Laser cleaning of glass

The pulse lasers, YAG-, CO₂-, and N₂-lasers, are examined for use in the cleaning of glass. Cleaning is found to be due to the evaporation and sputtering of stains on the glass by the heat energy of the laser light. Only the N₂ laser can be used for the cleaning of the exit surface of the glass (the opposite side to the laser). A laser with a high peak power of about 10⁶J/s and short-pulse duration below 100 ns is found to be necessary in practice.     

Thermal stability of phthalate esters: Effect of substituents on the β-carbon atom

In order to clarify the mechanism conferring heat resistance on phthalate esters, those with a substituent on the β-carbon atom, such as bis(2-aminobutyl) phthalate, bis(2-nitrobutyl) phthalate, bis(2,4-diphenylbutyl) phthalate and dineopentyl phthalate, were synthesized and their thermal stabilities were studied by thermogravimetry and differential thermal analysis. The analytical results for these phthalate esters were compared with those for dibutyl phthalate, with a straight alkyl chain. As the temperatures required for a 3% weight loss of phthalate esters with a substituent, an electron-donating group (amino group) or an electron-accepting group (nitro group) on the β-carbon atom move to the higher end of the range, the effect of the adjacent group was recognized. The presence of a phenyl group in phthalate esters considerably improved the heat resistance. It is considered that the high heat resistance of bis(2,4-diphenylbutyl) phthalate is due to the obstruction of the planar configuration for cis elimination by the phenyl group and hindrance by the phenyl group of the formation of the six-membered cyclic transition state owing to the interaction between non-bondable molecules.     

Preparation and performance of plasticizers for poly(vinyl chloride) from products of thermal decomposition of waste polystyrene

2,4-Diphenylbutyl-2,4-diphenylbutyrate (DPBDPB) and 2,4,6-triphenylhexyl-2,4,6-triphenylhexoate (TPHTPH), plasticizers for poly(vinyl chloride), were synthesized from the products of thermal decomposition of waste polystyrene. Their heat stabilities were studied by thermogravimetric analysis and differential thermal analysis, and compared with those of typical plasticizers for PVC such as dibutyl phthalate (DBP), dihexyl phthalate (DHP) and bis(2-ethylhexyl) phthalate (DOP). DPBDPB and TPHTPH showed much higher heat resistance than DOP. PVC was plasticized with a mixed system consisting of DOP as the primary plasticizer and DPBDPB as the secondary. It became clear that DPBDPB is an excellent heat-resistant plasticizer which does not affect the compatibility of PVC with DOP.     

Studies on the thermal decomposition of phthalate esters: IX. Thermal decomposition of bis(2-ethylhexyl) phthalate

A flow apparatus equipped with a spray nozzle was developed for investigating the thermal decomposition of esters with high boiling points and viscosities. The thermal decomposition of bis(2-ethylhexyl) phthalate (BEHP), which is a typical plasticizer for poly(vinyl chloride) with a high boiling point and viscosity, was carried out by the use of the flow apparatus. The thermal decomposition products were analysed by gas chromatography and the kinetic parameters were calculated. The kinetic parameter of bis(2-ethylhexyl) phthalate was k_BEHP (s^?1)=4.59·10¹¹ exp(?40600/RT). From a comparison with the values for phthalic esters, it is proposed that a cis-elimination reaction takes place with a two-step mechanism in which the rate-determining step is α-carbon cleavage.     

Elution mechanism of polypeptides in reversed-phase liquid chromatography based on the critical threshold of organic solvent to induce abrupt change in adsorption capacity to the column packing

Adsorption capacity of polypeptides to the column packing in a solution containing multiple organic solvents was found to be expressed by means of an fn value, which is the sum of the ratios of the content of each organic solvent in the solution to the critical content of each organic solvent to cause abrupt change in the adsorption capacity, and to change abruptly at the point where the fn value becomes 1. Additionally, our results indicate that each polypeptide is eluted by the eluent containing a specific organic solvent content regardless of gradient elution rate in reversed-phase liquid chromatography, and that total organic solvent content in the eluent containing polypeptides is equal to the critical content. Considering the power law relationship between the retention times and the gradient elution rates, our results suggest that the elution of each polypeptide in reversed-phase liquid chromatography is mainly controlled by abrupt change in the adsorption capacity induced by change in the organic solvent content of the eluent during a gradient elution process, and that the abrupt change repeats across the critical threshold while a polypeptide moves through the column, and as a result, each polypeptide is concentrated in the eluent with the critical threshold.