Analysis of coextruded polyethylene-based packaging films: number of layers, composition, and mechanical properties

• Published in: Polymer bulletin (Berlin, Germany) Vol. 78; no. 4; pp. 1981 - 1996
• Main Authors: Balkova, Radka, Kucera, Frantisek, Jancar, Josef
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-04-2021; Springer Nature B.V
• Subjects: Additives; Calcite; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Coextrusion; Complex Fluids and Microfluidics; Composition; Cooling; Copolymers; Crystallization; Density; Differential scanning calorimetry; Ethylene vinyl acetates; Flexible packaging; Fourier transforms; Fracture surfaces; Glass substrates; Heat; Infrared spectroscopy; Low density polyethylenes; Mechanical properties; Microscopy; Molecular weight; Nitrogen; Organic Chemistry; Original Paper; Packaging; Physical Chemistry; Polyethylene; Polyethylenes; Polymer blends; Polymer Sciences; Quality control; Scanning microscopy; Soft and Granular Matter; Spectrum analysis; Surface layers; Temperature; Thermogravimetry; Thickness; Thin films; X-ray diffraction; Number and thickness of layers; Coextruded film; Polyethylene types; Isothermal crystallization; Confocal laser scanning microscopy
• ISSN: 0170-0839; 1436-2449
• DOI: 10.1007/s00289-020-03196-2

Five coextruded and one blown polyethylene (PE)-based packaging films were analyzed with the aim to determine the number and thickness of the film layers and tensile mechanical properties and to prove composition declared by a producer. They were chosen the most effective methods such as Fourier-transform infrared spectroscopy (attenuated total reflectance and transmission modes), differential scanning calorimetry (DSC), thermogravimetry, wide-angle X-ray diffraction (XRD), and confocal laser scanning microscopy. The latter turned out to be very effective method to show the film layers on its fracture surfaces due to very good contrast and different fracture patterns of each layer. Two to five layers were detected in the films, whereas silicone surface layer with the thickness not higher than 1 µm was very nicely detected in two coextruded films. The type of PE (low density, linear low density and high density) was determined by DSC, whereas miscible types of PE were differentiated only after performance of stepwise isothermal crystallization. This was performed in case of four films at 124, 114, 104, and 94 °C with 30-min dwell at each temperature. Random copolymer of polypropylene was identified by DSC in two films. Infrared spectroscopy revealed polymers present in low content (ethylene–vinyl acetate and silicon) and, in addition, additives such as calcite, which was detected also by XRD. The major polymer components were proved in four films. Mechanical properties varied in machine and transverse direction in case of all films. The methods used are also recommended for quality control of coextruded films.