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AIR2-CT92-1796
Renewpack: Improved Packaging Products From Renewable Materials |
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Proposal No: | AIR2-CT92-1796 |
| Date Prepared: | September 1999 | |
| Source: | Final report October 1998 |
Summary
A major scientific endeavour for the Renewpack project has been to find a proper combination of agriculture- sourced, fibrous and renewable materials (FRM) with the best obtainable processing methods for pulping. Agriculture-sourced FRM includes waste such as straw. It also includes purpose-grown fibre crops such as miscanthus or hemp. Likewise included is rotation wood such as coppices or farmed poplar. Coppiced eucalyptus is another species suited to fibre-farming in short rotation, but only if suitable growth sites can be found. If wood is considered, production should fit into the farm production system for crops like miscanthus.
The Renewpack project concerns paper- and paperboard-based packaging. It focusses on case-making materials (corrugated and solid board boxes) and on moulded forms. A secondary objective has been to achieve a degree of moisture-resistance in packaging materials using compounds obtained from spent pulping liquor or other natural polymer material. The research activities have been divided into four areas as follows.
Pulp and paper technology The key observation arising from the pulping studies was that no combination of FRM/pulping method was capable of producing a pulp which met all the criteria laid down by the industrial partner for viable reinforcing pulps. This was true for both fluting and testliner media. The poor performance of all pulps with respect to WRV was cited by the industrial partner as a particular cause for concern. The fact that even the reference raw materials - birch and mixed hardwoods - when pulped to 80% yield using the conventional NSSC process, did not meet the pulp property criteria is indicative of the extremely demanding requirements laid down by industry. It was evident from some additional studies that the strength properties of birch NSSC pulps could be increased by pulping to lower yields (75%), such that they exceeded the requirements for fluting laid down by the industrial partner. However, these pulps still did not meet the WRV requirements and it is uncertain whether pulping to such yields would be economically viable. Given this, it is questionable whether the pulp property criteria laid down by the industrial partner are in fact realistic.
Barrier technology Extrusion pulping in combination with alternative fibre sources may be seen as viable competition to classical pulping routes, whereas for the production of coating or impregnation substances based on hemicellulose, the results so far do not appear to be very promising. As the experimental deficiencies observed in this project may be overcome in the future, this statement is by no means an absolute one.
Market and economics The trend towards a reduction in the volume and weight of packaging stimulates re-use and recycling of packaging. This has a significant consequence for the use of packaging materials. Packaging in the EU is moving away from paper with virgin pulp to a wastepaper-based material. Testliner increasingly replaces kraftliner and semi-chemical fluting from virgin pulp. The general search to reduce the weight of packaging material and minimise cost involves a reduction in the material used or a substitution with less-costly material. Furthermore, legislation will encourage returnable and re-usable packaging, recycling of material and the use of biodegradable packaging.
Environmental issues From the comparison of the three types of non-coated corrugated board - the gross energy input from non-renewable sources and the global warming potential - shows values that are similar within the usual span of uncertainties. Extrusion pulping of alternative fibre sources seems therefore to be equivalent to conventional pulping routes from an environmental point of view.
In effect, the process of peroxide bleaching is the predominant factor of environmental relevance in the coating/impregnation step. Thus any technique which is able to avoid this step will lead to better figures. Whether the improvement would again balance out due to lower paper-input can only be stated after the complete description of a newly-developed process. Therefore, the answer to the question whether coating/impregnation substances derived from by-products of alternative pulping routes may have an overall beneficial or negative environmental impact cannot be answered by the work done in this project.
Objective
The overall objective of the Renewpack project was to improve packaging products - for favourable quality and favourable environmental performance - manufactured from recycled and renewable paper-based and paperboard-based sheet material.
For favourable quality, improved packaging materials and products would be defined as showing:
Favourable environmental performance was to be explored in terms of:
Activities
The research was divided into four parts.
Pulp and paper technology The key observation was that no combination of FRM / pulping method was capable of producing a pulp which met all the criteria laid down by the industrial partner for viable reinforcing pulps. This was true for both fluting and testliner media. The poor performance of all pulps with respect to WRV was cited by the industrial partner as a particular cause for concern. The fact that even the reference raw materials (birch and mixed hardwoods), when pulped using the conventional NSSC process to 80% yield, did not meet the pulp property criteria is indicative of the extremely demanding requirements laid down by the industrial partner in the project. It was evident from some additional studies that the strength properties of birch NSSC pulps could be increased by pulping to lower yields (75%), such that they exceeded the requirements for fluting laid down by the industrial partner. However, these pulps still did not meet the WRV requirements and it is uncertain whether pulping to such yields would be economically viable. Given this, it is questionable whether the pulp property criteria laid down by the industrial partner are in fact realistic.
Despite the failure of all FRM / pulping process combinations to meet required target levels, the results of the study were nevertheless generally encouraging. In a number of cases experimental pulps came within 5-10% of the target levels for key properties. This was particularly true for poplar and miscanthus carbonate pulps, processed via the conventional semi-chemical route and targeted as reinforcing pulps for a fluting medium. The blending studies confirmed that optimised pulps from these FRMs - pulped to yields of around 80% - could significantly (p<0.05) improve the properties of the reference OCC pulp.
At the 30% level of substitution, OCC pulps showed approximately-proportional improvements in both breaking length and CMT 30 properties. The reinforcing potential of extruded miscanthus and wheat straw pulps was promising, showing similar levels of improvement in properties. Lower-yield wheat and rye straw pulps also showed similar reinforcing potential, though whether such pulps would be economically-viable to produce is questionable. Hemp pulps clearly demonstrated their potential for improving tear properties, though this was offset to some extent by the relatively poor performance of such pulps with respect to breaking length. Hemp fibre pulped via the extrusion route easily met the tear strength requirements for reinforcement of testliner pulps. However, it was also evident that such pulps fell considerably short of breaking-length requirements, in particular at the stipulated pulp freeness. It was found that breaking length could be significantly improved by using higher concentrations of carbonate reagent or higher shear levels in the extruder, or simply by beating the pulps for longer. However, all these approaches tended to increase significantly the SR freeness of the pulps, and a relatively low SR freeness was a key requirement of such pulps.
The necessity for putting more chemical and/or mechanical energy into the pulps in order to improve tensile pulp properties is a reflection of the fibre morphology and the composition of hemp fibres. Such fibres are high in cellulose-content and commonly have small (or sometimes no) lumens. As such they do not flatten readily and bonding between them can be relatively poor. It should also be noted that the hemp pulps were extremely difficult to evaluate:their excessive fibre length caused considerable problems during both the pulp-beating and handsheet-forming stages of the pulp-evaluation operation. It can be safely assumed that such pulps would not be considered for use on a commercial testliner-paper making machine. The only possible option would be to pre-cut the raw material to extremely short lengths. However, such an approach might seriously compromise the tear strengths of the resulting pulps. The one advantage that extrusion pulping might offer is that there was some evidence that the resulting pulps had slightly lower water-retention values compared with disc-refined pulps.
Whilst the pulps still failed to meet the criteria laid down by the industrial partner, this might be an advantage. However, the industrial partner cited the high WRV properties of all experimental pulps as being a major drawback for the likely acceptance of such pulps by the industry. If this truly is the case, then penetration into this market by novel FRM semi-chemical pulps could be extremely difficult, since there is little scope to significantly reduce WRV without compromising significantly on pulp yield.
The issue of whether either of the process routes investigated in this work might be economically viable is still very much open to question. The crucial steps in both processes are the pulp-yield and wash-water requirements, and the energy-generation / pulping chemical-recovery process. It was demonstrated that pulps with promising properties could be generated from poplar and miscanthus at realistic pulp yields. It is also known that mills in the United States are successfully running stand-alone recovery processes on carbonate-based semi-chemical pulping digesters for the processing of wood. However, it was extremely difficult to estimate on a laboratory scale what the pulp wash-water requirements were likely to be on a full industrial scale. This is absolutely vital information, since the wash-water requirements directly influence the energy required to evaporate excess water in order to reduce the effluent to a suitable solids-content, for combustion in the recovery boiler. Some crude experiments were conducted to estimate wash-water requirements for cooked and disc-refined poplar. It was apparent that some 35% more water was required to wash poplar compared with mixed hardwoods. Whether this is a true reflection of likely additional water requirements for poplar - and whether this has a significant impact on commercial viability - is unclear. It should be noted that it was always the original intention in the project to derive this critical information from pilot-scale pulping studies. However, these studies were dropped from the original work programme when it became evident that none of the experimental pulps met the property requirements of the industrial partner.
In summary, it is evident that whilst the experimental pulps produced in this work did not meet the proper requirements of the industrial partner, nevertheless some promising pulps were generated from both poplar and miscanthus using carbonate pulping reagents. Both disc refining and extrusion appeared to be appropriate methods for breaking down cooked material. These pulps had far superior strength properties to the OCC currently used to produce fluting, and it was demonstrated that they could be blended with the OCC pulp to impart significant property improvements. The major drawback with all the experimental pulps was their relatively high WRV; it is believed that this fact alone could seriously reduce the likelihood of such pulps being considered for fluting media due to the increased energy and reduced output considerations.
Barrier technology Overall the results indicated the following.
Market and economics Over the years, wastepaper-based testliner has gained market share in corrugated board from kraftliner as it is more competitive and cheaper to make, although on average it has a lower performance. In principle, kraftliner remains the best paper in very humid conditions, although testliner also becomes an increasingly-reasonable alternative in humid conditions. Until recently cost had been the driving force for this change, which had caused the conversion to testliner to be more pronounced in Europe than in North America. Over the last few years environmental concerns have meant that in Europe 70% of the paper used in corrugated cases is now wastepaper -based, and this figure will increase. Kraftliner supply from North America has dried up following increased domestic demand. The kraftliner manufacturers in the United States export only a small percentage of their home production. Unfortunately paper recovery is still seen by the general public and many governments as a waste-disposal problem, while recycled fibre is still widely perceived by paper manufacturers as a resource which offers a useful and viable, lower-cost alternative to virgin fibre pulp.
It is forecast that global paper recovery levels could grow by more than 60% to around 190 million tons by the year 2005. This would add over 70 million tons per year to worldwide recovery activity.
The principal customers of the packaging industry are manufacturers of chemicals and industrial products, food processors and beverage companies. Packaging companies have been faced with strong internationalisation of their customers and changing purchasing patterns. Large multinationals are starting to source their packaging needs for the whole of Europe from only one or two suppliers. Therefore, packaging companies are also forced to become international. In the packaging sector such international presence has been obtained by alliances or takeovers within Europe, with customers looking for further optimisation and standardisation of their packaging so that these costs can be reduced.
The global use of recycled fibre is increasing, especially in countries that produce paper, since wastepaper-based pulp is frequently seen as a lower-cost alternative to virgin pulp. There are related issues concerning shipping distances on costs for both virgin and secondary fibre, as well as the fact that installation of a secondary fibre pulp line often costs much less than the construction of a pulp mill. Secondary fibre also offers greater flexibility in terms of break-even production volumes and plant viability, because more-modest incremental expansions of paper- and board- making capacities are possible with recovered paper-based units than with the virgin fibre-based machines. The second reason is the growing worldwide issue of legislative and other regulatory influences on recovered-paper demand. This typically influences the secondary fibre sector from one or both sides of the supply-and-demand equation. In Europe for example, regulations concerning the recovery and recycling of packaging waste (much of which is paper-based) are enforced through the concept of "producer responsibility".
Environmental issues As far as energy is concerned, combinations of different process structures and the partitioning methods used are very significant. Whereas there are virtually no additionally-usable renewable sources in excess of the input fibres for recycled paper, there is a part of the wood (bark) that is used for energy-generation for wood fibres, thus giving a substitution effect of fossil vs. renewable energy in this part. For the alternative fibre sources investigated in this project, the amount of residues with a high heating value is remarkable. This would lead to the necessity to install in-house energy-generation schemes that would be able to deliver a substantial surplus of energy into the public grid.
According to our model this gives an energy credit in relation to the final product and therefore a formally-negative energy requirement on the renewable energy input side. This difference is therefore not a fundamental one but strongly-dependent on the boundary conditions of the system under study. In the non-renewable energy figure the three basic systems are similar. This figure therefore mainly reflects the fossil energy needed for the processes.
The differences in mineral requirements only reflect the still-not-perfect modelling of the experimental process from experimental data, rather than a general feature of the renewable fibre sources.
The water input is lowest for the recycled paper production, a known effect due to the different processes; for the two different sources of virgin fibres, there is no real difference. It has to be noted, however, that a slightly-positive influence results from the extrusion-pulping process modelled for hemp. This, however, must be proven in a later large-scale application with an appropriately-realised process layout.
The differences in municipal type of waste are also not largely different in view of the uncertainties valid for the assumptions in process modelling.
The largest difference is to be observed in chemical waste, where the new pulping routes apparently show a prominent figure. This is however not due to the pulping process but again, rather to the in-house power generation by residual biomass, which in this case points in another direction. The relatively-high amount of incinerated biomass leads to higher production of filter dust from exhaust air cleaning, which is classified as chemical waste.
Radioactive waste correlates 100 % with the amount of electricity needed in the process, given by the fraction of nuclear energy in the specific grids. The predominant occurrence of this parameter for the conventional virgin fibre pulping is simply due to the fact that Sweden has a higher fraction of nuclear energy in its national grid compared to the European average. Also, the values for eutrophication and acidification are in the same order of magnitude.
Closest together are the values for global warming, in concert with the fact that this value can be established relatively efficiently because the overall carbon balance can be checked and adjusted. The ozone-depletion potential, finally, is not often quantifiable for individual process outputs, as the output quantities of the related substances are not always measured. In our case the only quantifiable origin of substances related to this category is the production process of caustic soda according to new BUWAL data. Here, the surplus for the alternative fibre source is basically due to its higher requirement for caustic soda, a true speciality of the experimental process.
Alternative pulsing routes The comparison of the three types of non-coated corrugated board, the gross energy input from non-renewable sources and the global warming potential - used as the most important indicators - shows values that are similar within the usual span of uncertainties. Extrusion pulping of alternative fibre sources seems therefore to be equivalent to conventional pulping routes from an environmental point of view. Here the comparison of impregnated material with the non-impregnated counterpart always shows an environmental disadvantage for the former. In spite of the assumed high improvement factors - which lead to related input reduction in fibrous materials - the extra effort for producing the modified hemicellulose as impregnation substance outweighs this benefit by far.
As an effect, the single process of peroxide bleaching is the predominant factor in the environmental relevance of the coating/impregnation step. Thus any technique which is able to avoid this step will lead to better figures. Whether these would again balance out the improvement due to lower paper input can only be stated after a complete description of a newly-developed process. Therefore, the answer to the question of whether coating/impregnation substances derived from by-products of alternative pulping routes may have an overall beneficial or negative environmental impact cannot be answered by the work done in this project.
Conclusions
Extrusion pulping in combination with alternative fibre sources may be seen as a viable competition to classical pulping routes, whereas for the production of hemicellulose-based coating and impregnation substances, the results so far do not appear to be very promising. This statement is by no means an absolute one, as the experimental deficiencies observed in this project may be overcome in the future.
© Copyright 2006 Policy Statements
Updated
by CPL Press:
03/07/2007
- biomatnet@biomatnet.org
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