On a trip to a timber conference recently I stumbled upon a Christmas market, which set me musing about the steady rise in laser grade sheet materials. Once the preserve of makers and enthusiasts, these days the hobby sector is booming with laser cut shapes available for all seasons in craft shops and mainstream home décor stores.
No sooner have the pumpkins been sold than the reindeer and snowflakes emerge, soon to be followed by pastel coloured rabbits and eggs then onto summer holiday symbols… you name it, there will be someone somewhere willing to laser cut some plywood or MDF and sell it!
So with all that said, lets focus in on the wood panels themselves. Many laser cutters require the user to be selective about the type of panel they choose to cut or engrave. Certain grades of MDF and plywood are favoured for their uniformity through the thickness (low incidence of voids or gaps that would lead to rough-looking edges in the finished product). Birch ply was at one time the staple, but supplies have decreased due to the ongoing situation in Russia and Ukraine, so poplar has been a stand in, but tropical species can also give good results – Ceiba pentandra is one example, with a good texture. Oak can be used for its more coarse textured grain – but only when this is a design feature for the surface. In fact, oak veneer on MDF might be chosen to avoid the large pores showing on edge sections.
All of this has ignored the largest issue, which is the adhesive used in the panel. Some website guidance for hobbyists recommends avoiding melamine glues or phenolic glues due to the likelihood of unpleasant chemicals or formaldehyde in the gas emitted during laser cutting. Other websites say the opposite – suggesting melamine glue is favoured as it tends to burn cleanly and vaporize rather than smoke when laser cut. How can we know which advice to follow? Other guidance indicates that panels marked as E0 would be ok, as they have low formaldehyde content. This is a different question – grades like E0, E1 etc relate to measured free formaldehyde (emitted by the panel during normal ambient conditions) – not to the decomposition during laser cutting. It relates to tests done by the chamber method, and can be measured for any formaldehyde-based resin.
So, what is really happening when the laser cutter works on the panel? The laser energy rapidly heats the wood. Certain lasers are very effective on the wood molecules, for example a CO2 laser has a wavelength of 10.6μm (in the infrared range) rapidly providing energy to the wood, creating the plasma plume during cut or hole formation.
The plasma that forms contains fragments of the wood molecules, and the adhesive molecules from the panel (which can include formaldehyde and depending on the resin perhaps also phenol). Most of the wood substance rapidly converts into CO2 and water however some fragments are larger, and can include alkanes, phenolics and benzene. From the adhesive there might be formaldehyde and other monomers.
At the edges of the laser cut some of this material re-deposits as a char type residue, giving the dark brown sometimes seen on the cut edge or the engraved pattern. Energy received by the wood can be altered by the user adjusting the power, speed and optics to encourage formation of this char to produce the etched patterns, or to reduce char formation and increase cut efficiency.
A lot of website advice skips over the other aspect, the particles produced during laser processing predominantly have an aerodynamic diameter of less than 0.1 (known as ultrafine particles) which can also pose health risks. So it seems that good ventilation and filtration would be advisable regardless of the glue type used in the panel! Being selective about the glue type is certainly good advice but extraction systems need to be considered for industrial usage, so make good sense for many hobby users as well.
