Stage-based Sustainability Assessment

In this work, an examples of automotive nanocoating materials was selected. This coating materials for automotive clearcoat was a solventborne paint system while the additive nanoparticle is nano-silica (20nm). The quantities of raw materials given in Table 2.11 are in weight percent of the total paint weight.

Category Indicator

Economic

sustainability E1 Cost of energy consumption per vehicle during disposal

Environmental sustainability

V1 Energy consumption per vehicle used during disposal V2 Percentage of material recycled

V3 The quantity of waste generated during disposal V4 The quantity of nanoparticle released during disposal Social

Table 2.11. Automotive nanocoating formulation. Material Quantity (w.t. %) Naptha 3 Xylene 16 Methanol 2 Melamine formaldehyde 11 Ethylbenzene 1 N-butyl alcohol 11 Cumene 1 MTS* 5 Butyl acetate 3 PMMA* 40 Silicon dioxide (20nm) 6

* MTS: 3-methacryloxypropyl-trimethoxy-silane; PMMA: Polymethylmethacrylate For the stage 1-paint manufacturing process, the selected plant has an annual production capacity of 2.54 ×107 _{kg for this nanocoating material and the total annual}

material cost is $ 1.2 ×108. Annual energy consumption for the production plant is 1.5×108 kWh and the cost is equivalent to $ 1.65 ×107. Annual VOC consumption is 1.27×107 kg for this specific paint material. About 5% of total nanomaterials is released to the manufacturing environment which leads to a very high health impact and low safety rating. Based on the feedback from downstream customer, the satisfaction of paint quality is rated as high.

The fact of coating manufacturing system can then be converted to the sustainability status based on the defined sustainability metrics system for stage 1 based on Eqs. (2.7)- (2.9). The result of sustainability assessment is shown in Table 2.12. The actual sustainability performance is normalized based on the current best and worst industrial practice. In this

case, all of the weighting factors are considered equally important and set to 1. Therefore, the economic, environmental, social and overall sustainability status can be obtained as 0.49, 0.42, 0.39, and 0.44, respectively by following Eqs. (2.10)-(2.13).

Table 2.12. Sustainability assessment of life cycle stage 1.

Category Indicator Current status Normalized value Worst Best Economic sustainability E1 ($/kg) 4.72 0.48 6.5 2.8 E2 ($/kg) 0.65 0.50 0.9 0.4 Environmental sustainability V1 (kWh/kg) 5.9 0.50 8.3 3.5 V2(kg/kg) 0.5 0.71 0.75 0.4 V3 (%) 5 0.17 6 0 V4 0.7 0.30 1 0 Social sustainability L1 0.75 0.50 0.5 1 L2 0.35 0.28 0.1 1

The evaluation of stage 2 - coating spray process is based on the results of computational modeling (Uttarwar and Huang, 2013). The selected nanocoating spray process has the same design as traditional spray booth and a center spray pattern is applied to the spray robotic nuzzle. Given that the production line has an annual production capacity of 4.1×104 vehicles, the annual energy consumption due to paint spray and air ventilation in the spray process is 2.1×106 kWh and the cost is equivalent to $ 2.2 ×105. During spray, the concentration of nanoparticles in booth air is 2.3×1012 _{per m}3_{. An estimated 25% paint}

material is carried out to the sludge by down drafting air. 2% total amount of nanoparticles will be released to the environment. VOC emission is 1.3 kg for each spray job. The average

film thickness when coating is partially wet is 29.7 μm and the film surface topology is rated as average based on expert’s knowledge.

Such information can be used to evaluate the status of selected sustainability indicators. Table 2.13 describes the result of sustainability assessment. The actual sustainability performance is normalized based on the current best and worst industrial practice. By applying Eqs. (2.10)-(2.13), the economic, environmental, social and overall sustainability status can be obtained as 0.55, 0.53, 0.59, and 0.56, respectively.

Table 2.13. Sustainability assessment of life cycle stage 2.

Category Indicator Current status Normalized value Worst Best Economic sustainability E1 (%) 75 57 55 90 E2 ($/vehicle) 5.4 0.54 6.1 4.8 Environmenta l sustainability V1 (kWh/vehicle) 49.1 0.54 55.5 43.6 V2 (kg/vehicle) 0.9 0.60 1.5 1 V3 (×1012 per m3) 2.3 0.38 3.7 0 V4 (%) 2 0.60 5 0 Social sustainability L1 0.7 0.63 0.2 1 L2 0.6 0.56 0.1 1

The evaluation of stage 3 - coating curing process is obtained from multiscale computational modeling (Song et al., 2016). It is expected that the curing oven setting follows the one for conventional clearcoat baking process. Thus, the heating source for the selected nanocoating curing process consists of radiation and convection air heating. Given that the production line has an annual production capacity of 4.1×104 _{vehicles, the annual}

energy consumption due to in the curing process is 2.87×106 kWh and the cost is equivalent to $ 3.15×105_{. It is expected that 1% total amount of nanoparticles in the wet film will be}

released to the environment. The conversion rate of cross-linking reaction in the coating film could reach 90%. In the meanwhile, coating mechanical performance could improve 40% over conventional clearcoat after curing and the coating thickness might be 2 μm thicker than what is expected due to the solvent residual remaining in the film.

Such information can be used to evaluate the status of selected sustainability indicators. Table 2.14 describes the result of sustainability assessment. The actual sustainability performance is normalized based on the current best and worst industrial practice. By applying Eqs. (2.10)-(2.13), the economic, environmental, social and overall sustainability status can be obtained as 0.83, 0.71, 0.56, and 0.71, respectively.

Table 2.14 Sustainability assessment of life cycle stage 3.

Category Indicator Current status Normalized value Worst Best Economic sustainability E1 ($/vehicle) 7.7 0.83 9.35 7.35 Environmental sustainability V1(kWh/vehicle) 70 0.75 85 65 V2 0.01 0.67 0.03 0 Social sustainability L1 1.4 0.57 1 1.7 L2 0.9 0.55 0.85 0.94

Note that this study is only for demonstrative purpose of the proposed LCBSA framework. To simplify the case study, stage 4 (use and maintenance) and stage 5 (end of life) are not studied in this work due to the insufficient knowledge about the coating performance in the long-term and disposal techniques.