Hot-air welding could make it easier to build structures from recyclable composite materials in the field. Researchers at Skoltech in Moscow have shown that thermoplastic composite profiles can be joined with hot air to a strength comparable with more complex welding methods. A Skoltech release by Nicolas Posunko, carried by TechXplore on 22 October 2026, describes the work. The underlying paper, “Hot-gas welding of thermoplastic pultruded profiles”, was published in the Journal of Materials Research and Technology on 23 September 2026. This article is based on that release and paper.
What is being welded
The material is a thermoplastic pultruded profile made of glass fibre and polypropylene. Pultrusion is a process that pulls fibres through a resin to form long, continuous shapes such as beams and rods. Unlike metal, these profiles do not rust. Unlike many traditional composites, which use resins that cannot be remelted, thermoplastic composites can be softened by heat, which means they can be welded and recycled.
The team says the approach could help build and maintain bridges, cell towers, warehouses and other infrastructure using inexpensive, portable equipment, especially in remote areas. Today, according to Safonov, structures such as wind turbine and transmission towers and pedestrian overpasses are built from concrete and metal, which rusts, or from thermoset polymers, which cannot be recycled and must be joined with bolts, rivets or adhesives.
How hot-air welding was tested
The researchers looked at four process parameters: heating time, air temperature, pressure and how long the pressure is applied. Using a statistical method known as Taguchi design, combined with analysis of variance (ANOVA), they measured how much each factor affected the strength of the weld.
The results were lopsided. Heating time accounted for 76.9% of the effect on weld strength. Air temperature accounted for 16.4%, pressure for 6.0% and pressure duration for just 0.7%. In other words, getting the heating time right matters far more than anything else.
How strong the hot-air welding joints are
The best joints reached a strength of 8.95 ± 0.56 MPa, with a coefficient of variation of 6.2%, which indicates fairly consistent results. According to the researchers, this is comparable with ultrasonic and resistance welding and “not critically inferior” to induction welding. Those methods all need more complex equipment.
When the joints did fail, the failure happened within the laminate itself rather than at the weld line, and there were no unbonded areas. That suggests the weld was not the weakest point.
From lab press to field tools
In the lab, the team used a press to apply pressure. In the field, they suggest the same job could be done with hydraulics similar to a scissor jack and a portable heat gun. That is the main appeal: welding that could be done on site with simple, portable tools.
The paper’s authors are Nikita Lyashenko, Sergey Gusev and Alexander Safonov, an associate professor at Skoltech Materials and the project’s principal investigator. For another materials story, see our report on WPI’s upcycled battery materials.
The case for and against
The case for this work is practical. Rust-free, recyclable profiles that can be joined with a heat gun and simple hydraulics could suit places where heavy welding equipment is hard to bring in. Knowing that heating time dominates also gives workers a clear parameter to control.
The case for caution is that these are laboratory tests. Field conditions such as wind, cold and uneven surfaces could affect heating, and the release does not report long-term durability or full-scale structural tests. The paper itself dates from September.
My view on hot-air welding
As a writer, I feel this is a nice example of research that aims at simplicity rather than complexity. A portable heat gun is about as low-tech as tools get, and if it really produces joints close to those from ultrasonic or induction welding, that could lower costs for building in remote places. I would want to see a full structure built and tested outdoors before drawing big conclusions.
FAQ: Skoltech hot-air welding
What did Skoltech weld with hot air?
Glass fibre and polypropylene thermoplastic pultruded profiles, which are rust-resistant and recyclable.
Which factor matters most for hot-air welding strength?
Heating time, which accounted for 76.9% of the effect on weld strength, far ahead of air temperature at 16.4%.
How strong were the welds?
About 8.95 MPa, comparable with ultrasonic and resistance welding, according to the researchers.