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In order to explore an effective method to improve the adsorption property of maize starch granules, ultrasonic pretreatment at different temperatures (0, 25, 45, and 65 ℃) below the gelatinization temperature combined with α-amylase was used to modify maize starch. The results showed that after ultrasonic pretreatment, the surface of starch granules became rough with grooves on it. The molecular mass, relative crystallinity and short-range molecular order of the starch samples were significantly decreased (P < 0.05). Compared with single enzymatic hydrolysis, the combinatorial treatment increased the specific surface area and pore capacity of starch consequently improving its adsorption performance. With an increase in the pretreatment temperature from 0 to 65 ℃, the water- and oil-adsorbing capacities of starch granules subjected to the combinatorial treatment increased from 114.71% and 142.16% to 144.77% and 189.70%, respectively. Therefore, ultrasonic treatment at high temperature below the gelatinization temperature combined with α-amylase could be an effective method to prepare a green and high efficiency starch-based adsorbent. This study will be helpful for better understanding of the mechanism by which ultrasonic treatment promotes the enzymatic hydrolysis of starch and will provide a theoretical basis for the development of high-efficiency starch-based adsorbents.

This study was carried out in order to explore the effect of ultrasonic treatment at different temperatures (0, 20, 40 and 60 ℃) on the ability of maize starch to form a complex with lipid. Scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), X-ray diffractometry (XRD), laser confocal micro-Raman spectroscopy and were used to characterize the changes in the multilevel structure of maize starch granules before and after treatment, and the mechanism for the change in its lauric acid complexing capacity was analyzed. The results showed that the lipid complexing capacity of maize starch was significantly (P < 0.05) reduced by ultrasonic treatment, and the complexing index decreased from 27.9% to 15.0% with increasing temperature from 0 to 60 ℃; the enthalpy change (ΔH), relative crystallinity, degree of short-range order and relative content of resistant starch declined. Through the multi-level structure analysis, it was found that the molecular chain of the starch was depolymerized by ultrasonic treatment, and ultrasonic treatment at 60 ℃ caused the leaching of amylose from starch granules, thereby damaging their integrity and making the surface rough. In conclusion, ultrasonic treatment at different temperatures can reduce the lipid complexing capacity of starch by changing its multilevel structure.

The strength and sealing failure of the connecting thread of the casing head mandrel hanger causes huge economic losses. One of the major challenges is the thread seal failure mechanism of the casing hanger in the wellhead during pressure testing in shale gas wells. In order to analyze the failure causes of connecting threads and put forward improvement measures, a typical case of a well accompanied by a hanger seal failure is analyzed in this paper, and a series of material tests are carried out. The microstructure and mechanical properties of casing materials and hanger materials could meet the field requirements. It is concluded that both the hanger material and casing material are characterized with significant ductile fracture. A three-dimensional model of the hanger and casing system is established, and the mechanical behavior is calculated for the connecting thread under different working conditions. The results showed that the connection degree of the hanger–casing is insufficient at the torque recommended by the manufacturer because of the difference in wall thickness between the box thread of the hanger and the box thread of the joint according to the connection degree of the coupling casing. It is seen that the high contact pressure ring of zone three on the sealing surface plays an effective sealing role under the manufacturer's recommended torque (20,465 N·m). Finally, when the torque is increased by 25%, the maximum contact pressure between the pin thread of the casing and the box thread of the hanger can fully meet the internal pressure from the wellbore pressure test and the internal pressure strength required for subsequent operations. [ABSTRACT FROM AUTHOR]