私密直播全婐app免费大渔直播,国产av成人无码免费视频,男女同房做爰全过程高潮,国产精品自产拍在线观看

T. Wang, X. Ma, L. Zhang, and G. Cheng*

School of Materials Science and Engineering, Tianjin University, Tianjin, 300072, China

Poly(3-hydroxybutyrate)(PHB) is a well-known biodegradable thermoplastic polymer for many application^[1]. However, its applicability is somewhat limited because it is brittle with a low elongation and it is easily degraded at the temperature slightly higher than its melting point. Blending of PHB with other polymer has also been studied extensively. These polymers include poly(ethylene oxide)(PEO), poly(vinyl acetate) (PVAc), cellulose acetate butyrate (CAB) etc^[2-4]. In order to get the blends that can be completely degradable, study on blends of PHB with degradable polymer is our research direction. Our team have studied the PHB/CAB, PHB/PEO and PHB/PEO/CAB blends. Our purpose is to find the relationship between the blend morphology and physical properties, but more important is to seek a means of making the best use of the degradable polyester.

In this paper, A two-step procedure was used to synthesize CAB and poly(ethylene glycol) graft copolymer (CAB-g-PEG). Hydroxyl end groups of PEG are reacted with 2,4-toluene diisocynate (TDI) to get the prepolymer NCOPEG with isocynate end groups, then grafting of NCOPEG on the CAB. By choosing the appropriate composition, the cross linked graft copolymer or not could be obtained. Then the CAB-g-PEG copolymer was blended with PHB to further improve the mechanical properties of PHB. The crystallization behavior, mechanical properties, and environmental biodegradability of PHB/ CAB-g-PEG blends were studied in detail. As the CAB-g-PEG copolymer increased in the PHB/ CAB-g-PEG blends, the cold crystalline temperature of the blends increased, the degree of crystalline of PHB decreased, the melting peak became broaden and T_m slightly decreased. These results indicated that the crystallization of PHB was hindered and more imperfect crystals of PHB in the blends. The tensile properties and impact strength of the PHB/ CAB-g-PEG blends were superior to the PHB/CAB blends. The PHB/CAB-g-PEG blends could be degradable in natural environment and would not bring pollution.

The Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE (2002-123) and the Natural Science Foundation of Tianjin (003801111) support this research work.

[1]     Cai Z, Cheng G, 2002. Chinese J. Biomed. Eng. 11(4), 166-170.

[2]     Avella M, et al., 1991. Polymer 32(9), 1647-1653.

[3]     Yuxian A, et al., 1999. Eur. Polymer J. 35, 365-369.

[4]     Tiezhu W, et al., 2003. J. Appl. Polymer Sci. 89(8), 2116-2122.

        論文來源：International Symposium on Biological Polyesters ,Auguest 22-27, 2004