Effects of the biaxial orientation on the mechanical and optical properties and shrinkage of polyamide 6‐66–montmorillonite–nanosilica nanocomposite films

Abstract

Polyamide 6-66 (PA6-66)-montmorillonite (MMT)-nanosilica (NS) nanocomposite films were fabricated through a cast film process and then biaxially stretched on a laboratory stretcher. Uniaxial or biaxial stretching induced the elongated conformation of MMT and NS. The b axis of the α crystals and the amorphous phase were revealed to align along the machine direction (MD) after stretching, with the uniaxial orientation playing a more significant role. Furthermore, the crystallinity of PA6-66 stretching increased with the stretching ratio. Uniaxial stretching gave rise to a significantly enhanced tensile strength along the MD, whereas it slightly decreased the mechanical properties along the transverse direction (TD). In contrast, the films subjected to biaxial stretching exhibited more balanced mechanical properties. Uniaxial and biaxial stretching led to decreased transmittance and increased haze in the PA6-66-MMT-NS films; this could have been due to the elongated nanostructure of the two nanofillers, which inhibited the transmission and facilitated the scattering of visible light. The thermal shrinkage of the films increased with increasing stretching ratio, and the biaxially oriented films presented nearly equal shrinkage in the MD and TD. The addition of nanofillers decreased the shrinkage attributed to the mobility inhibition of the polymer chains during heating.

Structural evolution and properties of polyamide‐6/poly(ether block amide) films during the simultaneous biaxial stretching

“…This phenomenon could be attributed to the increase of molecule chain orientation in amorphous regions, which would try to retract back to their original state and form the most random conformation when heated, resulting in the occurrences of shrinkage. Similar behavior was found by Liu et al 35 in the study of PA-6-66/ montmorillonite/nanosilica nanocomposite films.…”

Biaxial Stretching of Polymer Nanocomposites: A Mini-Review

“…From Table 2, for the uniaxially stretched films, the tensile strength in the stretching direction gradually increased with increasing SR, and the biaxially stretched nanocomposite films showed more balanced mechanical properties and thermal shrinkage along the machine direction and transverse direction compared with the uniaxially stretched composite (Liu et al, 2019).…”

Poly(vinyl alcohol)/Kaolin Barrier Films with Superior Dispersion Fabricated by Solid-State Shear Milling and Biaxial Stretching

“…Apparently, with the help of biaxial stretching, both the strength and modulus of the stretched films were dramatically improved owing to the in-plane orientation of microstructures (Figure 6d,e). For example, unstretched PVA/K5 exhibited a tensile strength of 25.7 MPa and a modulus of 29.3 MPa, while for BO-PVA/K5, its tensile strength reached 146.4 MPa with a Young's modulus of 5.5 GPa, even beyond some engineering plastics such as nylon, 36,37 fully meeting the requirements of high-performance packaging materials for mechanical properties. It was worth noting that the superdispersed kaolin reduced the interaction between PVA molecules to some degree because of its physical blocking effect, resulting in the decrease of the elongation at break.…”