density of the cured BA-a under different polymerization conditions with the amorphous BA-a monomer. The glass transition temperatures (Tg) of BA-a at various degrees of polymerization have been investigated by differential scanning calorimetry (DSC). The degrees of conversion at different polymerization temperatures were compared with the respective glass transition temperatures. It was found that substantial development of Tg occurs at low degrees of conversion. A fluorinated polybenzoxazine was synthesized from the ring-opening polymerization of hexafluoroisopropylidene-containing benzoxazine monomer. The properties of the fluorine-containing polymer were compared to those of nonfluorinated polybenzoxazine. Fluorine incorporation had a profound effect on the glass transition temperature of polybenzoxazine. The thermal stability also improved upon fluorination.

Ultrathin Film Formation by Gamma-Ray Induced Polymerization in Surfactant Template on Solid Surface

Ultrathin film of polyisoprene was formed on silica surface in the two dimensional adsorbed surfactant by gamma-ray induced polymerization. The effect of gamma irradiation total doses on polymeric film formation was investigated. The modified silica and formed film were characterized. The results showed the potential of the surface modification by polymer film-surfactant-silica hybrid.

Effects of Electron Beam on Irradiated Polyimide/Polyaniline Composites

In this study, the composites prepared from polyimide (PI) and polyaniline (PANI) were radiated with electron beam (EB) at the radiation doses of 0, 50, 150, 200, and 300 kGy. The electrical conductivity and thermal properties of the radiated composites were determined and compared with those of the composites doped with 6M HCl. The results revealed that the electrical conductivity was enhanced from 3.42 x 10-16 S/cm (untreated polyimide without polyaniline) to 6.97 x 10-5 S/cm when the PI/PANI composite was doped with HCl at 10 phr of PANI; furthermore, the conductivity was increased to 2.16 x 10-4 S/cm for the composite at 10 phr of PANI with radiation dose of 200 kGy. In addition, it was found that the glass transition temperature of the composite was increased with the increase of PANI content for either EB radiation method or protonic acid doping method. It could be noted that the electrical conductivity values of the radiated composites were higher than those of composites doped with HCl at the same PANI content.

Thermal Degradation Kinetics of Polyurethane/polybenzoxazine Alloys

Recently, the alloys of polyurethane (PU)/polybenzoxazine (PBA-a) have been studied due to many interesting properties; however, the thermal degradation kinetics of the system has not been mentioned before. In this study, the degradation temperatures of the obtained alloys were determined using Thermogravimetric Analyzer (TGA) with various heating rate of 10, 20, 25oC/min. The polyurethane /polybenzoxazine alloys at the weight ratios of 30/70 were prepared for determination due to its highest degradation temperature. The first derivative curves of the thermograms (DTG) were deconvoluted with Peak-fit program. The results reveal three main sub-stages of degradation. According to Arrhenius Eq., the activation energies (Ea) of each degradation sub-stage were determined using Kissinger model and Fynn-Wall Ozawa model.

Effects of Gamma Radiation on Thermal and Mechanical Properties of Wood-Flour Filled Polybenzoxazines

In this study, the composites for wood substitution made of benzoxazine filled with rubber wood-flour were fabricated. The wood flour contents was varied from 0 to 30 wt%. The effects of gamma radiation on the thermal and mechanical properties of wood-flour filled polybenzoxazine were determined. The different radiation dose (i.e. 0, 10, 20, and 30 kGy) was applied to the fabricated samples. The differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA) were used to evaluate glass transition temperature (Tg) and degradation temperature (Td), respectively. While the flexural strength was determined using Universal Testing Machine (UTM). It could be noted that the increase of radiation dose provided the decrease of Td. Moreover, the values of Tg, flexural strength, and water absorption reveals the similar trend with the maximum point at 20 kGy of radiation dose.

Effects of Gamma Radiation on Thermal Properties of Benzoxazine Filled with Carbon Black

In this study, the mixtures between benzoxazine monomer and electrically conductive carbon black (CB) were radiated with gamma ray at different doses, i.e. 0, 25, 50, 75, and 100 kGy before polymerization. The contents of carbon black filler were varied i.e. 0, 5, and 30wt%. The thermal properties such as curing temperatures and glass transition temperatures were determined using differential scanning calorimeter (DSC), while the decomposition temperature and char yields were analyzed using thermogravimetric analyzer (TGA).The results reveal that the radiation could decrease the curing temperature of pure polybenzoxazine. In addition, the decomposition temperature and char yield were increased with the increase of CB content. At the same CB content, the radiation dose could decrease the decomposition temperature and char yield.

Mechanical Properties of Poly(lactic acid) / Thermoplastic Starch Blends Crosslinked by Gamma Radiation

This research aims to determine the influences of radiation-induced crosslinking on the mechanical properties of polymer blends between poly (lactic acid) (PLA) and thermoplastic starch (TPS). PLA and TPS were mixed at different ratios (90:10, 80:20, 70:30, 60:40) in the presence of a crosslinking agent using a twin screw extruder. The blends were compression molded into films. The film samples were irradiated by gamma radiation at different doses. Gel fraction was used to determine crosslinking efficiency. Results showed that gamma radiation was able to induce crosslinking for PLA/TPS blends. The gel fraction and mechanical properties decreased with increasing TPS content. The optimum ratio of PLA:TPS with the maximum gel fraction and mechanical properties was 90:10 and the optimum dose was 40 kGy by gamma radiation.