ABSTRACT:The thermal degradation kinetics of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [poly(HB-HV)] under nitrogen was studied by thermogravimetry (TG). The results show that the thermal degradation temperatures (T o , T p , and T f ) increased with an increasing heating rate (B). Poly(HB-HV) was thermally more stable than PHB because its thermal degradation temperatures, T o (0), T p (0), and T f (0)-determined by extrapolation to B ϭ 0°C/min-increased by 13°C-15°C over those of PHB. The thermal degradation mechanism of PHB and poly(HB-HV) under nitrogen were investigated with TG-FTIR and Py-GC/MS. The results show that the degradation products of PHB are mainly propene, 2-butenoic acid, propenyl-2-butenoate and butyric-2-butenoate; whereas, those of poly(HB-HV) are mainly propene, 2-butenoic acid, 2-pentenoic acid, propenyl-2-butenoate, propenyl-2-pentenoate, butyric-2-butenoate, pentanoic-2-pentenoate, and CO 2 . The degradation is probably initiated from the chain scission of the ester linkage.
Microwave‐assisted extraction (MAE) was utilized to extract tea saponin from oil‐tea camellia seed cake. The factors influencing the extraction efficiency were studied, including the effects of microwave power, irradiation duration, temperature, ratio of solvent to material and aqueous ethanol concentration. By systematic orthogonal experiments, the optimal extraction technology was determined. Compared with a conventional extraction method, MAE shows great advantages with the extraction time reduced from 6 h to 4 min, 50 % organic solvent saved and about 14 % extraction yield enhanced. Fourier transform infrared spectroscopy testing and high performance liquid chromatography analysis proved that the extracted resultants were tea saponin with similar compounds as a standard tea saponin. The extracted tea saponin was applied on the cleaning of historic silks and showed good removal effect on the stains. This work provides useful information for fully use of oil‐tea camellia seed cake and new applications of tea saponin at the protection of historic textiles.
The effect of a floating stearate monolayer on the formation of Mg-Al-hydrotalcite (Mg-Al-LDH) has been studied. A subphase was an aqueous solution of Mg(NO3)2‚6H2O (1.6 × 10 -3 M) and Al(NO3)3‚6H2O (5.3 × 10 -4 M) adjusted at pH ) 10.5 by 1.0 M NaOH. Templating effects were studied in the following two ways. First, we spread a chloroform solution of stearic acid onto the above subphase and waited 6 h at zero surface pressure (0.51 nm 2 molecule -1 ). After the surface was compressed to 20 mN m -1 (0.26 nm 2 molecule -1 ), the floating film was deposited onto mica as a Z-type film (method 1). Second, we spread the same chloroform solution onto the subphase and started to compress the surface to the molecular area (0.40-0.20 nm 2 molecule -1 ) after 30 min. The floating film was maintained at the constant surface pressure for 6 h. Thereafter, it was deposited onto mica as a Z-type film (method 2). From the atomic force microscope (AFM) images of the films, it was concluded that the largest thin crystals (ca. 3 × 10 µm) with the thickness of 10 ( 1 nm were obtained according to method 2 when the deposition was done at 0.36 nm 2 molecule -1 (0.78 mN m -1 ). This optimum molecular area was close to the area occupied by one negative charge for 3:1 Mg-Al-LDH (0.34 nm 2 ). From the X-ray diffraction measurements and elemental analyses, the deposited films prepared by both methods were suggested to be Mg-Al-CO3 2--LDH. As a comparison, a 0.1 mL portion of the subphase solution, which had been aged for 6 h, was cast onto mica and dried under the air. The AFM image of such a cast sample showed noncrystalline aggregates of small particles with the diameter of 0.2-3 µm. These results indicated that a stearate monolayer acted as a template for the crystallization of Mg-Al-LDH at an air-water interface.
Thermal analyses of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-HV)], and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB-HHx)] were made with thermogravimetry and differential scanning calorimetry (DSC). In the thermal degradation of PHB, the onset of weight loss occurred at the temperature (°C) given by T o ϭ 0.75B ϩ 311, where B represents the heating rate (°C/min). The temperature at which the weight-loss rate was at a maximum was T p ϭ 0.91B ϩ 320, and the temperature at which degradation was completed was T f ϭ 1.00B ϩ 325. In the thermal degradation of P(HB-HV) (70:30), T o ϭ 0.96B ϩ 308, T p ϭ 0.99B ϩ 320, and T f ϭ 1.09B ϩ 325. In the thermal degradation of P(HB-HHx) (85:15), T o ϭ 1.11B ϩ 305, T p ϭ 1.10B ϩ 319, and T f ϭ 1.16B ϩ 325. The derivative thermogravimetry curves of PHB, P(HB-HV), and P(HB-HHx) confirmed only one weight-loss step change. The incorporation of 30 mol % 3-hydroxyvalerate (HV) and 15 mol % 3-hydroxyhexanoate (HHx) components into the polyester increased the various thermal temperatures T o , T p , and T f relative to those of PHB by 3-12°C (measured at B ϭ 40°C/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70°C.
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