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A degradable flocculant was prepared by natural renewable products (starch) and a cationic polymer. A cationic polyamine polymer was prepared by reaction of bis(hexamethylene)triamine with epichlorohydrin. The influence of substrate ratio and molecular weight of cationic polymer on flocculation was investigated and the optimum molecular weight was about 4000. Polyamine-modified starch flocculant was prepared by etherification reaction of cationic polyamine polymer and corn starch. The influence of substitution degree (DS) of starch on flocculation was investigated and the maximum DS was 0.18. The structure of starch-modified flocculant was characterized by XRD and the results confirmed that the plasticized samples contained some crystalline structures that were not destroyed by the etherification reaction process and some newly formed V-type crystalline structures were mainly induced by processing. Flocculation performance was evaluated in simulated kaolin suspension and was compared with that of commercial cationic polyacrylamide (CPAM) and polyaluminium chloride (PAC) flocculants. The flocculation effects of polyamine-modified starch flocculants and commercial flocculants under different dosages and pH values were compared. The results showed that the starch-modified flocculant had the best effect and the cationic starch derivatives flocculation performance increased with increasing DS, and exhibited steady flocculation performance to kaolin suspension in the broad pH range from 4 to 10. The preparation method of starch-modified flocculant is simple in preparation process, low in production cost and pollution-free, and facilitates industrial production.

The solubility of R-2[4-(6-chloro-2-benzoxazolyloxy)phenoxy]propanoic acid (abbreviated as Fenoxaprop-P) in acetone, methyl ethyl ketone (MEK), 1,4-butyrolactone, acetonitrile, DMF, isopropyl alcohol (IPA), n-butyl alcohol and THF were measured at temperatures ranging from 273.15 to 323.15 K at atmospheric pressure using a laser detecting system. First, the solubility data were correlated by the Buchowski–Ksiazczak λh equation and modified Apelblat equation. Compared with the Apelblat equation, the Buchowski–Ksiazczak λh equation can fit the solubility data well. Then, the dissolution enthalpy, entropy and Gibbs free energy of Fenoxaprop-P were predicted by the van’t Hoff and Gibbs equation.

The solubilities of R-(+)-2-(4-hydroxyphenoxy)propanoic acid (D-HPPA) in methanol, ethanol and various methanol-ethanol mixtures are determined in the temperature range from 273.15 to 323.15 K at atmospheric pressure using a laser detecting system. The solubilities of D-HPPA increase with increasing mole fraction of ethanol in the methanol–ethanol mixtures. Experimental data were correlated with Buchowski-Ksiazczak λh equation and modified Apelblat equation; the first one gives better approximation for the experimental results. The enthalpy, entropy and Gibbs free energy of D-HPPA dissolution in methanol, ethanol and methanol-ethanol mixtures were also calculated from the solubility data.