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.

Bio-renewable polymers based on lignin-derived phenol monomers:Synthesis,applications,and perspectives

In recent decades,the continuous depletion of fossil fuels and the increasingly serious environmental issue have aroused wide attention on the development of biopolymers based on renewable biomass.Lignin is the second most abundant organic bio-based macromolecule second to cellulose,and it can be widely found in plants.Furthermore,various phenol derivatives can be obtained by their depolymerization processes.The development of bio-renewable polymeric materials originating from lignin-derivative phenol monomers,such as vanillin,syringaldehyde,eugenol,vanillyl alcohol,vanillic acid,and ferulic acid,will not only valorize the bio-sourced materials but also effectively reduce petroleum resource consumption and mitigate the environmental pollution.Therefore,an updated overview of the synthesis processes of these bio-based polymers developed in the past decade,which includes both thermosets and thermoplastics such as epoxy,phenolic,polyimine,polybenzoxazine,polyurethane,and polyesters,are elucidated.In addition,the applications of these bio-based polymers and their composites in flame-retarded materials,degradable and reprocessable materials,dielectric materials,optoelectronic materials,as well as smart responsive materials are also intensively discussed.In line with the gradual development of synthesis technologies,we believe that derivatives of lignin will turn into one of the most promising materials to be considered for the preparation of high-performance and functional bio-based polymer materials.