Corona Decay Kinetics and Solventless Adhesive Wetting in Polypropylene Lamination
Corona decay on polypropylene impairs solventless adhesive wetting, requiring in-line treatment to maintain dynamic surface energy above 40 dyn/cm.
FTIR ATR Spectroscopy
Molecular Fingerprinting
Fourier transform infrared attenuated total reflection spectroscopy provides a nondestructive optical assay for identifying polymeric resins, additives, and surface contaminants on multilayer packaging films. The analytical technique relies on an internal reflection crystal with a high refractive index, which establishes an evanescent wave penetrating a shallow depth into the contacting substrate. Absorption bands within the mid infrared region generate a characteristic spectral profile that reveals molecular bonding arrangements.
Extrusion plants use this chemical profiling method to verify raw polymer grades before conversion and to detect surface migration of slip agents or plasticizers on extruded webs.
Surface Penetration
Penetration depth depends directly on the angle of incidence, the refractive indices of both the internal reflection element and the sample, and the specific wavelength of the infrared radiation. Zinc selenide and diamond prisms offer different mechanical durability and spectral transmission ranges, which dictates their selection for abrasive paper substrates or tacky barrier coatings. Contact pressure between the solid sample and the crystal face determines spectral repeatability, because air gaps attenuate the evanescent field and distort absorption band intensities.
Laboratory technicians correct baseline shifts and atmospheric interference mathematically before quantifying component ratios within multi-component adhesive laminates.
Quantitative Quality
Spectral library matching algorithms compare unknown sample spectra against verified reference databases to identify polymer contaminants or quantify copolymer ratios in biodegradable packaging films. Multivariate calibration models correlate specific peak height ratios with surface treatment levels, including corona discharge oxidation on polyethylene substrates intended for extrusion coating. Analytical variation remains below standard operational thresholds when sample preparation follows strict cleaning protocols for the internal reflection crystal between successive measurements.
Finished roll acceptance relies on these reproducible absorbance values to confirm compliance with chemical migration limits set for food contact packaging applications.