Agro- residues: Beyond waste, potential fibres for textile industry

Written by: Preeti Kaur Sachdeva~Bhawana Chanana~M.S. Parmar

Do we need to shift our focus from traditional natural cellulosic textile fibres to innovative textile fibres like bagasse, pineapple leaf, cornhusk, water hyacinth? Preeti Kaur Sachdeva, Dr. Bhawana Chanana and Dr. M S Parmar examine reports and study to find out.

 

What is waste? As Tom Szaky said, "On looking at waste as an entirely modern, man-made idea, I stopped viewing garbage as garbage and instead started to see it as a commodity."

 

In India, agriculture provides 54 per cent employment in rural as well as urban India. The total share of agricultural output in terms of percentage of Gross Domestic Product (GDP) was 13.9per cent during 2013-2014 at 2004-05 prices. Total estimated agricultural crop production for the same year was 264.77 million tonnes. After the isolation of the main agricultural product, abundant solid residue is generated. Worldwide, it is common practice to dump residue as garbage. The piles of residue decompose by microbial activity and become a nuisance for the environmental health. Industries use agricultural residues for co-generation, but these residues being of low calorific value, generate smoke and pollute the environment on burning.

 

Burning agricultural residue in the agricultural field has been common practice throughout north India. It produces lethal smoke leading to respiratory diseases. Recently, the National Green Tribunal (NGT) banned such burning and declared such practice illegal and fineable. Now, all stakeholders have to think of novel and sustainable methods to utilise the idle, underutilized resources that are of important economic value to India.

 

Rice, wheat, sugarcane, soybean, corn, banana, pineapple, bamboo and okra are a few examples of crops that generate considerable residues. These contribute to the major part of the total annual production of biomass residue and are an important source of long and short fibres rich in cellulosic content.

 

What are agro-residues?

Agricultural residue or agro-residue describes all organic material produced as by-products after harvesting and processing agricultural crops. Agro-residues are non-wood lingo-cellulosic and a rich source of cellulose with lignin. These may include stalk, cane, seed pod and leaves. Agro-residues are annually renewable and a low cost source for natural cellulosic fibers. Agro-residues are of two types.

 

Figure 1: Classification of agro-residues

 

Field residues: These are materials left in an agricultural field after the crop has been harvested. Examples include pineapple leaves, banana pseudo stems and leaves, cornhusk, cotton seed pods, kapok seed pods and cotton stalks.

 

Process residues: They are materials left after the crop is processed into a usable resource. After isolation of the primary or main agricultural product, a huge volume of residue is generated simultaneously. Examples of process residues are bagasse, pea peel, wheat and rice straw.

 

Worldwide, leaders are discussing the alarming issue of climate change and its subsequent consequences. To promote sustainable living, nations are striving to work primarily on climate change, affordable and clean energy alternatives and efficient waste management.

 

Availability of agro-residues

Quantifying the amount and type of agricultural residues generated in each crop category is difficult, as it would require conducting comprehensive research with continuous updates of compiled data. The minimum worldwide availability of various agro-residues in the year 2000 as was estimated by the Agricultural Residue Committee is given in Table 1.As per the data released in 2009 by The Ministry of New and Renewable Energy (MNRE),approximately 500 metric tonnes (Mt)of crop residues are being generated every year in India. There is a wide variability in the generation of crop residues and their use across different regions of the country depending on the crops grown, cropping intensity and productivity. Generation of crop residues is highest in Uttar Pradesh (60 Mt) followed by Punjab (51 Mt) and Maharashtra (46 Mt).

 

Table 1: Proximate Worldwide Availability of Agro-fibres in Million Tonnes (MnTn)

 

Conventionally, almost all agro-residues have been burnt for energy generation in boilers. But being low-calorific fuel, they generate air pollution due to which their use for energy generation is prohibited by Pollution Control Board. Currently, they are generally disposed of either by composting or by burning in the fields. Ina developing country like India, every possible effort should be made for the proper utilisation of these agro-residues as they are rich in cellulose and renewable. As stock is abundant, the price of agro-residues is cheaper than that of conventional cellulosic fibres like cotton, jute and linen13.

 

Conventional Uses of agro-residues

Conventionally, agro-residues are used for many purposes which are often are site-specific. Depending on how and where the crop is harvested, the ultimate use of agricultural residues varies. Besides being used as fuel, other uses of agro-residues are as fodder, fertiliser, fibre, and feedstock. As fertilizer and soil conditioner, coconut coir dust is used to retain moisture in the soil and straw as a growing medium for mushroom. Coconut husk is used as a growing medium for orchids and for packing material. Rice husk has many uses. It is burned as fuel. Ash generated is used by the steel industry as a source of carbon as well as insulator (feedstock). Also rice straw is used as animal bedding (fibre) and subsequently as part of compost (fertiliser), crop waste can be used as a feedstock for biogas generation (fuel), with the sludge being used as fertiliser. However, use of such agro-residues is limited or mostly unexplored in the textile industry. As it is a technically high-end industry, sophisticated technology needs to be devised and made available for extraction and application of the cellulose rich fibres from agro-residues to be made and used as textile goods.

 

Agro-residues: Alternative fibres for textile industry

Upkeep of the environment is of vital concern to Indian authorities. Agriculture industry is producing agricultural waste in million tonnes annually. Successful solid waste management and proper utilisation of these residues is a major challenge. A similar challenge is being acknowledged by the textile industry. It is the second major sector providing employment in India.

 

The Indian textile industry is primarily cotton-based, cotton accounting for 54per cent of total fibre consumption in 2014. Cotton is one of the most economically and ecologically expensive commercial crops to produce. Cotton production is the second largest agricultural use of pesticides in the world with five of the nastiest pesticides used. Cyanide, dicofol, naled, and propargite are mainly used in cotton cultivation and these chemicals are known to be cancer- causing apart from being environmentally dangerous. Cotton still accounts for 60 per cent of the total fibre production of the world, although man-made fibres have made significant inroads into cotton's share during the last three decades. The population boom is pushing demand for cotton exponentially. China is a major buyer of cotton yarn from India. A leading daily reports that the Indian cotton industry registered a record 142,297 tonnes export latest by June 2013. A billowing surge of 73per cent from last year in cotton export was recorded. This has left India's domestic cotton market hand-to-mouth. This situation is aggravated and compounded by rising price of cultivating cotton and other natural cellulosic fibres like jute and linen. It is the need of the hour to look out for alternative cellulose resources. To address the critical situation, there is a requirement of substitutes to conventional cellulosic fibres, which are environmentally expensive to produce. Some of the undervalued but easily accessible agro-residues are being presented here.

 

The major constituents of all cellulosic fibres are α-cellulose, pentosan and lignin. High α- cellulose and low lignin content of a fibre are necessary for its application in textiles. The cellulose availability in agro-residues is in the form of a complex where cellulose is encrusted in the layers of hemicellulose and lignin. Both cellulose and hemicellulose are carbohydrate polymers while lignin is an aromatic polymer. However, to obtain natural fibres with pure cellulose, it is imperative to process the agro-residues for the maximum removal of hemicellulose and lignin. In utilisation of cellulose in agro-residues, these two polymers (hemicellulose and lignin) act as impurities.

 

Besides the availability of pure cellulose, other factors which influence the development and utilisation of these lingo cellulosics in textile industry are:

a. Ability to be spun

b. Sufficient quantity

c. Cost or economy of production

d. Desirability of their properties to consumers

 

The biochemical composition of agro-residues varies owing to the composition of the crop from which they are sourced and the crop-specific environmental conditions they are grown in. Han, 1998, has reported on how the chemical and physical properties of some non-wood fibres are influenced by fibre growth time (days after planting), botanical classification of fibre, stalk height, environmental conditions, rainfall, etc. The pure cellulose component of these agro-residues has the potential to be used in textile industry either as natural cellulosic fibre or as regenerated cellulosics. Though it is a well-acknowledged fact,it was hardly exploited owing to lack of dedicated research and technology.

 

Bagasse and bamboo are two important stalk agro-residues, and cornhusk and banana leaves are important leaf agro-residues. The cellulose and lignin composition of the four residues testifies that bagasse holds the highest amount of processable cellulose (57per cent) amongst all other residues (Table 2).

 

Table 2: Proximate chemical analysis of some common agro-residues

 

Bagasse

One of the largest cellulosic agro-industrial by-products is sugarcane bagasse (or bagasse). It is a fibrous residue of cane stalks left over after the crushing and extraction of the juice from sugar cane. The quality of bagasse is dependent on the variety of cane, age of cutting, agronomic and soil conditions and the extent of crushing and milling operations carried out. It is a ligno-cellulosic residue (by-product) of the sugar industry and used by the sugar factories themselves as fuel for boilers. India is a major producer of sugarcane bagasse which is an annual process residue of sugar mills apart from cornhusk, wheat and rice straw.

 

Bagasse is a multi-cellular and lingo-cellulosic cane fibre. Crude bagasse contains about 65-70per cent useful fibre and about 30-35per cent pith, dirt and other water soluble material. Pith is an undesirable fraction because it contains non-fibrous cells, which are below 0.4mm in length. Further, pith consumes huge amount of chemicals leading to wastage and clogging. Hence, bagasse has to be de-pithed for industrial application. The biochemical composition of de-pithed bagasse indicates that it contains about 57 percent α-cellulose, 19 percent lignin, 24 percent hemicellulose, evincing its suitability for producing good quality natural cellulose fibres and pulp under controlled conditions26. The chemical composition of bagasse varies with sugarcane varieties, plant maturity and soil properties24.

 

For every 10 tonnes of sugarcane crushed, a sugar factory produces nearly 3 tonnes of wet bagasse. Since bagasse is a byproduct of the sugar industry, the quantity of production of bagasse is in line with the quantity of sugarcane produced. Studies reveal that about 54 million tonnes of dry bagasse are produced annually throughout the world. In general, sugar mills generate approximately 270 kg of bagasse (50per cent moisture) per metric ton of sugarcane.

 

Bagasse is considered as a rich natural resource when compared to other agricultural residues because of its high yield and annual regeneration capacity. The biochemical composition represents bagasse as a potential and abundant cellulose resource. To put bagasse to some useful industrial applications, it is imperative to extract pure cellulosic fibres free off hemicellulose and lignin which act as impurities.

 

Bagasse has not been the subject of much research worldwide. Some research studies were taken up at Louisiana State University. An important research effort in previous work was extraction of sugarcane rind fibre for textile applications. The extraction of fibres was done by alkalisation. Collected bagasse was subjected to sodium hydroxide under specific pressure. The extracted sugarcane rind fibre was used for making geotextile mats for soil erosion control. It was reported that the sugarcane fibre mats had higher water resistance, lower light penetration, and were less flammable than commercial geotextile products. Similarly, in various other studies, bagasse fibre has been reported to be used for nonwovens but there is no literature on the spinning of bagasse fibre.

 

Cornhusk

Corn is a member of the grass family of plants and the most widely distributed crop in the world. It is the largest food crop in the world and the United States produces about 40per cent of the world corn production. Based on the annual world production of corn, about 45 million tonnes of cornhusks are available every year. More than 9 million tonnes of natural cellulose fibres suitable for textile applications can be extracted from them every year. This makes cornhusk fibre second only to cotton in terms of natural cellulosic fibre. Corn husk, one of the byproducts of corn production, contains about 39-42per cent cellulose which can be extracted in fibrous form for various industrial applications, including textiles. Although textile applications offer a relatively high value addition and a huge market for cornhusk fibre, they require fibre of high quality. Reddy (2005) has for the first time attempted to extract natural cellulosic fibre from corn husk with strength and elongation between cotton and linen. Fibres were extracted manually due to lack of any suitable mechanical process. Researchers state that the extracted fibres have the potential to be the cheapest available natural cellulosic fibre for textile applications and would be second only to cotton in terms of availability. Hydrolysis alkalisation was done to obtain fibre from cornhusk. Fibres were cooked at varying concentrations of sodium hydroxide to obtain long cellulosic fibre free of lignin and hemicellulose. In further investigation the same research group examined the compatibility of cornhusk fibre with cotton and polyester on ring and rotor spinning machines. Cornhusk fibre blends with cotton were developed in the weight ratio of 80/20, 70/30 and 50/50 and with polyester in the weight ratio of 65/35.

 

Socio-Economic Perspective

There are regions where these abundant agro-residues are still a waste. These valuable agricultural residuals are being burnt in lack of any alternative commercial use of them. Farmers are losing additional income while their counterparts in the region where small and medium scale handloom industries exist and significantly contribute in income generation.

 

Exploring a feasible application of agro-residues will lead to environmental as well as socio-economic benefits to the farmer. So, agro-residues can be instrumental in increasing farm income. The prices received by the farmers may help them strengthen their economics. Devising technology for efficient utilisation of these agro-residues will not only support the rural community by adding value to their products, but also protect the environment. We need robust cooperation between industrialists and research groups with consistent efforts and genuine concern for the development of use of agro-residues.

 

Although textile applications offer a relatively high value addition and a huge market for consumption of fibres from agro-residues, they require fibres of high quality. Versatile application of agro-residues in textile industry depends on the fineness and strength of fibres produced. Extraction of quality fibres depends to a large extent on extraction techniques employed. Therefore, existing extraction methods need to be supplemented with robust techniques and machinery to provide the agro-residues like bagasse and cornhusk with value worth advocating. It is sometimes assumed that residues are wastes and therefore, more or less free of cost. However, it is unwise to assume so. In a monetised economy, even where residues are freely available, everything which has a use will sooner rather than later acquire monetary value.

 

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About the authors:

Preeti Kaur Sachdeva is senior research fellow at Lady Irwin College, University of Delhi, New Delhi.

Dr. Bhawana Chanana is professor and Director, School of Fashion Design & Technology, Amity University, Mumbai.

Dr. M. S. Parmar is professor and Director at Nitra Technical Campus, NITRA, Ghaziabad.