Preparation of high viscosity average molecular mass poly-L-lactide

Poly-L-lactide（PLLA） was synthesized by ring-opening polymerization fi＇om high purity L-lactide with tin octoate as initiator, and characterized by means of infi＇ared, and ^1H-nuclear magnetic resonance. The influences of initiator concentration, polymerization temperature and polymerization time on the viscosity average molecular mass of PLLA were investigated. The effects of different purification methods on the concentration of initiator and viscosity average molecular mass were also studied. PLLA with a viscosity average molecular mass of about 50.5×1^04 was obtained when polymerization was conducted for 24 h at 140℃ with the molar ratio of monomer to purification initator being 12 000. After purification, the concentration of tin octoate decreases; however, the effect of different purification methods on the viscosity average molecular mass of PLLA is different, and the obtained PLLA is a typical amorphous polymeric material. The crystallinity of PLLA decreases with the increase of viscosity average molecular mass.

The Influence of Different Land Use Manners on Soil Aggregate Characteristics of Consolidation and Returning to Field in Hollow Village of Hilly Area

The research aimed to explore the influence of different land use manners on soil aggregate,and provide scientific basis for improving soil stability and production performance of consolidation and returning to field in hollow village of hilly area. After consolidation and returning to field in hollow village of hilly area of Chengcheng County,Shaanxi,5 kinds of land use manners were set for 1-year plantation test,and they were corn( C treatment),wheat( W treatment),vegetable( V treatment),medicinal material( M treatment) and control( no plantation: CK treatment). Soil aggregate distribution,mean mass diameter( WMD),geometric mean diameter( GMD),aggregate failure rate( PAD),unstable aggregate number( ELT) and fractal dimension( D) at 0-40 cm of soil layer were measured and analyzed by dry and wet sieving methods. The results showed that( i) soil aggregate number and size at 0-40 cm of soil layer by each treatment were all significantly better than CK treatment,and > 0. 25 mm of aggregate content by dry sieving method( DR0. 25) and >0. 25 mm of aggregate content by wet sieving method( WR0. 25) at 0-40 cm of soil layer in each treatment showed declining trend with soil layer depth increased;( ii) MWD and GMD sequences of each treatment at 0-40 cm of soil layer by dry and wet sieving methods were both W treatment > C treatment > M treatment > V treatment > CK treatment,and C treatment was conducive to increasing large aggregate content of surface soil,while W treatment was conducive to increasing large aggregate content of lower soil;( iii) the analysis by wet sieving method showed that PAD and ELT at 0-40 cm of soil layer in each treatment both showed similar " Z" shape trend,and each treatment was significantly lower than CK;( iv) D sequence at 0-40 cm of soil layer in each treatment was C treatment < W treatment < M treatment < V treatment < CK treatment. D showed good linear relationship with> 0. 25 mm of aggregate content at 0-40 cm of soil layer by dry and wet sieving methods,and they were respectively R2= 0. 74 and R2= 0. 67. Corn and wheat plantation after consolidation and returning to field in hollow village was conducive to improving large aggregate content at 0-40 cm of soil layer,increasing the stability of soil layer and improving soil structure.

Effect of molecular structure and slump loss resistance of polycarboxylate superplasticizers on self-compacting concrete

A new kind of polycarboxylate superplasticizer with high slump loss resistance was obtained by designing scheduled molecular structure.The number average molecular mass of the polymer was characterized by the gel permeation chromatography measurements.And chemical structure of the polymer was observed by the Fourier transform infrared spectroscopy(FT-IR).The results show that the good workable maintaining of self-compacting concrete could be achieved through direct adjustment of number average molecular mass and different unsaturated monomer in synthetic process.The FT-IR analysis illustrated that the high slump loss resistance of polycarboxylate superplasticizers with ester and carboxyl group and expectations of molecular structure were designed.