Cellulose Again

Cellulose chain courtesy Wikipedia

The  story of plastics actually began with cellulose,  way back during the last two decades of nineteenth century.   Cellulose,  isolated from wood pulp  was subjected to serious chemistry and Hyatt Manufacturing Company brought out celluloid in 1870.  This was cellulose nitrate  made  sufficiently pliable by adding small amounts of camphor.  But the material had a huge drawback; it was a fire hazard,  it burst into flames spontaneously  at the slightest provocation.  In fact its more popular name was gun cotton and often substituted for gunpowder.   Its meeker cousin cellulose acetate  was  synthesised by French chemist  Paul Schutzenberger.  The credit for taming cellulose acetate and unravelling several of its  useful qualities goes to two siblings Camille and Henri Dreyfus.  They found that cellulose acetate  could be made into neat protective films, spun into fibres,  and could also be injection moulded  into any desired  object.  In 1912  Swiss chemist Brandenberger perfected the art of making cellophane a thin transparent  film which revolutionised the packing industry.   But the golden period of cellulose plastics  was short lived.  The two world wars  demanded  cheaper, more versatile plastics  and the petrochemical industry generously provided cheap raw materials  for  the nylons, polythenes, polyesters, polyurethanes, polycarbonates etc.....  Cellulose was marginalised  for limited  applications.

Courtesy :wikipedia

In a recent comprehensive review   Tian Li and coworkers  highlight the need to relook at cellulose. They build a case particularly for cellulose fibres downsized to smaller free standing  fibrils. Such  microsized or nanosized fibrils  could be  made into  transparent papers with gloss and texture,  excellent for various  packaging applications.  This biodegradable material could prove to be the best alternative  to  the  millions of tons of nondegradable plastic garbage we keep  accumulating on a daily basis. 

These fibrils could also be excellent reinforcing materials.  Cellulose has an abundance of hydroxyl groups  which can form  extensive intra and inter chain  hydrogen bonding. Such  networks can  improve the mechanical properties of composites.  It has since  been established that  nano cellulosic fibrils perform far superior to conventional micro size  fibrous  reinforcements in composites. Japan's Ministry of Environments has already taken note of this and initiated Nano Cellulose Vehicle Project (NCV) to develop lightweight automotive components.  Calculations show that a 10% reduction in the weight of the vehicle  could  reduce fuel need by about  6%.  

Though cellulose is a plentiful, renewable resource,   challenges remain.  One that tops the list is the energy and cost intensive steps involved in the  isolation of cellulose  and its subsequent  processing  into  nano form. Global teams are at work to tackle this challenge.    Researchers at the  Edinburgh Napier University in collaboration with South African Paper and Pulp Industry (Sappi)  seem to have developed a  cost effective process  to turn wood pulp  into  "nanomaterial that could be used to build greener cars, thicken foods and even treat wounds".

REFERENCES:

1. "Developing fibrillated cellulose as a sustainable technological material. Li et    al.; Nature  590,pp 47-56, 4 February 2021

2. Tokyo Motor Show 2019: NCV (Nano Cellulose Vehicle Project)

3. Conversion Economics of Forest Biomaterials: Risk and Financial Analysis of CNC Manufacturing

4. A New Low-cost Process to Make Nano cellulose

4.American Process: Production of Low Cost Nanocellulose for Renewable, Advanced Materials     Applications.  

In the Sea, on the Land or Somewhere in between?

 Exactly 150 years ago on 1st February 1871, Charles Darwin wrote  to a colleague : 

"But if (and oh what a big if) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts,—light, heat, electricity &c. present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter wd be instantly devoured, or absorbed, which would not have been the case before living creatures were formed." 

Eighty years later in 1952 Stanley Miller and Harold Urey translated Darwin's thoughts into an experiment. Using water, methane,  ammonia, hydrogen and electric spark to mimic lightning, he synthesised amino acids, the building blocks of proteins. The hypothesis of oceanic primordial soup containing all possible chemicals  subjected to  Sun's ultraviolet rays and occasional lightning  giving rise to life's molecules gained  wider  acceptance.  

Miller-Urey  Experimental set up
Courtesy:wikipedia

But almost immediately  everything changed. The 1953 Nature paper by Watson and Crick established  deoxyribonucleic acid, DNA for  short,  as the macromolecule of life with the   genetic code   encrypted in a unique way in the DNA chain using 4 nucleobases: adenine, guanine, thymine and cytosine. In 2017, a group of scientists  repeated the Miller-Urey experiment  with suitable modifications and demonstrated that abiotic synthesis of nucleobases is also possible.  And then RNA replaced DNA as the original molecule!

The prebiotic soup model  has thermodynamic as well as kinetic   inconsistencies.  Issue is   not the formation of the building blocks, but the process of linking them and sustaining these linkages in a vast and seemingly limitless waterbody.  The  peptide bonds,  and the phosphodiester bonds, which form   the backbone of the proteins and  nucleic acids respectively,  are  both  extremely susceptible to water.  Biochemist Robert Shapiro  a vehement critic of the  primordial soup hypothesis  stated: "And of course the apparatus itself has no resemblance whatsoever to the primitive Earth. One of the popular magazines said that if this apparatus had been left on for a million years, something like the first living creature might have crawled out of it. And I say, if he'd left his apparatus on for a million years, he would have run up one hell of an electric bill " . 

Nonetheless the primordial soup model prevails, of course with modifications. For example  Professor John Sutherland  feels that small shallow ponds filled with  primordial soup,  and which have a tendency to dry out and refill might be a possibility.   The clay bed of such a pond  subjected to  periodic wet and dry cycles together with light and dark cycles of day and night would coax/catalyse  molecules to form, organise, hold together  and grow.  If the clay is rich in minerals such as quartz, then the issue of chirality could also be somewhat  settled. Because  as professors  Hazen and Sverjensky point out "such surfaces may have contributed centrally to the linked prebiotic problems of containment and organization by promoting the transition from a dilute prebiotic “soup” to highly ordered local domains of key biomolecules". 

Anthropogenic activities have irreversibly contaminated all possible terrestrial sites hence 

Professor Sutherland   is pinning  hopes on Perseverance, the rover  heading towards Mars.  Perseverance is programmed to land in the Jezero crater in Mars and collect and bring back  soil and rock samples. The assumption is that 3.5 billion years ago  this  crater could have been  a water body that underwent wet-dry cycles and  hence a faint probability that it could have supported life.  Scientists hope that Martian rocks and soil samples might hold secrets of  life,  that  the ancient biosignatures inscribed in there  might still be decipherable. 

Are we  going a bit too far ?

REFERENCES:

1. Life and Letters (Darwin 1887, Vol 3:168–169)

2. Miller SL (1953) A production of amino acids under possible primitive Earth conditions.           Science 117:528–529.

3. Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions 

4. Formation of nucelobases in Miller-Urey reducing atmosphere.

5. A Simpler Origin for  Life   

6. Mineral surfaces, Geochemical complexities and the origins of Life

7. Chance, necessity and the origins of Life 

7. Perseverance Rover's landing site: Jezero Crater