15 Biobased Thermosets Ana Dotan Pernick Faculty of Engineering, Shenkar College of Engineering and Design, Ramat-Gan, Israel OUTLINE Polymers from Renewable Sources 577 Thermoset from Renewable Sources 594 Determination of Bio-Based Content in References 615 Polymers 578 Raw Materials for Renewable Sources Polymers 579 Polymers from Renewable Bio-based polymers are derived from renewable Sources resources such as plant and animal mass from CO2 recently fixed via photosynthesis [2]. Bio-based poly- In the past few decades concern about the environ- mers can be natural or synthetic. Natural bio-based ment, climate changes, and limited fossil resources polymers are polymers synthesized by living organ- has led to an intensive research of alternatives to isms such as animals, plants, algae, and microorgan- fossil-based polymers. From a historical point of isms. The most abundant bio-based polymers in view, the first polymers used by mankind were from nature are polysaccharides [3]. Cellulose and starch renewable sources, bio-based polymers, long before are natural polymers based on polysaccharides, and the birth of synthetic polymers. Celluloid, a bio- are abundant in nature. Proteins and bacterial polyhy- based man-made polymer was invented in the 1860s, droxyalkanoates are also natural bio-based polymers and since then, many other bio-based polymers have [4]. Bio-based polymers are not necessarily sustain- been developed. However, the development of the able; this depends on a variety of issues, including crude oil industry in the 20th century transformed the the source material, production process, and how the world of polymers, leading to the use of synthetic material is managed at the end of its useful life. Sus- polymers as a replacement for bio-based polymers. tainable produced bio-based polymers are those The increasing use of synthetic polymers as a result grown without genetically modified organisms of the growing human population and standard of liv- (GMOs), hazardous pesticides, certified as sustain- ing in the next decades will result in higher demands able for the soil and ecosystems, and compostable. on oil production and will contribute to a possible Sustainability also depends on the reduction of depletion of crude oil before the end of the 21st cen- impacts to occupational and public health as well as tury. It is estimated that by 2015 the worldwide the environment throughout their life cycles [2].Bio- annual production of plastics is very likely to reach based materials are important candidates for sustain- 300 million tons (14À18% are thermosets), which able development since they present the potential to will require large amounts of petroleum and will reduce greenhouse emissions by sequestering CO2,to result in the emissions of hundreds of millions of tons reduce raw material costs, and to create opportunities of CO2 to the atmosphere [1]. A return to bio-based for growth and employment in agriculture [5]. polymers will reduce the dependency of the polymers Life cycle assessment (LCA) is the most widely and plastics industry on petroleum, thus creating applied and accepted method to quantitatively assess more sustainable alternatives. the environmental impact of a given material Handbook of Thermoset Plastics. DOI: http://dx.doi.org/10.1016/B978-1-4557-3107-7.00015-4 © 2014 Elsevier Inc. All rights reserved. 577 578 HANDBOOK OF THERMOSET PLASTICS throughout its life cycle; its principles and frame- carbon dating), because ancient petroleum has lost work are described in ISO 14040 [6]. Usually the its 14C through radioactive decay whereas feedstock impact categories considered in LCA are global derived from recently living organisms have a 14C warming, acidification of soil, ozone layer depletion, content related to the current equilibrium concen- aquatic eutrophication, respiratory organics, respira- tration in the atmosphere. tory inorganics, land occupation, non-renewable ASTM D6866-11 has developed a protocol to energy, and aquatic ecotoxicity [7]. Additional envi- quantify the bio-based content in materials by com- ronmental indicators are resource depletion and paring the 14C/12C ratio to that of a standard speci- human toxicity [5]. men typical of living organisms [11]. CEN/TS Global warming impact is measured by the 16137 is the equivalent European for the ASTM amount of CO2 that is liberated from the material standard test [3]. ASTM D6866-11 is the Standard throughout its life cycle. CO2 is the principal anthro- Test Methods for Determining the Bio-based pogenic gas that is thought to affect the Earth’s radia- Content of Solid, Liquid, and Gaseous Samples tive balance. For this reason it is believed that there Using Radiocarbon Analysis. It defines bio-based is a close correlation between CO2 and the change of content as the amount of bio-based carbon in the the Earth’s temperature [8].TheCO2 footprint of a material or product as a percent of the weight material is assessed by the carbon emissions conse- (mass) of the total organic carbon in the product. quent on the creation of a unit mass of material, This standard utilizes two methods to quantify the including those associated with transport, generation bio-based content of a given product: (a) Accelera- of the electric power used by the plant, and that of tor Mass Spectrometry (AMS) along with Isotope feedstocks and hydrocarbon fuels. The CO2 footprint, Ratio Mass Spectrometry (IRMS); or (b) Liquid which is measured in units of kg of CO2/kg material, Scintillation Counters (LSC) using sample carbon is the sum of all contributions per unit mass of mate- that has been converted to benzene. Those methods rial. Renewable resource polymers have a low CO2 directly discriminate between product carbon result- footprint since plants grow by absorbing CO2 from ing from new carbon input and that derived from the atmosphere and thus sequester carbon [9]. fossil-based input. A measurement of the 14C/12C ratio is determined relative to the modern carbon- based oxalic acid radiocarbon Standard Reference Material (SRM) 4990c (referred to as HOxII), as Determination of Bio-Based the oxalic acid standard is 100% bio-based. The Content in Polymers percent new carbon can be slightly greater than 100% due to the continuing (but diminishing) Bio-based polymers can be made totally or par- effects of the 1950s nuclear testing programs. tially from renewable source raw materials, pro- Because all sample 14C activities are referenced to duced from photosynthesis and CO2. In order to a “pre-bomb” standard, all modern carbon values determine the bio-based content of the polymer, the must be multiplied by 0.95 to correct for the bomb “new” carbon content must be measured. A renew- carbon and to subsequently obtain the true bio- able source is replenished by natural processes at a based content of the sample [11]. rate comparable to its exploitation rate. The carbon CEN/TS 16137 specifies the calculation method content of such polymers is derived from the so- for the determination of bio-based carbon content called short carbon cycle within an expected time in monomers, polymers, plastics materials and pro- frame between 1 to 10 years. Most industrial poly- ducts using the 14C method based on three test mers and plastics are presently produced from fossil methods: (a) Proportional scintillation-counter resources that are non-renewable as they cannot be method (PSM); (b) Beta-ionization (BI); and replenished at a rate comparable to the exploitation (c) Accelerator mass spectrometry (AMS). The ana- rate. Fossil resources have a long carbon cycle, lytical test methods specified in this Technical with an expected time frame to convert biomass to Specification are compatible with those described petroleum, gas, and coal of greater than 106 years in ASTM D6866-11. The bio-based carbon content [10]. The accepted measure of bio-based content is is expressed by a fraction of sample mass, as a frac- the level of 14C isotope in the feedstock (basically, tion of the total carbon content, or as a fraction of 15: BIOBASED THERMOSETS 579 the total organic carbon content. This calculation hydrophobic or amphiphilic (both hydrophilic and method is applicable to any polymers containing lipophilic) small molecules. Different plant species organic carbon, including bio-composites [3]. contain lipids with different fatty acid compositions Calculation of percentage of bio-based content and distributions. Lipids help form a hydrophobic according to CN/TS 16137:2011 is based on the biological membrane that separates cells from their calculation of carbon content as a fraction of the surroundings and keeps chloroplasts, mitochondria, total organic carbon content (TOC) expressed as a and cytoplasm apart, thus preventing or regulating percentage, using Equation (15.1): diffusion of chemicals [14]. Plant oil is a mixture of various triglycerides XB;TOC 5 ðXBÞ=ðXTOCÞ (15.1) (also called triacylglycerol). One glycerol is attached to three different fatty acids to form a tri- Here, XB 5 is the bio-based carbon content by glyceride. Glycerolipid and fatty acids are synthe- mass, expressed as a percentage; and XTOC 5 is the sized in the oilseed simultaneously during seed total organic carbon content, expressed as a per- development, before forming diacylglycerol and centage, of the sample. subsequently triacylglycerols. Triglycerides are composed of three fatty acids joined at a glycerol juncture, as can be seen in Figure 15.1. Fatty acids Raw Materials for Renewable account for approximately 95% of the total weight of triglycerides and their content and chemistry are Sources Polymers characteristics of each plant oil and geographical Natural Oils conditions [15]. The most common oils contain fatty acids that vary from 14 to 22 carbons in Natural oils, which can be derived from both length with 0 to 3 double bonds per fatty acid. plant and animal sources, are considered to be one Fatty acids derived from nature have even an num- of the most important classes of renewable sources ber of carbons due to their biosynthesis (acetyl because of the wide variety of possibilities for coenzyme A, two carbon carrier).