CHAPTER IV.
AN ACCOUNT OF THE CHEMICAL AND PHYSICAL CHARACTERISTICS OF THE PRINCIPAL RAW MATERIALS.
This chapter contains the results obtained from an investigation of the different plant fibres by the methods indicated in the two previous chapters.
In the following table the fibres are classified according to the reactions which they give with iodine solution.
CLASSIFICATION OF PLANT FIBRES ACCORDING TO THEIR COLOUR REACTION WITH IODINE SOLUTION (VÉTILLART).
A. B. C. Seed Hairs. Dicotyledonous Monocotyledonous Bast Fibres. Fibres corresponding to Bast Fibres.
Blue reaction Cotton. Linen. Straw. Hemp. Esparto. China grass. Pine apple. Paper mulberry Sunn. Yellow reaction Jute. New Zealand flax. Yucca. Hibiscus. Aloe. Manilla hemp.
Class A. COTTON.—Genus, _Gossypium_. Order, _Malvaceæ_. Seed hairs, consisting of ultimate fibres. Length, 2·0–4·0 c.m., diameter, 0·012–0·037 mm. Mean ratio, 1250. Illustrated in Fig. 5: _a_, sections; _b_, longitudinal views; _c_, ends; mag. 300.
Microscopic features.—Fibres simple, opaque, flattened, always more or less twisted upon itself, side wall membranous, showing striæ. {47}
Sections.—Simple, oval, irregular, central cavity often containing granules.
Micro-chemical reaction.—Blue with iodine solution.
General chemical characteristic.—Pure cellulose basis with slight admixture of colouring matters, &c.
COMPOSITION OF RAW FIBRE.
Church. Müller. Cellulose 91·15 91·35 Fat 0·51 0·40 Aqueous extract (containing nitrogeneous substances) 0·67 0·50 Water 7·56 7·00 Ash 0·11 0·12 Cuticular substance (by difference) .. 0·63
E. Schunck in his investigation of cotton bleaching (Chem. News, 17, p. 11) finds that in boiling with sodium carbonate solution the fibre loses 5 per cent. in weight. Some portion of the dissolved substances is precipitated on acidifying and is found to contain a wax, brown resinous and colouring matters, and pectic acid. {48}
Forms in which employed.—Fibrous refuse from the decortication of the seeds; spinning waste, threads, rags, new and old.
Class B. FLAX.—Genus, _Linum_. Order, _Linaceæ_, Bast fibres and filaments. Length of fibres, 25–30 mm.; diameter, 0·02 mm., ratio, 1200. Illustrated in Fig. 6: _a_, sections of the fibres, isolated and in groups; _b_, the fibres viewed longitudinally, one showing the creases produced by repeated bending; _c_, ends; _a′_, sections of fibres situated near the butt of the plant; mag. 300.
Microscopic features.—Fibres transparent, regular, with tapered ends, side walls thick, consequently central canal small, smooth externally, sometimes slightly striated. Filaments easily split up into fibres.
Sections.—Polygonal, regular, angles more or less acute, lumen represented by point; slight indications of concentric arrangement of fibre substance.
Micro-chemical reaction.—Blue with iodine solution.
General chemical characteristic.—Pecto-cellulose.
Composition of raw fibre.—This varies with the different species, and is doubtless also influenced by variations in the {49} processes of retting. The following are the analyses of two samples of Belgian flax (heckled):—
Müller. Cellulose 81·99 70·55 Fat and wax 2·37 2·34 Aqueous extract 3·62 5·94 Pectous substances 2·72 9·29 Water 8·60 10·56 Ash ·70 1·32
The chemistry of the flax fibre has been investigated by Kolb.
Forms in which employed.—Scutching refuse, spinning waste, threads, rags, new and old.
HEMP.—_Cannabis sativa._ Order, _Cannabinacæ_. Bast fibres: length, 22 mm.; diameter, 0·022 mm.; ratio, 1000. Illustrated in Fig. 7: _a_, _a′_, sections of groups of fibres of the first and second zone respectively; _b_, fibres seen longitudinally; _c_, ends; mag. 300.
Microscopic features.—Compact bundles. Fibres show striæ and fissures, and often fibrillæ, detached or adherent. The central canal almost obliterated, ends of fibres large and flattened. The bundles show fine transverse markings. {50}
Section.—Well marked concentric zones of fibre substance, irregular in outline.
Micro-chemical reaction.—Blue and yellow reaction with iodine solution, the joint result showing green colouration.
General chemical characteristic.—Pecto-cellulose.
COMPOSITION OF RAW FIBRE (ITALIAN HEMP).
Müller. Cellulose 77·13 Fat and wax ·55 Aqueous extract 3·45 Pectous substances 9·25 Water 8·80 Ash 0·82
Forms in which employed.—Scutching refuse, spinning waste, threads, cuttings and rope ends.
SUNDA or SUNN HEMP.—Genus, _Crotalaria_. Order, _Papilionaceæ_. Bast filaments: length, 7–8 mm.; diameter, 0·03; ratio, 200 : 1.
Microscopic features.—Generally similar to those of hemp.
Micro-chemical reactions.—With iodine various, from blue to yellow. With aniline sulphate, slight yellow.
General chemical characteristics.—Pecto-cellulose (with some ligno-cellulose).
The following are the results of analysis of the raw fibre (H. Müller):—
Cellulose 80·01 Fat and wax ·55 Aqueous extract 2·82 Pectous substances 6·41 Water 9·60 Ash 0·61
This fibre, exported from India and the Sunda Islands, has found employment in Spain and Portugal, but up to the present has not been adopted to any extent in other parts of Europe.
CHINA GRASS, RHEA, RAMIE.—Genus, _Bōhmeria_. Order, _Urticaceæ_. Bast filaments: length, 120 mm.; diameter, 0·05; ratio, 2400 : 1. Illustrated in Fig. 8: _a_, section of a {51} bundle of fibres; _b_, a fibre seen longitudinally; _c_, ends; mag. 300.
Microscopic characteristics.—Irregular in form and length; often conspicuous in respect of latter (see Table, p. 39); fibre sometimes cylindrical, either smooth or striated, sometimes flattened; central canal well developed, often containing granules; extremities of fibres rounded, spatulated or lance-shaped. Sections marked by numerous concentric layers, often showing radiating striæ.
Micro-chemical reaction.—Blue to violet, with iodine solution.
General chemical characteristics.—Pecto-cellulose.
Composition of raw fibre (H. Müller):—
Cellulose 75·83 62·50 Fat and wax ·20 0·56 Aqueous extract 6·29 9·76 Pectous substances 6·07 12·00 Water 8·74 9·55 Ash 2·87 5·63
Forms in which employed.—Up to the present the price has been prohibitive. Has been the subject of successful {52} experiments; imparts great tensile strength to paper. The portions available will be as in flax.
COMMON NETTLE.—_Urtica dioica._ Order, _Urticaceæ_. Bast filaments: length, 27 mm.; diameter, 0·05; ratio, 550. Microscopic characteristics similar to the above.
The fibres of this plant were, in the olden times, separated in the same way as flax, and worked up into cloth. At present it has no practical interest to the paper-maker, but deserves attention at the hand of the student, as the most easily accessible for the purpose of study. It is, moreover, possible that, under cultivation, it may yet become a source of raw material for paper-making.
JUTE.—_Corchorus._ Order, _Tiliaceæ_. Bast: length, 2 mm.; diameter, 0·022; ratio, 90. Illustrated in Fig. 9: _a_, section of bundles of fibres; _b_, fibres seen longitudinally; _c_, ends; mag. 300.
Microscopic features.—Compact bundles; fibres smooth.
Micro-chemical reactions.—Yellow brown, with iodine; yellow, with aniline sulphate; bright yellow, with chlorine water; changed to carmine by treatment with sodium sulphite solution. {53}
General chemical characteristic.—Ligno-cellulose. The chemistry of jute as the type of ligno-cellulose has been treated on p. 17.
Composition of raw fibre (Müller):—
Cuttings or Butts. 1st Quality. (Root ends). Cellulose 63·76 60·89 Fat and wax 0·38 ·44 Aqueous extract 1·00 3·89 Non-cellulose, or lignin 24·32 20·98 Water 9·86 12·40 Ash ·68 1·40
Forms in which employed.—Threads, butts, bagging.
BAST TISSUES.—We have alluded, in our opening remarks, to the broad division of the bast of exogen or dicotyledonous plants into coherent and non-coherent tissues. We have now considered the more important of the latter, and we find that they are obtained from the stems of annuals. We find also that while they constitute a tissue, in the sense of being definitely localised, the constituent fibres are disposed in parallel series of independent bundles or filaments, which are isolated by a mechanical operation after the whole stem has undergone the preparatory retting process. In exogens of longer and larger growth, the bast, as might be expected, becomes a coherent compound tissue, which is, in many cases, easily detached from the underlying wood. We shall mention three of these as receiving very important applications; though only one has been applied to any extent by the papermakers of this country. This, which we shall consider first, is the bast of the _Adansonia digitata_, or baobab, a tree which flourishes in the tropical regions of the West Coast of Africa. It is exported chiefly from Loanga, in the form of fibrous lumps of a brown colour. These are seen to be composed of a network of bast bundles, which are but slightly coloured, intersected by medullary rays of a dark brown colour. The microscopic features of the fibre are those which are generally characteristic of the bast of exogens; we do not know that we could cite any whereby it could be identified with certainty. {54}
The fibres give a yellow colouration with aniline sulphate, but they contain only a small proportion of lignose. The following are the results of analyses of this bast:—
Cellulose 49·35 58·82[7] Fat and wax 0·94 0·41 Aqueous extract 13·57 7·08 Pectous substances 19·05 15·19 Water 10·90 13·18 Ash 6·19 4·72
[Footnote 7: Made up of 13·75 cellulose from medullary tissue, 45·07 cellulose of fibres.]
_Linden Bast_ (_Tilia Europæa_) is the raw material employed in the manufacture in Russia of the mats so largely used in this country for wrapping furniture and heavy goods, and also by gardeners for a variety of purposes. One of the features of this bast is the strong cohesion of the fibres in the bundles or filaments. They are resolved, but with difficulty, on long boiling, with a solution of carbonate of soda, the soluble products being of a mucilaginous nature. This bast has not been applied to any extent by the paper-makers of this country.
_Bast of the Paper Mulberry_ (_Broussonetia papyrifera_).—This product deserves mention, not from its importance to the European papermaker, but because of its application to the manufacture of the peculiar papers of the Chinese and Japanese. The special features of this, and the other basts which are similarly employed in these countries—_Edgworthia papyrifera_, _Broussonetia kaempferia_, are (1), the ease with which the coherent fibrous tissue is separated from the parenchymatous tissue which accompanies it; (2), its comparative freedom from medullary rays; (3), the great length and fineness of the fibres. These properties conduce to its ready conversion into a well felted paper, of great tensile strength and remarkable softness.
Class C.—These are whole stems of monocotyledonous annuals. The isolation of fibres for paper-making from these plants depends upon a chemical process of resolution; the {55} pulp obtained is, therefore, a complex of the various orders of cell-fibres contained in the plant. While the pulp consists for the most part of the vessels of the fibro-vascular bundles, it contains in addition the serrated cuticular cells which are so characteristic of this group. They therefore present a general similarity in microscopic features; there are, however, certain individual characteristics, such as the form and dimensions of particular cells, which serve for the identification of the various pulps. Where such occur they will be indicated.
ESPARTO.—_Stipa tenacissima_ and _Lygeum Spartum_.
Order, _Gramineæ_. Bast fibres of fibro-vascular bundles. Length, 1·5 mm.; diameter, 0·012 mm.; ratio, 125. Illustrated in Figs. 10, 11. In Fig. 10, the fibro-vascular {56} bundles _f_ are seen spread throughout the interior of the leaf, but the intervals, instead of being occupied by parenchyma, with large cells and thin walls, are filled with a compact mass of fine solid fibres _f′_; _e_, external epidermis; _e′_, internal epidermis; mag. 100. In Fig. 11, _a_ is a section of a group of fibres; _b_, fibres seen longitudinally; _c_, ends; mag. 300.
Microscopic features.—Short, smooth, cylindrical, uniform in diameter, central canal very small, extremities rounded, truncated and bifurcated.
Section.—Minute, generally oval, sometimes polygonal; central cavity represented by a point.
Micro-chemical reaction.—Both blue and yellow with iodine solution.
In examining a paper containing esparto under the microscope, the pulp will be found to contain, in addition to the fibres of the fibro-vascular bundles, a certain number of the cuticular cells (see Fig. 12), together with some of the fine hairs which are seen in the section (Fig. 10). These are very characteristic.
General chemical characteristics.—Pecto-cellulose mixed with some ligno-cellulose. {57}
Composition (Hugo Müller):—
Spanish. African. Cellulose 48·25 45·80 Fat and wax 2·07 2·62 Aqueous extract 10·19 9·81 Pectous substances, &c. 26·39 29·30 Water 9·38 8·80 Ash 3·72 3·67
STRAW.—Order, _Gramineæ_.
Microscopic features.—Generally similar to those of esparto. There are, however, differences of shape and dimensions of the serrated cuticular cells, which differentiate the various kinds of straw from each other and from esparto.
In Fig. 12 are shown these cells, from maize-straw (_a_ and _b_); from rye-straw (_c_) and from esparto (_d_). The {58} following table gives the dimensions of the cells from different kinds of straw:—
Length. Breadth. Barley 0·103–0·224 mm. 0·012–0·014 mm. Rye 0·086–0·345 „ 0·012–0·016 „ Wheat 0·152–0·449 „ 0·018–0·024 „ Oats 0·186–0·448 „ 0·012–0·017 „
Another distinctive feature of straw-fibre is the presence in it of a number of oval cells, derived from the pithy matter attached to the inside of the stem. These are clearly shown at _b_ (Fig. 13), which represents the general appearance of straw pulp.
General chemical characteristics.—Both ligno-cellulose and pecto-cellulose.
The following are the results of analyses of straws (Hugo Müller):— {59}
Winter Wheat. Winter Rye. Cellulose 46·60 47·69 Fat and wax 1·49 1·93 Aqueous extract 8·07 0·05 Non-cellulose or lignin 28·49 26·75 Water 9·85 11·38 Ash 5·50 3·20
BAMBOO AND SUGAR CANE.—Order, _Gramineæ_.
From the close botanical relationship of these products to the stems of the gramineæ of our own climate, their microscopic features are, as might be expected, similar to those of straw. The similarity is further shown by the chemical composition (Hugo Müller):—
Air-dried Cellulose 50·13 Fat and wax ·78 Aqueous extract 10·56 Lignin and pectous substances 24·84 Water 8·56 Ash 5·13
NEW ZEALAND FLAX.—_Phormium tenax._ Order, _Lineaceæ_. Fibro-vascular bundles of the leaves.
Microscopic characteristics.—Length of fibres, 9 mm., diameter 0·016 mm., ratio, 560. Fibres are fine, regular and smooth; the walls are uniform, central canal small, extremities vesicular. The fibres have little cohesion in the bundle. Sections round or polygonal. Illustrated in Fig. 4, p. 35.
Micro-chemical reaction.—Yellow, with iodine solution. Characteristic deep red colouration with concentrated nitric acid (Müller).
General chemical characteristic.—Ligno-cellulose. It contains 86·3 per cent. of cellulose.
MANILLA HEMP.—_Musa textilis_, Abacá. Order, _Musaceæ_. Fibro-vascular bundles of leaves.
Microscopic characteristics.—Length of fibres, 6 mm.; diameter, ·024 mm.; ratio, 250. Fibres, white lustrous; the walls are uniform; central cavity large and very apparent. Fibres easily detached. {60}
Sections round or polygonal. Illustrated in Fig. 14: _a_, section of bundle of fibres; _b_, fibres seen longitudinally; _c_, ends; mag. 300.
Micro-chemical reaction.—Yellow with iodine solution.
Composition (Hugo Müller):—
Cellulose 64·07 Fat and wax ·62 Aqueous extract ·96 Lignin and pectous substances 21·60 Water 11·73 Ash 1·02
WOOD.—Nearly, if not the whole of the chemical wood pulp used in this country is obtained from trees belonging to the order _Coniferæ_ (Gymnospermæ), more particularly from the genera _Abies_ and _Pinus_.
In America, however, poplar and other woods are largely employed. The coniferæ yield a larger proportion of pulp than most other woods, the individual fibres, moreover, are longer, and for these reasons it is generally preferred. On the other hand, however, poplar is more readily acted upon by reagents. Fig. 15 gives the microscopic appearance of {61} the fibre of the common white fir. It is characterised by the presence of numerous pitted vessels (Fig. _a_).
Pine wood consists essentially of a compound cellulose, resembling in most of its properties the jute fibre (see p. 16). With iodine solution it gives a deep yellow colour. The chemical composition of some of the more important woods will be seen from the following analyses. (Müller.)
----------------+------+------+-----+-----+------- |Birch.|Beech.|Lime.|Pine.|Poplar. +------+------+-----+-----+------- Cellulose[8] | 55·52| 45·47|53·09|56·99| 62·77 Resin | 1·14| 0·41| 3·93| 0·97| 1·37 Aqueous extract | 2·65| 2·41| 3·56| 1·26| 2·88 Water | 12·48| 12·57|10·10|13·87| 12·10 Lignin | 28·21| 39·14|29·32|26·91| 20·88 ----------------+------+------+-----+-----+-------
[Footnote 8: For the amounts of cellulose actually obtained in practice see p. 77.]
The above results are calculated on the ash-free wood. The ash varies from about 0·3 to 0·7 per cent.
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