These emerging materials represent distinct opportunities for more sustainable product and process designs. As we have seen, some promising materials might be promoted as green or environmentally friendly, but in many instances it is not entirely clear if these materials represent a more sustainable alternative to the traditional materials. For a complete sustainability assessment of new materials, it is necessary to obtain a comprehensive data set for hazard identification, impact assessment, and mitigation. It is necessary for these assessments to be conducted from a life cycle perspective so that the broader implications of new materials are included. Innovation is one of the main drivers for sustainability and cannot be discouraged. At the same time, this innovation needs to be framed by the tenants of sustainability, green chemistry, and green technology, so that the development of new materials accounts for their potential impacts to humans, other species, and the environment.
In Chapter 22 we explore in greater detail the advantages, impacts, needs, and uncertainties of a big sector related to some of the materials we have explored in this chapter: renewable materials.
PROBLEMS
21.1 One potential application for nanoparticles in the electronic manufacturing indus- try is their use in specialty polishing operations, such as chemical–mechanical planarization (CMP), which is critical to semiconductor and chip manufacture.
CMP relies on a slurry of oxide nanoparticles for both chemical reaction and mechanical abrasion between the slurry and the film to obtain smooth and flat silicon wafers. CMP is also used to polish magnetic hard disks. What are the disadvantages and advantages of CMP from a green engineering/green chemistry perspective?
21.2 Some microorganisms have been found to produce nanoparticles. For example, bacterial proteins have been used to produce magnetite in laboratories, yeast cells can
create cadmium sulfide nanoparticles, and gold and silver nanoparticles have been obtained from fungus and viral proteins, respectively. What are the advantages and disadvantages of these potential future methods of producing nanoparticles from a green chemistry/green engineering perspective?
21.3 Carbon nanotubes (CNTs) have potential uses in a wide range of applications (e.g., composite materials, batteries, memory devices, electronic displays, transparent conductors, sensors, medical imaging). However, some scientists have expressed concerns regarding the effects of some CNTs. What are those concerns?
21.4 In Section 21.3 it was noted that applications for PTT are being developed mainly in the fibers and films sectors. What specific commercial applications would this mean for the public?
21.5 Bohlmann performed a streamlined LCA comparison of PLA vs. PP yogurt contain- ers using energy as a surrogate for environmental impact. The results he obtained are given in Table P21.5A.
(a) What conclusions can you draw from the results?
(b) Bohlmann also prepared a sensitivity assessment on the energy production for lactic acid, accounting for the base case (using triple-effect evaporators in the calculations) and the worst case (double-effect evaporators) (Table P21.5B).19 What additional conclusions can you draw from the sensitivity assessment?
21.6 A cradle-to-grave LCA of a few poly(3-hydroxybutyrate) (PHB)-based composites was performed for comparison with petrochemically derived polymers used in cathode-ray tube (CRT) monitor housings [produced conventionally from high-
TABLE P21.5A Bohlmann’s Results
Energy Category PLA PP
Fuel production (MJ/kg) 3.9 6.6
Fuel use (MJ/kg) 47.5 30.8
Transportation (MJ/kg) 4.7 4.8
Feedstock (MJ/kg) 0.6 51.5
Total (MJ/kg) 56.7 93.7
Total (MJ/ton yogurt) 2225 3261
TABLE P21.5B Bohlmann’s Best and Worst Case Analysis
Gross Energy Base Case Worst Case
Energy for lactic acid production (MJ/kg) 30.4 44.1
Total energy for PLA (MJ/kg) 56.7 75.3
impact polystyrene (HIPS)] and internal automotive panels [normally produced from glass-fiber-filled polypropylene (PP-GF)] (Figure P21.6). What conclusions can you draw from the data?
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0 1 2 3 4 5 6 7 8 9
PP PHB-4
PHB-3 PHB-2
PHB-1
0 20 40 60 80 100 120 140 160 180 200
PHB-4 PHB-3
PHB-2 PHB-1
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Nonrenewable energy (MJ/functional unit) GWP (kg CO2-eq/functional unit)
(b) (a)
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