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You are here: Home > Technique > Processes > Scientific report of the LGP2 > Packaging and converting > Valorisation of different agricultural crops in papermaking applications           Update: April 26th 2007
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Researchers of the LGP2 (EFPG, INPG, CNRS, CTP)
(November 2006)
 
Documents taken from the
"Scientific Report of the Laboratory of Pulp and Paper Science and Graphic Arts - UMR 5518
Grenoble - France
January 2002-November 2005"

V - Packaging and converting

V - 4 - Valorisation of different agricultural crops in papermaking applications
Séverine Schott, Didier Chaussy, Évelyne Mauret, Isabelle Desloges, Naceur Belgacem

This thematic deals with the use of different agricultural crops as a source of lignocellulosic fibers in order to produce papers for corrugated boards.

1 - Wheat straw pulps

This study bas been initiated by the French Ministry of Agriculture, Food and Rural Affairs and bas been carried out in collaboration with EMC2, who developed and patented a steam explosion pulping process. Wood fibres are presently the most widely used in the world pulp and paper industry. Yet, the use of non-wood fibres still initiates research in many countries. In Europe, the development of non-food applications for agriculture, in particular for agricultural residues, leads wheat straw to be reconsidered as a raw material for the papermaking industry.

First, we were interested in the characterisation of the steam exploded wheat straw pulp. This pulp has high hemicellulose (23%) and fine particles (60% below 0.68 mm) contents. As a consequence, even before beating, the pulp presents a low drainability (around 35 °SR) and a high hydration degree (WRV around 2 g/g). lt has also been shown that the beating of the pulp enhances the mechanical properties of paper; especially the SCT CMT and Scott Bond values. Moreover, the screening of the pulp is crucial; it increases the strength properties between 15 and 25%. Therefore, the use of steam exploded wheat straw pulp in mixture with waste papers seems to be interesting for the production of wrapping papers. Then, our research has been orientated towards mixtures of wheat straw and recycled fibres pulps. The beating, wetpressing and drying processes bave been studied, with blends containing 0, 10, 30, 50 and 100 % wheat straw pulps. Adding wheat straw pulps to the stock increases paper strength. The increase is higher when the pulps are beaten separately. Yet, it also decreases the wet-pressing efficiency, which leads further to a slower drying of the sheet. This work also contributes to a better understanding of pulp blends.

Several industrial trials have been conducted in the field of corrugating and winding papers. Around 100 tons of paper have been produced, without any problem. The board characteristics bave been improved, but the productivity bas been reduced (lower machine speed and higher vapour consumption). Nevertheless, the products can be economically viable by choosing the proper furnish composition, the appropriate retention and dewatering aids and by optimising beating and wet pressing processes. Yet, attention should also be paid to dimensional stability and recycling potential of papers made from steam exploded wheat straw pulp and waste papers.

Finally, these results completed with those previously obtained on others raw materials led to a better understanding of key parameters which influence the compressive strength of paper, particularly the Concora Medium Test (CMT) value of the medium. The purpose of this study is to remind the main phenomena occuring during compression and to determine the major factors affecting the paper compressive strength. A theoretical estimation of the CMT value is considered, with regard to pure compression and buckling. Based on the testing of more than 250 different raw materials, the main factors are determined, and calculation formulas are established. For example, the CMT can be expressed, with good precision, as a function of stiffness and z-directional tensile strength (see Following Equation). These results are of value for a practical evaluation of the end-use properties of corrugating medium. They introduce parameters which enable the optimisation of production, for instance the choice of raw materials, chemical aids and papermaking processes.

R˛ = 0.84
MRE = 9.9 %
(Mean Relative Error)
With Et, tensile Young's modulus (GPa)
et ZTS, Z Direction tensile strength (kPa)

2 - Pulps from Banana's crops

Banana plants Musa accuminata Colla, grown in Madeira lsland (Portugal), is the most wide spread species occupying almost 77% of cultivated area and is the major economic source of the lsland (1/3 of the total exportations and 20 % of the income). This activity produces a big quantity of agricultural residues which are left on the soil in order to biodegrade. The main objective of this work is to valorise this vegetable matter for the production of pulps for papermaking. Several cooking processes and conditions were applied in order to cook banana crops and different cellulosic pulps were produced. It is interesting to note that the yield of chemical pulps reached about 40% and that the delignification time was very short, i e. less that 75 minutes for soda-anthraquinone and/or kraft cooking processes at about 120°C. The prepared pulps were characterised in terms of fibre morphology, drainage and physical, optical and mechanical properties. As in the case of pulps obtained from wheat straw, the pulps obtained from banana crops were found to contain a high amount of fines. Thus, about 60% of the fibres have a length lower than 0.5 mm. Hand sheet papers with a basis weight of 140 g/m2 were made and used for the preparation of corrugating. The properties of these papers and corrugated samples are summarised in table 1. From these data one can conclude that the properties of papers made from banana crops are, at least, as good as those of commercial samples. Some as the CMT or RCT are even higher.

3 - Pulps from Cynara cardunculus

Cardoon (Cynara cardunculus L.) is a plant growing in regions with severe climatic conditions and very low contents of water in the soils. This plant could be collected twice per year and it is presently cultivated in Spain and Portugal.

This plant was studied with the same aim as that of those mentioned above, i e. its valorisation as a source of lignocellulosic fibres. Soda-anthraquinone pulping was found to be the most suitable delignification process. The optimal conditions were established and showed that in two hours at 140°C about 38 % of chemical unbleached pulps could be obtained. The properties of these pulps were determined using commonly used standards, as summarised in [Table 1].

From these results, one can conclude that these pulps are suitable for the production of medium, since their properties were much better than those of commercially available products.

ln conclusion, these agricultural wastes could be used as a source of lignocellulosic fibres in order to produce flutings materials. This enables, at least, to partially replace recycled fibers used in the production of packaging materials.

  Fluting papers Steam-explosed
wheat straw pulps
Banana crops Cardoon
Shopper - Riegler °SR - 58 59 24
Basis weight (g/m2) 130 130 136 142
Bulk (cm3/g) 1.5- 1.6 1.3 1.06 1.3
Density (g/cm3) 0.67 - 0.62 0.77 0.94 0.77
Burst index (kPa.m2/g) 1.5 - 1.7 3.5 4.7 3.7
Tear index (mN.m2/g) 3.5 3.7 13.8 3.3
Elongation at break (%) 2.2 - 1.44 3.2
Breaking length (Km) 3.1 6.6 6.2 6.1
Zero-Span tensile (Km) 8 - - 9.2
RCT (N) 126 - 220 180
CMT (N) 160 - 230 225 301 252

Table 1 - Comparison of mechanical properties of unbleached pulps usually
used in the manufacture of fluting medium papers.

 
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