Preparation and Charactrization of Fibrous Crystals of Boron-containing MTW-type Zeolite

Fibrous crystals of boron-containing MTW-type zeolite have been hydrothermally synthesized in B2O3-SiO2-HF-H2O gel system at 170 ℃ in 20 to 28 d by using 1,4-diazabicyclo[2,2,2]octane (DABCO) and me-thylamine as the co-template, and characterized with XRD, SEM, TEM, HRTEM and SAED. The results of charac-terizations show that B atoms are incorporated into the zeolite framework as tetrahedron of B(OSi)4. The fibrous single crystals of 5—50 mm in length and 100—500 nm in width inter-grow along the c-axis of the zeolite, and the one dimension 12 oxygen ring channels are perpendicular to the fibber axis.

Improvement on the Mechanical Performance and Resistance Towards Hydrolysis of Poly(glycolic acid)via Solid-state Drawing

Poly(glycolic acid)is a biocompatible as well as biocomposable polymer with superior mechanical and barrier properties and,consequently,has found important applications in both medical and packaging fields.However,the high hydrolysis rate in a high humidity environment restricts its application.In this work,a solid-state drawing process after melt extrusion is applied in order to produce fibrous PGA with enhanced mechanical properties and a much better resistance towards hydrolysis.The crystal structure of PGA gradually transformed from spherulites into oriented fibrous crystals in the stretching direction upon solid-state drawing.Meanwhile,both the length of microfibril and the size of lamellae increased initially with the drawing ratio(DR),while the chain-folded lamellae transformed into extended-chain fibrils at high(er)DR.The oriented structures lead to an overall improvement of the mechanical properties of PGA,e.g.,the tensile strength increased from 62.0±1.4 MPa to 910±54 MPa and the elongation at break increased from around 7%to 50%.Meanwhile,the heat capacity of totally mobile amorphous PGA(∆C_(p)^(0)=0.64 J·g^(−1)·℃^(−1))was reported for the first time,which was used to analyze the content of mobile amorphous fraction(XMAF)and rigid amorphous fraction(XRAF).Both the oriented chain-folded lamellae crystals and the tightly arranged RAF are beneficial to prevent water molecules from penetrating the matrix,thus improving the resistance towards hydrolysis.As a consequence,the fibrous PGA with a DR of 5 showed a tensile strength retention rate of 17.3%higher in comparison with the undrawn sample after 7-days accelerated hydrolysis.Therefore,this work provides a feasible method to improve the mechanical and resistance towards hydrolysis performance of PGA,which may broaden its application and prolong the shelf-life of PGA products.