Well into the nineteenth century, biomass was a main source
of materials and energy in most countries. The rapid development
of petrochemistry in the twentieth century led to a
shift from biomass to fossil carbon (coal, oil, gas) as the major
source of fuels as well as of building blocks for the generation
of a wide variety of chemicals and materials. The worldwide
share of biomass in energy production is around 10% and
biomass still plays a significant role in some OECD countries,
such as Sweden and Austria. However, fossil carbon is currently
the dominant source of both energy and the materials
on which our society depend.
Climate change and resource constraints now force us to
reconsider the use of plant biomass as a source of materials
and fuels. However, it is well known that prior to the nineteenth
century, overuse of biomass led to deforestation, soil
degeneration, and desertification. In the early twenty-first
century, the world fed, clothed, and sheltered almost 7 billion
people instead of the 1 billion population at the start
of the nineteenth century, while increased wealth, changed
habits, and excessive consumption drastically increased the
per capita use of energy and materials. At the same time,
increasing droughts and changes in weather patterns linked
to climate change have reversed the decades-long trend of
increased global plant growth, according to a new analysis of
NASA satellite data (Zhao and Running, 2010); ocean acidification
threatens to destroy marine ecosystems providing food,
feed, and materials (Fabry et al., 2008); global biodiversity is
collapsing (Ehrlich and Pringle, 2008); and human appropriation
of net primary production (fraction of the net amount of
solar energy converted to plant organic matter through photosynthesis,
used or lost by human activity, HANPP) may have
already reached 50% (Erb et al., 2009). The inescapable conclusion
is that biomass is a limited resource that should be put
to the best (and most efficient) use possible.
Since mankind now depends on fossil fuels for 80–90%
of its energy demands and the present level of biomass use
is already critically high, biomass cannot provide more than
a few percent of present fuel consumption, especially if the
greenhouse gas balance and other unwanted side effects (soil
degradation, water use, eutrophication, loss of nature, loss of
jobs) are taken into account. It is evident that bioenergy will
not be a major solution to our energy and climate change predicament;
energy (carriers) for transport and heating will have
to come from other, non-biological, sources.
The story is different for carbon-based materials, because
most major polymers and chemicals depend on a source of
carbon. If fossil fuels are no longer available, affordable, or
their use politically acceptable, the chemical industry must
become based on heterogeneous biomass sources (agricultural
and forestry waste) or well-defined biomass fractions (sugars,
starch, cellulose, vegetable oils, etc.). The first option is complicated
by the necessity to maintain soil carbon content and
fertility, while the latter competes with the food market as it is based on existing crops. A completely different scenario is
based on the assumption that there will be sufficient oil available
for chemicals and polymers if it is no longer squandered
as fuel. Ultimately, the question is one of deciding between
scenarios, and life cycle analysis is essential in deciding what
works best.
Several recent reviews have focused on the specific products
(chemicals, polymers, bioactives) that are produced in
plants (van Beilen, 2008; Sharma and Sharma, 2009; Bornke
and Broer, 2010). This chapter focuses on the biopolymers.
The first section covers major biopolymers based on naturally
produced plant polymers that are applied widely in industry.
The second section discusses efforts to produce new polymers
in transgenic plants, discussing their promise and potential
shortcomings. The multitude of minor plant and algal biopolymers
is not discussed here.