Evolution of phase behavior and orientation in uniaxially deformed polylactic acid films

Abstract

The development of crystalline structure and orientation during uniaxial stretching of cast amorphous linear and branched lactic acid films were investigated in the rubbery temperature ranges that spans between glass transition temperature and cold crystallization temperature. This material exhibited almost ideal stress‐strain behavior in the temperature range 65–80°C. Because of its strain crystallizability, films with uniform thickness can be obtained at high deformation levels as a result of self‐leveling. Branching was found to retard this self‐leveling through its slightly detrimental effect on the strain hardening. Upon stretching the material undergoes rapid orientation in the amorphous state and beyond a critical level very sharp and highly oriented β crystalline form chains with −3/1 helix. If the temperature is at or below Tg, with additional stretching, the films were found to revert to a highly oriented amorphous state through the destruction of the crystalline domains. At higher temperatures, further stretching results in continuation of improvement in crystalline order.

Effect of the simultaneous biaxial stretching on the structural and mechanical properties of PLA, PBAT and their blends at rubbery state

“…The enhancement of the crystallization behavior and the increasing of crystallinity have been widely discussed in the literature. It has been reported that the high crystallinity can be achieved by isothermal annealing [7], polymer blending [8], addition of nucleating agents [9] and strain-induced crystallization [10,11].…”

Biodegradable polylactide/hydroxyapatite nanocomposite foam scaffolds for bone tissue engineering applications

“…The CCT curves were assumed to provide some indication of the crystallization rates during the foaming process, although one should bear in mind: (i) the possible plasticizing effect of residual dissolved CO 2 after depressurization [41,55,56]; (ii) that the temperatures measured inside the autoclave did not necessarily give a precise indication of the local temperatures within the PLA; (iii) the influence of deformation on the crystallization rates [55,57]. For the range of cooling rates investigated, i.e.…”

Thermal and mechanical properties of stretched recyclable polyimide film

“…Cakmak and Kim 26 analyzed the molecular mechanism of necking for poly(etheretherketone) film, as well as the effects of polymer blend ratio on the maximum molecular arrangement. Kokturk et al 27 studied the effects of molecular structure and operating temperature on the film surface and the crystallization behavior of polylactic acid. El-Tonsy et al 28 examined the variation of CTE and the necking phenomenon of polypropylene during stretching.…”