The new study, published in Cleaner Engineering and Technology, was conducted by Tomohiro Kono and Yasunori Kikuchi, who set out to close a persistent gap in the field of life cycle assessment. General industrial coatings form the second-largest segment of the global coating market, worth roughly 35 billion US dollars in 2019 and accounting for about 21 percent of total sales. Unlike automotive paint shops, which are typically operated by large corporations with dedicated environmental engineering teams, general industrial coating is dominated by small and medium-sized enterprises. These businesses vary widely in location, scale, and product type, which means their operating conditions differ enormously and standardized climate measures are difficult to implement. The researchers refer to this bundle of plant-specific attributes, from the size and weight of the coated object to the number of units processed per hour, as user-specific conditions.

Previous life cycle assessments of coating operations have tended to rely on measurements taken at particular plants or for particular coating systems. Such studies are valuable snapshots, but they cannot be transferred to a different factory with a different product, layout, or throughput. Mathematical models of individual process elements, such as oven energy consumption or film thickness in electrodeposition, do exist in transferable form, but none of them jointly produce the complete inventory of materials, waste, and energy needed for a proper life cycle assessment. The most integrated prior work, a life cycle assessment of three generic automotive coating systems, was not parameterized by user-specific conditions at all. The new model is designed to be the first formula-based tool that evaluates materials, waste, and energy across multiple coating systems while accepting user-specific conditions as direct inputs.

The model focuses on midcoat and topcoat processes and applies a common framework to three contrasting coating systems: solvent-based, water-based, and powder coatings. Each system imposes a distinct process configuration. Powder coating lines include powder recovery and recirculation loops and dispense with heated booth air, while water-based lines require preheating ovens and wet-type spray booths with extensive water management. The equations at the heart of the model combine standard physical principles, including mass and energy balances and stoichiometry, with parameters drawn from prior studies and interviews with industry practitioners. Paint consumption is derived from film thickness, film density, non-volatile matter content, and transfer efficiency, the fraction of sprayed paint that actually ends up as film on the object. Only powder systems, which collect and reuse oversprayed powder, achieve the high transfer efficiencies of around 80 percent; solvent- and water-based electrostatic spraying typically reaches about 50 percent.

The energy side of the model is where the physics becomes particularly detailed. Heat demand in the drying oven is decomposed into five components: heating the coated object and its carriers, heating the circulating air, evaporating paint media, warming the oven shell and insulation, and compensating for heat losses from the oven surface. The model also accounts for booth air heating when ambient temperatures drop below 298 kelvin, and for the behaviour of regenerative thermal oxidizers, the large combustion devices that destroy volatile organic compounds in exhaust gases. By balancing the combustion heat released by the solvents themselves against the heat required to raise incoming gas to combustion temperature, the model can determine whether an oxidizer is self-sustaining or needs supplementary fuel. Electricity consumption is similarly split into fan power, coating machine power, and oxidizer auxiliary power, each calculated from standard engineering relationships.

Running the model under standard operating conditions revealed stark differences between the three systems. Solvent- and water-based lines each consumed about 96 kilograms of paint-related inputs per hour, while the powder line needed only 35 kilograms thanks to its nearly solvent-free formulation and high transfer efficiency. Volatile organic compound emissions were dramatically different: 52 kilograms per hour for solvent-based, 13 for water-based, and a mere 0.0031 kilograms for powder. The thermal picture reversed the ranking. The powder system, which cures at high temperatures, demanded the most oven heat, while the solvent-based system demanded the least, with its oxidizer actually generating surplus heat from solvent self-combustion. The water-based system sat in between, with 60 percent higher oven heat demand than solvent-based owing to higher drying temperatures and a preheating stage.

When the inventories were translated into environmental impact scores using Japanese life cycle impact assessment methods and global warming potentials from the Intergovernmental Panel on Climate Change, the powder system emerged as the clear leader, showing the lowest values across most indicators. Water-based systems occupied an intermediate position, cutting life cycle greenhouse gas emissions by 11 percent relative to solvent-based coating. For photochemical oxidant formation, the smog-related impact dominated by volatile organic compounds, the water-based system reduced the burden by more than 70 percent and the powder system by essentially 100 percent compared with solvent-based coating. A partial validation against a real powder coating line showed the model predicting oven heat demand within 2 percent of measured values and fan electricity within 9 percent, encouraging evidence for a purely predictive tool.

Uncertainty analysis using Monte Carlo simulation with 10,000 iterations added important nuance. The 95 percent simulation intervals for powder coating did not overlap with either liquid system for global warming potential, confirming its advantage is robust. However, the intervals for solvent-based and water-based systems overlapped, meaning their relative ranking should be treated as marginal. Sensitivity analysis using Spearman rank correlations showed that the dominant levers differ fundamentally between systems. For solvent- and water-based coating, paint-related variables such as coated area, transfer efficiency, and film thickness mattered most, while for powder coating, drying temperature and oven size were the critical factors. In other words, the widespread habit of attacking drying energy first may be the wrong priority for liquid coating operations.

The model can also look forward. The researchers simulated next-generation scenarios, including a water-based paint that eliminates the preheating oven and raises transfer efficiency to 80 percent, and a powder paint that cures 45 kelvin lower at 150 degrees Celsius. The improved water-based scenario cut greenhouse gas emissions to 60 percent of the solvent-based baseline, with 24 points of that reduction coming from better transfer efficiency alone, and ended up essentially tied with the improved powder scenario. This suggests that factories currently committed to powder coating could switch to advanced water-based systems without sacrificing climate performance, provided cost and productivity requirements are met. Such evaluations, the authors note, can be performed before any capital is spent on new equipment or paint development.

The researchers are candid about limitations. The system boundary covers only midcoat and topcoat processes, excluding upstream pretreatment stages, plant construction, and the use and disposal of coated objects, so the ranking is conditional rather than a universal verdict. Validation covered only a single powder line, and the Monte Carlo analysis assumed independent input variables, a simplification that may widen the reported uncertainty ranges. Future work will extend the model toward cradle-to-grave assessment and develop a graphical user interface so field engineers can enter their own conditions directly. Even so, the study marks a meaningful shift for an industry long guided by rules of thumb: instead of guessing which coating system is greener, small and medium-sized manufacturers may soon be able to calculate it, tailored to the exact dimensions, throughput, and climate of their own shop floor.

Subject of Research: A predictive life cycle assessment model for comparing solvent-based, water-based, and powder industrial coating systems under user-specific operating conditions

Article Title: A predictive life cycle assessment model for comparing industrial coating systems under user-specific conditions

Article References: Kono, T., & Kikuchi, Y. (2026). A predictive life cycle assessment model for comparing industrial coating systems under user-specific conditions. Cleaner Engineering and Technology, 34, Article 101320. https://doi.org/10.1016/j.clet.2026.101320

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101320

Keywords: life cycle assessment, industrial coatings, volatile organic compounds, greenhouse gas emissions, powder coating, water-based coating, solvent-based coating, drying ovens, regenerative thermal oxidizer, Monte Carlo simulation, sustainability, manufacturing