Papers by Author: Rui Jun Gao

Abstract: Polycarboxylate (PC) superplasticizer was synthesized by radical copolymerization using ammonium persulfate (APS) as initiator at 90 °C for 5 h. The effect of PC on the hydration process and microstructure of hardened cement at different hydration ages (4 h, 1 d and 7 d) was investigated. Hydration of cement paste results show that the nucleation and growth of hydration product of ettringite (Aft) was inhibited by PC at the early hydration ages, and the generation of the hydration products of calcium hydroxide (CH) and calcium carbonate (CaCO3) was promoted at late hydration ages. SEM result indicates that PC can make the structure of hardened cement more homogeneous and more density.

Abstract: Sulfonated β-cyclodextrin was synthesized with β–cyclodextrins (β-CD) and concentrated sulfuric acid. The molecular structure of sulfonated β-cyclodextrin was characterized by FTIR and ¹H-NMR. The dispersing ability of sulfonated β-cyclodextrin was investigated using various characterization methods like paste fluidity, adsorption amount and zeta potentials measurements. The results show that compared with sulphonated naphthalene based superplasticizer (NPS), the fluidity of cement paste dosage with sulfonated β-cyclodextrin is 248 mm, the zeta potential value changes from 11.5 mV to-19.6 mV with the concentration of sulfonated β-cyclodextrin increasing from 0 to 15 g/L and the maximum adsorption amount is 20 mg/g. Meanwhile, FTIR and ¹H-NMR results indicate that the sulfonic groups were grafted successfully on the molecular chain of the β-CD.

Abstract: The chitosan was degraded by hydrochloric acid and the effects of concentration of chitosan, amount of hydrochloric acid, reaction temperature and reaction time on the viscosity of chitosan were investigated. The results showed that the degraded chitosan with low viscosity could be prepared when chitosan (wt 6%) was dissolved in acetic acid solution and hydrochloric acid (wt 3%) at 90°C for 6 h to decrease the viscosity from 7.52 mPa·s to 2.48 mPa·s. Then, a graft copolymer was synthesized by copolymerization of degraded chitosan with methacrylic acid (MAA) and acrylamide (AAM) by using horseradish peroxidase (HRP)/H₂O₂/acetylacetone (ACAC) as initiator. The structures of original chitosan, degraded chitosan and the copolymer were characterized by FTIR. The copolymer was applied to the leather industry as an amphoteric retanning agent. The applied results showed that the retanned leather had the merits of good uniformity fullness softness, strong selecting filling properties, good dyeing ability and antimicrobial activity.

Abstract: The effect of sodium sulfate on the dispersion of polycarboxylate superplasticizer (PC) was studied in this paper. The study of fluidity of cement paste shown that the carboxyl groups did more to improve the fluidity of cement paste than the sulfonic groups, and a quick loss of fluidity was much more likely arisen by slufonic groups in PC comparing with the carboxyl groups. The methods of zeta potential and fluidity of cement paste were applied to investigate the dispersal ability of cement particles when different PC used in the present of different concentration of sodium sulfate. The result showed that the sulfonic group was more sensitive to sodium sulfate than carboxyl groups in PC.

Abstract: Superplasticizers with various of length of side chains, density of the carboxylic (-COO-) and sulfonic groups (-SO3-) have been synthesized based on different monomers and ratios. The effects of these structural factors on the properties of cement pastes were investigated though measurements of paste fluidity, adsorption amount and Zeta potential (ζ-potential). The results indicated that the higher density of -COO^- and -SO₃^- and the longer of polyoxyethylene (PEO) side chains contributed to the dispersion and adsorption amount of cement pastes in the presence of the same dosage of polycarbosylate superplasticizer. The results indicate that -COO^- and -SO₃^- mainly provide electrostatic repulsion effects and PEO side chains contribute to the steric hindrance repulsion during the process of hydration of cement.

Abstract: A graft copolymer was synthesized by means of radical copolymerization of degraded starch, phloroglucinol(PG) and sulfanilic acid (SA) and the reaction was catalyzed by horseradishperoxidase (HRP)/H₂O₂. It was discussed that the effectsof monomer composition, the temperature and system pH on the graft copolymerization. The ideal copolymer was synthesized in the pH 7.0 at 30°C when the molar ratio of PG and SA was 5:6. The structure of the copolymer was characterized by Fourier Transform Infrared (FTIR) spectroscopy. Meanwhile, the graft copolymer has been used in tanning process. The retanned leather exhibits excellent increase ratio in leather thickness and good dyeing ability which indicate that the graft copolymer has retanning and assisting dyeing properties.

Abstract: Modified starch tannage was synthesized by two steps. First step, a graft starch was synthesized by graft copolymerization of degraded starch with p-aminobenzene sulfonic acid and nekal using horseradish peroxidase (HRP)/H₂O₂ catalyze system. The effects of system pH, reaction temperature and amount of HRP on the graft efficient (GE) and graft percent (GP) were investigated and the maximum GE and GP of modified starch were obtained using 4 mg HRP/2.24 g H₂O₂ as catalyst at 35 for 3h under pH 7. The second step, the graft starch was oxidized by periodic acid to prepare modified starch tannage with dial dehyde.The effect of periodic acid on aldehyde groups content of graft starch was studied and it was found that the maximum content was at periodic acid concentration of 4 mol/L. The structure of modified starch tannage was characterized by FTIR, NMR and GPC. The shrink temperature (T_s)of tanned leather is 80.6 °C and the retanned leather has distinctive style of softness and flexibility.

Abstract: Two grafting starch was obtained by grafting copolymerization of two synthetical vinyl monomers using HRP/H2O2 as catalyst. The structure of vinyl monomers was verified by 1H-NMR.The grafting polymer was proof by structures were verified by FTIR. The effect of mass ratio of starch and vinyl monomer on the grafting efficiency (GE) and grafting percentage (GP) was studied. The highest GE and GP of the first grafting starch was 35% and 32%, 59% and 50% for the second grafting starch when the vinyl monomer ratio was 9%. The molecular mass tested by GPC for the two kinds grafting starch with highest GE and GP were 54 600 and 63 970. The two mostly grafted starches were used as retanning agent. The increase ratios in thickness were 18.1% and 18.6% respectively and the tanned leather has excellent softness and flexibility.