PLA wear layer based luxury vinyl tiles - Construction and characterization for adhesion strength and wear vs PVC

Abstract

Polylactic acid (PLA) bio-renewable green polymer films were studied for their use as a drop-in alternate to polyvinyl chloride (PVC) films as the top surface wear layer wear layer for luxury vinyl tiles (LVT). The wear layer is to be adhesively bonded under heat and pressure to an underlying composite layer comprising a thin ∼0.08 mm oily print layer (PL) bonded onto a relatively thick ∼2.5 mm ethyl vinyl acetate (EVA) backing layer (BL). The relative effects of PLA sheet thickness and surface adhesion properties under heat and pressure over time were studied for their influence on key metrics pertaining to tensile strength, elongation at failure, peel strength, wear layer abrasion, and LVT thickness reduction (correlated to print design distortion). Studies were complemented with differential scanning calorimetry (DSC) and PLA surface pretreatments involving Corona plasma discharge, silicone layer coating, and surface roughening. Optimal processing parameters resulted in distortion-free PLA-LVTs (in sizes ranging from 0.1 m × 0.1 m to 0.3 m × 0.3 m) with adhesion peel strengths 1.5–2.1 N/mm (9–12 pli), and wear layer abrasion resistance >2000–4000 taber cycles. This was achieved using 300–500 μm thick crystalline PLA films compressed onto PL-BL composite layers, with platens heated between a narrow range of 90.5–93 °C, under 1 MPa compression, and applied for ∼5–10 min. The onset of unacceptable distortion (>0.2 mm thickness reduction) occurs at/beyond ∼ 95 °C which correlates with onset of melting of the PL coupled with accelerated plastic deformation for the already melting EVA base layer. Effects of PLA wear layer surface pre-treatment reveal that silicone layer did not lead to noticeable changes in peel strength when using a single PLA wear layer. However, close to 100% increase peel strength was noted for PLA-LVTs using a double lap layer of non-silicone coated PLA films. Corona plasma discharge and surface roughened PLA wear layer surprisingly resulted in a significant (∼90%) degradation of peel strength. Related analyses on competing effects and/or influences of above-mentioned key parameters are discussed.