Blown Composite Films of Low-Density/Linear-Low-Density Polyethylene and Silica Aerogel for Transparent Heat Retention Films and Influence of Silica Aerogel on Biaxial Properties

Abstract

Blown films based on low-density polyethylene (LDPE)/linear low-density polyethylene (LLDPE) and silica aerogel (SA; 0, 0.5, 1, and 1.5 wt.%) were obtained at the pilot scale. Good particle dispersion and distribution were achieved without thermo oxidative degradation. The effects of different SA contents (0.5–1.5 wt.%) were studied to prepare transparent-heat-retention LDPE/LLDPE films with improved material properties, while maintaining the optical performance. The optical characteristics of the composite films were analyzed using methods such as ultraviolet–visible spectroscopy and electron microscopy. Their mechanical characteristics were examined along the machine and transverse directions (MD and TD, respectively). The MD film performance was better, and the 0.5% composition exhibited the highest stress at break. The crystallization kinetics of the LDPE/LLDPE blends and their composites containing different SA loadings were investigated using differential scanning calorimetry, which revealed that the crystallinity of LDPE/LLDPE was increased by 0.5 wt.% of well-dispersed SA acting as a nucleating agent and decreased by agglomerated SA (1–1.5 wt.%). The LDPE/LLDPE/SA (0.5–1.5 wt.%) films exhibited improved infrared retention without compromising the visible light transmission, proving the potential of this method for producing next-generation heat retention films. Moreover, these films were biaxially drawn at 13.72 MPa, and the introduction of SA resulted in lower draw ratios in both the MD and TD. Most of the results were explained in terms of changes in the biaxial crystallization caused by the process or the influence of particles on the process after a systematic experimental investigation. The issues were strongly related to the development of blown nanocomposites films as materials for the packaging industry.

Preparation and Characterization of Thermal-Insulating Microporous Breathable Al/LLDPE/CaCO3 Composite Films

“…Figure 8 b shows that, similar to the MD sample ( Figure 8 a), the stress-at-break value of the Al (2–8 wt.%)/LLDPE/CaCO 3 composite films slightly increases and the Al (8 wt.%)/LLDPE/CaCO 3 composite film exhibits the highest stress-at-break (2.67 MPa). In this case, the improvement in the tensile properties can be explained by considering the probable influence of Al on the molecular orientation during the film extrusion, along with the good matrix–particle adhesion [ 32 ].…”

“…According to Figure 8a, the stress-at-break value of the LLDPE/CaCO3 composite film increases after incorporating Al (2-8 wt.%), and the composite with 8 wt.% of Al loading shows the highest stress-at-break (10.41 MPa). In this instance, the improvement in the tensile properties can be explained by considering the potential impact of Al on the molecular orientation during the extrusion along the MD, as well as the strong matrix-particle adhesion [32], therefore promoting the increase in the tensile strength of the composite film with the incorporation of the Al particles (2-8 wt.%). On the other hand, the stress-strain curves demonstrated that the strain-at-break value of the LLDPE/CaCO3 film increases from 76.15% to 138.03% with the incorporation of Al (2-8 wt.%).…”