Abstract
This study reports on the use of poly(lactic acid) (PLA) as a renewable thermoplastic adhesive for laminated panels using birch, spruce, and pine veneers. Consolidated panels were prepared from veneer and PLA foils by hot-pressing from 140 to 180 °C to achieve minimum bondline temperatures. Evaluation of panel properties revealed that the PLA-bonded panels met minimum tensile strength and internal bond strength performance criteria. However, the adhesion interface which developed within individual bondlines varied with distinctions between hardwood and softwood species and PLA grades. Birch samples developed greater bondline strength with a higher pressing temperature using semi-crystalline PLA, whereas higher temperatures produced a poorer performance with the use of amorphous PLA. Panels formed with spruce or pine veneers had lower bondline performance and were also similarly distinguished by their pressing temperature and PLA grade. Furthermore, the potential for PLA-bonded laminated panels was demonstrated by cold water soak testing. Samples exhibiting relatively greater bondline adhesion had wet tensile strength values comparable to those tested in dry state. Our study outcomes suggest the potential for PLA bonding of veneers and panel overlays with the added benefits of being renewable and a no added formaldehyde system.
Highlights
The momentum for change toward sustainable, renewable, and recyclable products is growing rapidly across many industrial and market sectors
The veneers were equilibrated by conditioning at a temperature of 20 ◦ C and 30% relative humidity (RH)
A relatively higher tensile strength achieved with 0.5 mm poly(lactic acid) (PLA) foil for amorphous PLA-birch samples (Table 3) was likely due to greater PLA retained at the PLA-wood interface than achieved with the use of 0.3 mm foil
Summary
The momentum for change toward sustainable, renewable, and recyclable products is growing rapidly across many industrial and market sectors. This desire transcends the packaging and composite sectors where environmental indices, recyclability, and legislative regulations are the principal drivers for change [1,2]. While formaldehyde use and emissions have featured prominently in these developments, the substitution of petrochemical components in wood binders is topical. Such activities are creating opportunities for new adhesives and approaches to bonding wood along with adaptations to more traditional approaches. The use of polyolefin plastics with wood fiber has been an active research area including commercial applications as wood plastic composite (WPC) materials [7,8] and examples of Fibers 2020, 8, 50; doi:10.3390/fib8080050 www.mdpi.com/journal/fibers
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