F.H. Phillips
F.H. Phillips is a Principal Research Scientist in the Division of Chemical and Wood Technology of the Commonwealth Scientific and Industrial Research Organization (CSIRO). Clayton, Victoria, Australia. This article has been adapted from a paper presented by Mr Phillips at the May 1983 International Symposium on Wood and Pulping Chemistry in Tsukuba Science City, Japan.
In the history of resources used in the pulping process, the dominant feature is change. Yet, paradoxically, the pulp and paper industry today is reacting much too slowly in adopting new pulping resources. There is now considerable evidence to show that resources whose potential had previously been disregarded, particularly eucalypt species and certain agricultural residues, have a bright future.
· The raw materials used for commercial pulping and paper-making have changed greatly over the years, but changes are still occurring, and the potential value of new materials must be adequately evaluated in order to utilize fibre resources efficiently. An adequate evaluation of pulping and paper-making quality must include inventory preparation, sample collection and evaluation, and comparison with established materials. Tropical forests are becoming increasingly important for new fibre resources and require particular attention.
In general, the pulp and paper industry has been slow to take advantage of resources that are different from traditional materials. Nevertheless, as supplies of preferred raw materials have diminished or as consumption of products has increased, changes in the raw materials used in the industry have occurred. This trend will continue, and a greater variety of materials will require processing to meet industry requirements.
STACKED BAGASSE IN CUBA: new importance as a pulping resource
CUTTING SUGAR CANE IN CUBA: afterwards, the bagasse becomes paper
There is a strong argument for greater cooperation between countries in matters concerned with the utilization of forest and non-wood resources available for pulping and paper-making. Greater technical expertise must be acquired, and the possibility of local industries in whole regions must be investigated seriously, irrespective of possible political difficulties. Scientists and technologists, aware of the need to use resources more efficiently, have developed new ways of incorporating increasing quantities of waste wood and residue materials in the pulpwood furnish.
Comparatively little use is at present being made of materials that can be grown as annual crops or of agricultural residues and other, similar fibre sources, many of which are often readily available. Before pulpwood was used, agricultural materials and residues played an important role in the paper industry and often yielded high-quality products. Such resources today are almost always utilized exclusively in small-scale operations. Recently, however, the use of reeds - or rather "eta reeds", a mixture of Ochlandra species which are bamboos and not, strictly speaking, reeds - as a source of long-fibre pulp for newsprint has been explored in India, the production of premium-grade pulp from abaca fibre has been undertaken in the Philippines, and an industry has been established in Thailand for the production of pulp from kenaf. Together with bagasse and straw, such materials could become important in future operations.
Techniques used in converting the bark of the papyrus reed, animal skins or beaten bamboo stems to handmade sheets for writing material were quite different from those developed later for the conversion of linen and cotton rags, flax and other fibrous vegetable materials. A later step, which opened the way for cheaper, large-scale operations, was the development of techniques for the separation of cellulose fibres from wood by means of both mechanical and chemical processes.
These examples illustrate the fact that it is both necessary and possible to adapt production methods to fit the available raw material. As the pulp and paper industry developed, however, there was a tendency to consider coniferous woods the only satisfactory material for producing high-quality papers suitable for a variety of end-products. Both manufacturing techniques and product specifications were tailored to fit conifers. Industries in developed countries now accept the importance of short-fibred materials and the need to utilize mill waste, forest residues and young unbarked thinnings as economically necessary and environmentally desirable; but they should also be prepared to use increasing quantities of bagasse, straw, kenaf and similar materials if these are available in sufficient quantities.
Pulping the eucalypts. It is well known that Australian eucalypts were originally considered unsuitable for pulp production. The long investigations into these eucalypts which led to the commercial production of groundwood pulp for newsprint, soda pulp for writing and printing papers, and kraft pulp for packaging papers - have been well documented (Benjamin, 1959). As often happens with "new" materials, attempts to pulp the wood in the same way as for coniferous species produced an unacceptable pulp, low in yield and poor in quality. Pulping processes had to be modified to suit the specific properties of the new raw material before it became possible to use the eucalypts commercially.
Although the quality of pulp obtained from eucalypts was not the same as that from traditional materials, eucalypt pulps, when used in a mixture with other pulps, have become the basis for an extensive range of products (Higgins, 1970). Methods employed include the use of mixed fibrous furnishes to meet production schedules and quality specifications, and the development of new types of pulp to improve quality and to reduce dependence on imports. One can cite, for example, the fibrous furnish of some grades of wrapping paper: about 70 percent eucalypt kraft, beaten to a low freeness to develop bonding strengths, and about 30 percent long-fibre pulp, lightly beaten to retain tearing resistance. Another example is newsprint, which in Australia was initially made from eucalypt groundwood and some imported long-fibred kraft pulp but is now produced from a mixture of groundwood and cold-soda semi-chemical pulps from eucalypts and thermomechanical and kraft pulps from radiate pine.
Of the many eucalypt species available, only a limited number are currently used for pulping.
It could not have been predicted even a few decades ago that the application of the neutral sulphite semi-chemical (NSSC) process to overmature eucalypts would give such an excellent pulp for corrugating medium. Neither could it have been predicted that NSSC pulp from regrowth eucalypts, obtained in over 60 percent yield, could be used as a replacement for kraft pulp in kraft liner board and other products.
Most authorities now acknowledge the value of hardwood pulps, such as those derived from eucalypts, in the furnish of writings and printings that give the surface properties desired by printers. Even in the United States, a marked increase in hardwood utilization for pulping has occurred. Before 1950, hardwoods contributed less than 15 percent of total US pulpwood production, but this figure had increased to 26 percent by 1979 (McGovern, 1981). A large increase in the use of hardwoods for pulping has also been evident in the Japanese economy. According to figures published by the Japan Paper Association (1982), 36 percent of the volume of the total pulpwood consumed in 1960 was hardwood, whereas by 1980 the industry was using 50 percent hardwood.
The development of the Australian pulping industry, which was based on eucalypt pulpwood resources, uncovered some unique problems: sticking at the press occurred with eucalypt kraft pulps (Jeffreys, 1947; Farmer, 1949); extractives such as ellagic acid affected the evaporation and burning characteristics of black liquors (Hillis and Carle, 1959; Baklein, 1960); and tannins in mature eucalypts caused discoloration of groundwood pulps (Lethlean, 1949; Neale et al., 1949; Tardif, 1959). These were only a few of the difficulties that were encountered and overcome, and many different problems can be expected with other new fibre resources.
However, because of certain inherent properties, the utilization of the eucalypts for pulping has also brought advantages to the industry: the reduced need for chemicals in pulping; more efficient use of digester capacity; faster development of pulp strength on beating; and the production of papers with better formation, smoother surface and higher opacity and of boards with better crush resistance.
Other advances achieved by the industry include the modified application of the cold-soda process for the production of pulp from non-grindable eucalypts (Somerville and Pearson, 1958); the production of groundwood from impregnated billets (Elder et al., 1967); and the application of wet-air oxidation for pulp-mill chemical recovery (Morgan and Saul, 1968). Many of these and other developments have been documented by Watson (1969) in an informative article on the pulping of eucalypts in several countries.
There is an important aspect of eucalypt pulpwood utilization that is often overlooked. Of the many eucalypt species available, only a limited number are currently used for pulping, and their properties vary greatly both within and between species. Thus, it is not possible to be too specific about the pulping and paper-making potential of eucalypts without some knowledge of the physical and chemical properties of the material or of actual pulping data.
Tropical hardwoods for pulping. Like those of eucalypts, the properties of tropical hardwoods vary between species and under different growing conditions. There is a large number of species in the tropical hardwood forests, and the timber resources available in different tropical areas vary greatly.
AUSTRALIAN EUCALYPTS gathering respect as a pulping resource
It has been shown that kraft pulps with adequate strength properties can be produced from the mixture of hardwood species available in tropical forests and that high-brightness bleached pulps can be obtained without segregation of species (Logan and Phillips, 1975; Phillips and Logan, 1977; Phillips et al., 1975, 1979). Furthermore, production of neutral sulphite semi-chemical pulps suitable for corrugating medium and higher-grade products such as kraft liner board is possible (Phillips and Logan, 1977). Satisfactory NSSC pulp production cannot be achieved in a short-cycle digestion with a chemical charge which would, for example, be suitable for pulping Japanese domestic hardwoods. If such a procedure is applied, a high-kappa-number pulp with an unacceptably large quantity of screening rejects is obtained. But a satisfactory pulp can be obtained under more severe conditions of temperature and time and with a larger chemical addition. Of course, a lower pulp yield must be accepted.
Studies have also shown that many young, fast-growing tropical hardwood species produce kraft pulps with extremely satisfactory properties, including high strength. However, many of the same species are less suitable for high-yield pulps such as chemithermomechanical and cold-soda semi-chemical pulps (Phillips et al., 1980; Logan, 1981).
Non-wood resources. Because nonwood resources in pulping and paper-making operations behave differently from more commonly used materials, technologists in developed countries often underestimate their potential value. Innovation based on a technical knowledge of the properties of the raw materials is needed. This matter will not be discussed here in any detail, but some recent developments can be briefly highlighted:
· The establishment of a mill in Thailand for the production of 70000 tonnes per year of pulp from kenaf (Niyomwan, 1980).· The use of bagasse for mechanical and chemical pulp production of newsprint in a process which includes microbially controlled fermentation to inhibit deterioration of the bagasse in bulk storage (Aguero-Torres, 1980).
· Proposals for the briquetting of surplus sugar-cane bagasse to form a denser product more suitable for transportation and possibly for export as a pulp and paper feedstock (Rawlins et al., 1982).
· The development of a machine for continuous extraction of abaca fibres with a fibre yield 50-60 percent higher than that obtained from other extraction processes (Tamolang and Escolano, 1980).
· The application of an explosion technique for the preparation of pulps of a kappa number lower than 30 from pre-impregnated kenaf bark and wood, rice straw, wheat straw or bagasse, offering a rapid method of production from fast-growing and annual plants (Mamers et al., 1979).
Recently it has been emphasized that our bias against non-wood resources should be reconsidered. If materials such as straw, kenaf or bagasse can only be used economically on a small scale, there is a strong argument for modifying accepted mill operations to suit nonwood resources. This procedure is preferable to condemning these raw materials as unsuitable and using other, more expensive, possibly scarce fibre resources in large-scale operations.
The major considerations in the assessment of pulpwood quality have been described in some detail by Higgins and Phillips (1973), Phillips and Harries (1975) and Balodis (1980). Any potential resource must first be defined, preferably by inventory, and the material for pulping chosen. In commercial, integrated operations, the material for pulping will generally be the wood remaining after removal of the more valuable saw-logs and veneer logs. It may include small trees, noncommercial species, defective trees or portions of trees, forest residues and mill waste. When the quantity of material is established, serious consideration must be given to the types of product required and to whether sufficient pulpwood is available for the proposed end-use. None of the subsequent, costly procedures should be started until this estimate has been made.
Once the composition is established, a sample must be collected for testing. The sampling techniques adopted should aim at providing the best representative sample at the minimum cost. Random sampling is inefficient because it involves the collection of more trees than necessary. Balodis and James (1980) have shown that for a natural forest even a large random sample will not ensure that the various species and size classes are included in the correct proportions. Sampling efficiency can be achieved by stratification, which also involves consideration of the material in relation to the cost of sampling (Balodis, 1980). The number of trees to be sampled in each stratum - for example, in each diameter class - should be proportional to the volume represented by the stratum in the resource and inversely proportional to the sampling cost per tree.
Using data for commercial-size temperate hardwoods, Balodis has shown that the gain in precision of pulp yield, one of the most important pulping properties, diminishes rapidly after 15-20 trees. Thus, if four diameter classes are sampled from a species, five trees per class should be adequate. Furthermore, the optimum number of sample billets per tree depends on the coefficient of the variation of mean pulp yield, the sampling costs and tree size. Balodis (1980) has stated that in areas of high transport cost, sampling efficiency is maximized by taking a single wood sample from a random position in a tree, while in easily accessible areas it may be justifiable to take two or three samples from larger trees.
Just as necessary as the procedures for collecting samples are the decisions on how they will be evaluated. These take into account future utilization patterns involving the possible use of single species or alternatively of species mixtures; the type of pulping process to be employed; and the nature of the end-products required. Too often, single-species tests, including an elaborate determination of all possible physical and chemical characteristics, are made on samples from single trees from a forest resource that can only be used as a mixture of species. If end-use requirements cannot be defined, a wide range of sample types and pulping processes must be employed to provide evidence of quality for future decisions on resource management and end-use possibilities.
In the laboratory, a variety of wood-chip mixtures can be prepared from a well-planned and well-executed sample collection to represent a number of possible commercial utilization patterns. Unless the resource is dedicated to a particular process, a range of chemical, semi-chemical and mechanical pulping tests should be carried out here. Morphological and chemical analyses should be done, even on individual major species occurring in mixed-species pulpwoods, as an aid to improved utilization. Such knowledge may assist in the identification and possible separation of troublesome species. However, the pulping of a sample representing the mixture to be used commercially must be given first priority in any assessment of a resource containing a variety of species. Once the pulping and paper-making properties of the new fibre resources are determined, a comparison with laboratory-prepared pulps from commercially acceptable pulpwood materials will provide the best assessment of their potential uses.
At the laboratory level. The efficient utilization of eucalypts for pulping in Australia and elsewhere has necessitated the evaluation of the pulping properties of various species, recognition of the differences between eucalypt pulps and previously accepted pulpwoods, and the establishment of procedures to suit the different materials. The use of imported Australian eucalypt wood chips, for example, was more successful in some Japanese mills than in others. Generally, success appeared to be related to the acceptance of the fact that the new pulpwood was different from the Japanese domestic hardwoods normally used and that new equipment or revised operating schedules were required to meet the changed circumstances.
The same concept is needed to achieve efficient utilization of tropical hardwoods and other new fibre resources. In a mixed-species tropical forest, many species are acknowledged to be unsuitable for pulping. They may, for example, be too high in extractives, too dense for liquor penetration or too dark in color. Segregation of such trees can be difficult and uneconomic. Utilization of the total mixture of species resulting from a clear-felling operation could be the most reasonable pattern for the logging, chipping and pulping stages. Therefore, evaluation of the new resources must be carried out on samples that represent a realistic pulpwood mixture available for future pulping ventures.
The pulp and paper industry has been slow to take advantage of resources that are different from traditional materials.
Research into the chemistry of pulping and bleaching is essential for the efficient utilization of fibre resources.
Two examples from recent CSIRO studies on tropical hardwood resources illustrate this point. First, in one particular timber area of Papua New Guinea, 566 pulpwood samples, representing 106 genera and various diameter classes from 15 to 50 cm and above, were collected for the preparation of composite mixtures for pulping tests. Pulping and paper-making results showed that the representative mixture was suitable for making a wide range of products (Phillips et al., 1975). However, data on the 10 genera present in the highest proportion, which accounted for about 50 percent of the volume of wood, indicated appreciable differences in pulping properties between each genus. Basic density ranged from 261 to 757 kg/m3, and some species were quite unsuitable for individual use in pulping and paper-making for several reasons, including low yield, high alkali requirement and poor paper-making properties (Logan et al., 1978).
Second, in Sarawak, Malaysia, considerable quantities of Shorea albida from various sources were made available for chipping. The sample, prepared in correct proportion by volume for pulp evaluation studies, included stem-wood unsuitable for commercial use, off-cuts from sawmills and crowns from forest residues. Furthermore, the two varieties of the timber, alan batu (high density) and alan bunga (low-to-medium density), were also correctly represented according to estimates of availability (Phillips et al., 1979). The necessity for elaborate sample preparations was confirmed when the differences in the properties of the various components in the mixture proposed for commercial use were considered. The basic densities of the components ranged from 482 to 624 kg/m3 and the alkali requirements for pulping each component varied markedly. The pulping and paper-making results showed that an incorrect assessment of pulping potential would have been obtained if an individual component rather than a sample fully representative of the available material had been used in the assessment (Logan et al., 1977).
For many new resources, various options must be studied to assist the efficient future use of each. This requirement is illustrated by examples from recent pulping studies at CSIRO on Papua New Guinea resources (Logan and Phillips, 1975; Phillips et al., 1975). Numerous wood-chip mixtures were prepared, representing a clear-felling regime in the timber area; the species composition in different forest types; and the pulpwood mixture, excluding portions of large trees of some species required for saw-milling. It should now be possible to arrange future logging operations more efficiently for the following reasons.
· Even though there were differences in the wood resources for different blocks in the timber area - especially with regard to forest type, diameter class and species composition - the pulp properties were not greatly different.· The exclusion of large trees of some species for saw-milling or of small trees, or the exclusive use of hill or lowland species, had little effect on pulp quality.
· The large number of species in the mixture did not create problems, and segregation of species was not necessary for the production of high-brightness bleached pulp.
The principal factors affecting utilization will vary in each situation. The basis of the assessment to determine the suitability of the resource should be considered carefully before either the costly sample collection or the laboratory or pilot-scale evaluation stage is commenced. Furthermore, if alternative resources are available, the possibility of using these in combination should also be examined.
At the industrial level. The feasibility of importing wood chips on a large scale has been proved. Since several countries will face a shortage of local pulpwood in the foreseeable future, the practice of importing wood chips could become a pattern for these countries, including those that have been net exporters of forest products in the past. On the other hand, some countries may want to establish a pulping industry although lacking sufficient local fibre resources. Whether the import of wood chips is the most suitable procedure must be carefully considered along with other options. Adequate supplies of alternative materials, including non-wood resources, for example, could be available locally and permit the establishment of small-scale pulping operations. Small-scale development may be economically and socially more acceptable than the importing of material for a large-scale mill in a country with a large labour force, a low-wage structure and the possibility of tariff protection and other incentives. Furthermore, many non-wood fibre resources are relatively easy to cook, simple equipment may be adequate, and chemical recovery may not be required.
LEARNING HOW TO PLANT EUCALYPTS: a multi-purpose tree for a more diverse future
These advantages, together with the use of slower second-hand paper machines which are simple to operate and maintain, could result in a suitable pattern for development. Many of these points were outlined in papers presented at a recent meeting of international experts in Manila by Benzinger and Opderbeck (1980); Hackl (1980); Kalyanasundaram (1980); and Keswani (1980).
Research into the chemistry of pulping and bleaching is essential for the efficient utilization of fibre resources in pulping and paper-making. However, there are associated problems of equal importance which are often given insufficient attention. These include the need for an adequate inventory of the resource, including an assessment of whether sufficient material is available for the intended development; for an adequate and efficient sampling programme to collect material for subsequent studies; for a thorough evaluation of the available raw material to assess the pulping and paper-making potential; for an efficient utilization of each material, either individually or in combination, rather than mere substitution of the "new" materials in an existing process without modification; and for the assumption of responsibility for guiding development to the stage and scale desirable to ensure that the environment is protected and that all operations are carried out in the best interests and for the future benefit of the local people.
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