Poplar Fluff: Unlimited Source of Advanced Materials

In Kashmir there are around 15 million poplar trees with an estimated volume of around 5,30 million cum.
Poplar Fluff: Unlimited Source of Advanced Materials
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Genus Populus is one of the most spread taxa in nature with around 25-35 sub-species, 500 hybrids and more than 2.0 lakh clones. Populus deltoides (Eastern Cottonwood) is the main poplar species planted in India. A major share of its plantations is made in a 1000 km narrow belt located in the Indogangetic plains south of the Himalayan foothills.

Over 30 million poplar saplings are planted by around sixty thousands farmers annually in and around their agricultural fields. In Kashmir there are around 15 million poplar trees with an estimated volume of around 5.30 million cum.  Misquoted as Rousee frass, P. deltoides comprises more than 90 percent population of poplars in Kashmir. The majority of these trees are female cultivars which produce cottony seeds mistaken as pollen that causes allergy and other health hazards. The pollen is produced by male trees and the females are the receptors of this pollen to produce seeds – our food security depends on this process (pollination). Genetically improved clones of the poplar trees were introduced by Social Forestry department during the year 1984 and planted intensively but randomly (without any gender records) throughout the valley for production of wood to support fruit industry that consumed around 3.00 lakh conifer trees annually at that time. The trees were also planted for protection against erosion and as natural water pumps around the polluted water sources. Poplar wood has also been supplied and used for plywood and match industry and lately entered in timber industry to replace Fir and Spruce in roofing of houses. 

Presently poplars are a 600 crore industry in our State supporting livelihood of both urban and rural habitations. Despite this huge economic potential, poplars are not appreciated particularly in urban areas because of their fibrous seeds appearing during blooming in late spring and which remains floating around in the atmosphere to cause inconvenience rather than allergy for which it is blamed. The best possible solution to resolve this problem would have been to adapt the short rotation forestry  with 3-5 or 8-10 years harvesting schedule (juvenile age) as followed around the world with production rate of 10-30 m3 ha-1 yr-1. But thanks to stake holders for not developing such type of industrial sector in this region.  Here in Kashmir we have been managing poplars on a harvest cycle of > 20 years (a reproductive age) that too without following any pruning schedule. These trees produce large quantities of sterile seeds embedded in a dispersal mechanism of fluffy material.  These seeds which until now are being treated and as annoying pollutants in this part of the world, have found many uses and with the latest developments in Europe and America this fluff is now actually considered as a precious natural material (fibers) with unique morphological structure applicable in modern technology, as for example, production of natural super sorbents or smart medical materials. 

On an average one poplar tree produces 35 liters of fresh fruits which yields from 280,000 to 14,850,000 of seeds (0.9 kg) depending on species, location and type of the tree. More than 7,029,000 hectares of poplars are planted (on average 500 trees per hectare) around the world for wood production (FAO). This is a huge unexploited natural source of raw material for production of high tech materials. As mentioned, the fibrous poplar seeds are treated as waste or, in the best case, used as a cheap fertilizer. The estimates by international poplar commission (IPC) have shown that from the over 7 Mio Ha of poplar planted in the world over 3 Mio tons of high quality fibers can be produced. Such poplar seed fibers (PSF) presents an almost unlimited source of high quality fibers for the production of advanced materials and at the same time their use presents reduction of greenhouse gasses. "Poplar trees unlimited source of Advanced Material (PAM)" project predicts that Europe can be a strategic producer of natural fibers for production of advanced materials. Production of hydrophobic fibers is cheap and clean and requires additional human resources for cultivation and harvesting, creating more job opportunities in agricultural sector. Business opportunity can thus be created through the establishment of production and merchandising network for poplar fibers to become industrial commodity of advanced materials. 

Poplar fibers have been proved to be extremely light, hydrophobic, possess large active specific surface area and float on water surfaces without long term degradation, even when soaked with hydrophobic liquids. Research has showed that poplar seed fibers are a natural source for production of different high tech fibrous materials as for example oil super sorbent, insulation material, ultra-light packaging, smart medical materials, drug delivery agents and other products where hydrophobic fibers must be used. The solid skeleton of hollow fibers have been shown to consist of lignocellulosic material coated with hydrophobic waxy coating with active surface area of 2.42 ± 0.16 m2 /g and can effectively replace extremely expensive hydrophobic nano cellulose fibers. Fibers derived from the poplar seeds are, by their nature, hydrophobic/oleophilic micro tubes with 8.74 ± 5.75 μm of outer diameter composed by 33-37 % of cellulose, 19-22 % of hemicelluloses (manly pentosans), 10-12 % of lignin and 1 -2 % of inorganic substances (Marko likon, 2015). 

This study has further revealed that the bulk density of the fibers is 0.0036 g/cm3 as 89 vol. % of the fiber is empty lumen that tends to be filled with hydrophobic/ oleophilic substance when the fiber comes into contact with this substance. Hydrophobicity of the fibers is increased due to a coat of fiber surface with natural waxes. Fibers express improved resistance to gel blockage and higher mechanical resistance against collapse. They are chemically and biologically stable if properly harvested and stored. The conducted Life Circle Assessment has shown that, due to the wild and fast growing nature of poplar trees and a high ratio of binding of carbon during growing processes, the use of poplar seed fibers for the production of technological products expressed a negative carbon foot print and served as a natural reduction for carbon dioxide. Those fibers indeed are the only known sorbent material which expresses a negative carbon footprint on the globe. Taking into account PSF's higher sorption compared to the expanded polypropylene and their production from renewable sources, poplar seed fibers are environmentally much more sustainable than other synthetic sorbent materials existing in the market. 

Marko likon has stated that a comparative analysis conducted on different sorbent absorbents confirmed that poplar seed fibres are 7.5-fold more efficient than expanded polypropylene, which is the industry standard for water surface recovery. Poplar seed fibres, kapok seed fibres, silanized cellulose and expanded polypropylene have fully passed the degradation test in accordance with the ASTM 726-06 "Dynamic Degradation Test". At the moment the main barrier for commercialization are the harvesting processes. Still we must assure critical quantities of raw material needed, can be procured by expanding the harvesting network and improving of harvesting technology. Use of poplar seed fibers for super sorbents and ultra-light insulation and packaging material is the first known use for production of advanced materials with high added value and low carbon footprints. 

It is an interesting example of how a "waste" of agriculture is exploited for production of advanced materials with high added value and low carbon foot print which can be used in different public and industrial sectors as in medicine, disaster relief services and in construction, oil, chemical and logistic industry. Indeed these fibers can replace expensive and complex synthetic materials. This is how a pollutant in Kashmir is put to commercial use in Europe – not to fell trees by yelling at them like in Solomon Islands where it's believed that large trees are not felled by axe but killed by hollering at the peak of lungs at dawn for 30 days. I hope poplars will not face the same fate.

(Author is a Professor in Faculty of Forestry SKUAST, Kashmir. Feedback at drthmasoodi@gmail.com) 
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