Plastic bonding enhancement

Learned something interesting last night at a makerspace while talking to the 3D printer guys about adhesives used with ABS and PLA, the two plastics most used with 3D printers. One of them mentioned the enhancement of bonding using a quick pass of the plastic's mating surface through a torch flame. Looked it up and found this:

https://www.specialchem4adhesives.c...ndex.aspx?id=surfacetreatment&idmenu=factors3

Flame Treatment

Flame treatment increases the bondability of a plastic by oxidizing the surface through brief exposure to flame. The oxidation proceeds by a free radical mechanism, accompanied by chain scissions and some crosslinking. The functionalities introduced by oxidation are hydroxyl, carbonyl, carboxyl, and amide groups with a typical oxidation depth of approximately 4 to 9 nanometers. The improved bondability results from increased wettability, due to increased surface energy, and interfacial diffusivity, caused by chain scissions.

Common uses polyolefins, polyacetals, polyethylene, terephthalate

Iodine Treatment

Iodine treatment increases the bond strengths achieved on a substrate by altering the surface crystallinity from alpha form (where the N-H groups lie parallel to the surface) to beta form (where the N-H groups stand perpendicular to the surface). The surface remains relatively smooth after treatment, so it is believed that increased chemical reactivity, rather than mechanical interlocking is the mechanism for improved adhesion.

Common uses nylon

More:

https://www.adhesives.org/docs/default-document-library/surfaceprep_adhesives-org.pdf?sfvrsn=0

Excerpt:

Flame treatment of the substrate surface for just a few seconds with an oxygen-containing (blue) propane or acetylene gas flame leads to the incorporation of oxygen-containing groups at the surface. This improves the wetting properties and hence the adhesion. Flame treatment is used almost exclusively for polyethylene and polypropylene substrates. The effect of the pretreatment subsides within a short time so that flame-treated substrates must be bonded immediately.

EDIT - More:

https://www.henkelna.com/us/content_data/Hard_to_Bond_Plastics756739.pdf

In flame treatment, various reactive groups such as hydroxyls, carbonyls and carboxyls are introduced to bonding surfaces through an oxidation reaction when the substrate is exposed to flame. In addition, flame treatment lowers the surface energy of the substrate surface, allowing for better wetting. Flame treatment is commonly used on polyolefins and polyacetals, and is most frequently used when bonding with cyanoacrylate adhesives.