Thermal annealing-induced superior toughness in polypropylene/poly(ethylene glycol) blend and its structural origin

Abstract

In this study, a water-soluble crystallizable polymer, poly(ethylene glycol) (PEG), was compounded with isotactic polypropylene (iPP), and a subsequent thermoannealing process was added to improve the toughness of iPP/PEG blend. By adding a small amount of PEG (5 wt%) into iPP, only a mild increment of 40% in toughness was achieved. However, the toughness of iPP/PEG (95/5) blend could be improved remarkably when the postprocessing procedure, thermal annealing, was utilized. For example, the notched impact strength of iPP/PEG blend annealed under 1208C for 12 h was five times of that of neat iPP. In addition, the tensile strength of annealed blend was slightly changed, compared with neat iPP. To ascertain the origin of toughening, various crystallographic and morphological/structural characterizations, including X-ray diffraction, electron microscopy, and calorimeter were employed. A specific structural change, in which more and more amounts of micrometer/sub-micrometer voids, yielded within the amorphous iPP region during the annealing process, was responsible for the prominent toughening behavior. FIG. 6. SEM images of crystal morphology of unannealed and annealed PP/PEG(95/5) blends: (a), (b) unannealed and (c), (d) annealed at 1208C.

Remarkably Improved Impact Fracture Toughness of Isotactic Polypropylene via Combining the Effects of Shear Layer-Spherulites Layer Alternated Structure and Thermal Annealing

“…Thermal annealing, between the glass transition temperature ( T g ) and melting temperature ( T m ), is one of the common and effective ways to improve mechanical properties of polymer. − Until now, a large quantity of work has been carried out to study the influence of annealing on the evolution of microstructure and mechanical properties of iPP. − It is widely accepted that the motion ability of molecular chain would be more active with increasing annealing temperature, which can significantly affect the development of microstructures and properties of iPP. Some researchers investigated the influence of thermal annealing on the adhesion of partial miscible blends …”

Crystallization behavior of polypropylene/silver nanocomposites using polyethylene glycol as reducing agent and interface modifier

“…The presence of PEG in PP, according to Li et al, improved the impact toughness and β-form content adding a small amount of PEG (5%) into iPP. 36 PP is a polyolefin with low adhesion due to its nonpolarity, and PEG is helpful in adhesion between the inorganic nanofiller and iPP matrix because the functional groups of PEG grafted into the PP have the function of interface between PP and Ag-NPs. PEG was used as a reducing agent and stabilizer of the Ag-NPs but also it can take the role of a modifier into the iPP.…”

“…Samples prepared by extruder process showed a lower K value (E-03/10 ¼ 12.6%, E-05/10 ¼ 17.6%, and E-10/10 ¼ 18.6%) due to a poor dispersion of the Ag-NPs. PEG remaining present in the structure of the compound according to Li et al 36 and addition of Ag-NPs can improve the crystallinity of iPP with the good dispersion of nanofiller by Brabender mixer because the amount of K is higher than other studies with Ag-NPs.…”