Biobased Polyolefins

Braskem, a Brazilian company, began producing biobased polyethylene on a commercial scale in 2010 [7]. The starting material is sugar cane. Conventional fermentation methods are used to produce ethanol from sugar. Ethanol is then dehydrated to ethylene. This ethylene can then be used to produce polyethylene, exactly as is done with ethylene from petrochemical sources. The resulting polyethylene is identical in performance to conventional polyethylene, and of course is not biodegradable. 

The only significant difference between biobased and petro-based polyethylene is the ratio of C to in the molecules. This ratio is the basis for carbon dating, as the amount of this isotope in an object decreases with time due to radioactive decay. The new carbon coming from the plants has higher levels of carbon 14 than the old carbon in oil or natural gas. 

Braskem is also planning to introduce biobased polypropylene. The same basic idea can be used to produce any plastics that are derived from ethylene, from any source of sugar or starch. Of course, cost remains a major barrier. 

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As is the case for biobased polyolefins, the production of the polymer from the biobased monomer is identical to production of petro-based PET, and the resulting properties are identical (except for the ratio of carbon isotopes, as discussed above). Several routes to terephthalic acid are currently under consideration. They include routes through isobutanol, para-xylene, and muconic acid, derived from various plant sources. 

At room temperature, the mechanical properties of PLA are close to the one of PS but smaller than the one of PET (Table 8.5). Polyolefins present reduced stress at yield compared to PLA but the strain at break of LDPE and HOPE are much higher than the one of PLA. Compared to another biobased polymer, poly(hydroxybutyrate) (PHB), PLA shows better mechanical properties with higher modulus of elasticity and stress at yield. 

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