Báo cáo khoa học nông nghiệp " Processing, preservation and using wood of plantation forests " potx

1 Report for CFM Workshop ********** Project Code 027/06 VIE Improving operator skills and technology for small rural sawmills Processing, preservation and using wood of plantation forests Philip Blackwell: University of Melbourne, AVI and FSIV Pham Duc Chien: FSIV Sawmilling overview The sawmilling industry in Vietnam is made up of a number of small enterprises who saw available species and some large manufacturers who saw imported or specially species. They all use similar equipment, with the majority using a Vietnamese manufactured horizontal bandsaw mill. A few manufacturers have vertical bandsaws. The differences in the two machines other the direction of the cut is the vertical machines are stationary and the logs are moved past the blade while the horizontal mills are on a carriage which in pushed over the stationary log. Both methods produce a board the width of the log. This method is called flat sawing. Most of the boards are back-sawn (timber sawn so that the growth rings are inclined at less than 45 degrees to the wide face) while a few towards the centre of the log are quarter sawn. Quarter sawing (the average inclination of the growth rings to the wide face is not less than 45 degrees) is the most suitable method of sawing for species that have drying problems or are prone to movement in-service. Following the initial breakdown of the log, the planks are re-sawn on a bench circular saw to remove the edges (wain - the original under-bark surface with or without bark on the edge of a piece of timber) and to obtain the desired board width. Variations on this basic sawmilling process are used in all traditional mills around the world. The Vietnamese process, which by western standards, is very labour intensive but has very low capital outlays. A complete sawmilling operation in Australia or the USA would cost over 5 million dollars, with a processing capacity of 50,000m3 pa but would only employ a few people. In comparison the Vietnamese style of sawmilling is very cost efficient when taking into account the size of the country and the distances between the timber resources. Survey The survey undertaken as part of this project provides a snap-shop of a rural industry that has expanded very rapidly in the last decade following the maturing of acacia and eucalypt plantations. There are similarities in the responses to the survey conducted in North, Central and South Vietnam. The expansion has arisen as a result of government policy that has encouraged entrepreneurship and market freedom, a cheap labour force, cheap raw materials 2 (logs), cheap robust saw-milling equipment that has coped with the relatively small diameter logs and a Vietnamese work ethic that has succeeded in building an important rural industry that has flow on benefits to the local community. The first question that arises is whether the “old fashioned” saw-milling equipment has served its purpose and whether more sophisticated saw-milling equipment should be encouraged. In the short and medium term the answer to this is probably no. Sawmill efficiency (conversion of logs into sawn timber) is amazingly high given the quality of logs that are available to most of the rural sawmills. It is unlikely that an improvement in yield could be achieved by introducing more sophisticated equipment. Secondly a very high proportion of sawmills are not operating to full capacity. Equipment breakdown was not identified as a core reason for equipment working below capacity; rather raw materials supplies and inconsistent markets were identified as primary reasons. Higher cost more sophisticated sawmills would exacerbate this problem. The capital cost for establishing a horizontal Vietnamese sawmill is very low, US$3-4,000. The fact that the sawmill is not operating to capacity is unimportant in terms of paying off capital, whereas the introduction of more sophisticated in-feed and out-feed systems and automation would see more than a hundred fold increase in the capital investment needed. This changes the nature of the business from being low cost, rural, part time, seasonal and flexible to being full time, ideally 3-shift, inflexible labour reducing industrial production. Transportation costs for logs to larger fewer mills would increase. Many of the locations currently used by small horizontal sawmills would be totally unsuitable for expansion into larger mills since many are on sites that can’t expand or are located adjacent to dwellings. Visits to a number of integrated forest industry complexes in Central and South Vietnam, that were established in the last 2-3 years to produce very high quality furniture, solely for export identified some very interesting features. Firstly, there was a very high level of occupational health and safety applied to workers. Secondly, very high quality logs of beach and oak from Germany; oak from Russia; cherry and pine from the US, teak from the Philippines and hardwoods from South America etc. were being imported as raw materials for furniture manufacture. Thirdly, some of the most sophisticated computer controlled furniture manufacturing equipment (in one enterprise valued at $US80million) had been imported for manufacturing knockdown furniture components for export. Saw milling however, employed a bank of Vietnamese horizontal sawmills (in one case, 20 horizontal bandsaws in a row) to provide primary conversion of very high value logs into high value sawn timber for subsequent processing into high-value quality furniture. Very clearly it would be relatively easy to write a case for employing a US$2-5 million sawmill complex to undertake this function. Such a decision had not been made primarily because the cost of 21 horizontal bandsaws is still a fraction of the cost of a fully integrated sawmill and the conversion rate achieved using the horizontal mill coupled with low labour costs couldn’t justify such an investment. On balance at this point in time there is no justification for trying to encourage a departure from the rudimentary home-grown saw milling equipment currently being used. Improvements can be made to the Vietnamese bandsaw type mills and these will be highlighted in a separate report. Fourthly, value added kiln drying and wood treatment facilities had been established, as well as very well maintained air-drying practices. This is reported separately. Potentially there is no value to be achieved from the government providing financial incentives for establishing more low cost sawmills. The investment needed to establish new mills is low and is best left to market forces. However, at the same time as the survey was 3 conducted audits were undertaken of kiln drying operations. Many of the kilns inspected were imported and of high quality. In addition Vietnamese manufactured kilns ranged from were well-designed units that met the requirements for drying acacia and eucalypt species, through to poor quality in-house built units, which produced questionable quality material. However, operation of these kilns was sub-optimal due to the failure to use fairly basic drying principles and utilisation of standard monitoring equipment (i.e. wet bulbs sensors) to ensure correct operation. In other words drying was achieved using an oven or ‘hot box’ rather than a properly controlled dry kiln. The inevitable consequences of this resulted in drying degrade, non uniform moisture content and / or over drying. This is a training issue since most of the kilns audited had the equipment available for monitoring relative humidity via wet bulb sensors which inexplicably at times had been disconnected. Most drying operation failed to use baffles. This inevitably led to inefficient energy use and variable wood moisture content both within and between boards, on completion of drying. In addition their appeared to be a lack of adherence to species-specific drying schedules. Whether the best kilns are being used for Vietnamese conditions is also an issue (a research and technology transfer issue). Whilst many sawmills interviewed in the survey identified kiln drying as a business opportunity, clearly there is not enough sawing capacity for each individual mill to justify establishing its own drying facilities. Air-drying requires a great deal of skill and a surprisingly low percentage of sawmills engage in air-drying. Space is an issue for many mills as is training in air-drying practices. There is also a question of the minimum moisture content that could be achieved using air-drying. It is anticipated that this would be approximately around or just below fibre saturation point (fsp). Sap stain, decay and insect attack are important issues in Vietnam primarily because of climate. As soon as a tree is felled it becomes susceptible to this rapid process of colonisation. The lesson is that trees should be left standing until the supply processing chain has been organised and timetabled. Both the survey and quality auditing of the stored logs and finished products indicate an industry–wide problem. Sap-stain is common in logs. Pines and rubber-wood are particularly vulnerable to sap-stain, much more so than acacias and eucalypts. But it is still a problem with these species. Apart from the delays in log transport, other issues identified include proper housekeeping of logs at the mill site; the need in some severe cases for prophylactic treatments at the sawmill to alleviate stain and decay. A high volume of acacias is used in furniture and the survey indicates that this market will continue to grow and substitute the use of acacias in low value uses such as packaging, crates, boxes etc. Much of the domestic furniture uses a dark lacquer finishes. This is an effective strategy in masking stain in wood. However, as the market expands, fashion may change to bring about a demand for furniture that displays the intrinsic species characteristics. This is the case for short clear lengths of rubber wood for export. The market requires a light colour. Export rubber-wood is inevitably preservative treated to prevent sap stain. Ten years ago this would have involved treatment with relatively high concentrations of PCP (Pentachlorophenol – (5%) mixed with borax- (1.5%)). Fortunately given the dioxin impurities in PCP this practice appears to be history and treatment now focuses on the use of boric acid plus borax that is benign from an environmental and human toxicity perspective, although the preservative is still quite toxic to fish. Given the trend towards using acacia for furniture, preservative treatment is potentially not an issue for most sawmills. Occupational Health and Safety is a key issue for rural sawmills. Fortunately the survey identified less of a problem in terms of accidents than was anticipated given some of the work practices and the total absence of any work-place control for the prevention of accidents. These issues have been evaluated, reported and recommendations made to improve the working environment. Survey results as to sawmill owner preferences in relation to training, 4 placed a low priority on OH&S. Whilst this could possibly be justified based on survey results, issues such as noise and dust were not considered by the survey of owners but were audited at the time of the survey. Long-term health issues (nose, lung capacity hearing and eye-sight) are of concern. Implementation of current Vietnamese legislation in relation to OH&S needs to be taken on board by mill owners. OH&S training is obviously one of the key strategies in implementing change in the work place. The survey provides some quantification of the basic needs of rural saw milling in Vietnam. The exercise provides invaluable information from which strategies can be developed for improving the performance of the industry. Key issues identified by the survey that require further investigation include the lack of information in relation to log supply. This is an issue that needs to be addressed by the Vietnamese Forest Service. Secondly the inconsistent market demand reported by many sawmills needs to be addressed. This needs an industry wide or cluster approach to providing collective information and quality standards and finally, mechanisms to promote the development of value adding industries such as kiln drying and furniture manufacturing. Training The project undertook training courses for the rural sawmillers coving a range of areas indentified as important to there industry. The topic covered over the two days were as follows; • Wood Science o Tree growth o Differences in hardwood and softwood o Radial, Tangential longitudinal o Density o Water in Wood o Stability and shrinkage • Timber specifications o VFDS o Grading o Timber stability o Performance requirements • Sawing o Equipment o Methods o Back and Quarter o Sawing map • Saw blades o Types o Design o Sharpening • Drying o Process 5 o Air o Kiln o Other • Preservation o Types o Standards o Anti sapstain o Double diffusion o Other • Safety o Environmental o Worker o Fire • Maintenance • Furniture requirements & design The evaluation reports showed that the training was well received and meet the needs of the participants. Further training courses can be help on individual topic by FSIV staff as and when required. Drying The project found that there was a general lack of understanding of the basic principles of drying lumber by the workers and kiln operators. Kiln operators often used the rear of the kiln as a place of residence. Kiln condition appeared to be controlled on a set and forget basis. In particular there appeared to be a lack of understanding, by the operators, as regards the relationship between dry bulb (DB) and wet bulb (WB) temperatures, airflow and timber racking and the overall effect that these parameters have on the conditions inside the kiln and the resultant non-uniformity of drying of the lumber if they are not correctly monitored and controlled. More specifically it was often found that WB sensors were disconnected (possibly by the operators) from the kilns control system. This meant that the kilns were solely controlled on DB temperature alone, in effect creating a ‘hot box’, with no humidity control. The operators appeared to have made this decision to control the kilns only by DB temperature, purely to simplify the process through lack of understanding of the actual relationship between DB and WB temperatures. It was reported at one facility that as they had dried using the same schedule (i.e. using DB and WB temperatures) that the operator knew from past experience when to change condition based on the DB temperature alone. Where sensors were correctly installed they were only used for manual control, that is, the control of kiln conditions relied basically on the operator monitoring the temperature (i.e. WB and/or DB) and making a ‘uneducated’ decision to open or close the appropriate valve or vent, which was set and forgot until next time he happened to check the reading. 6 Humidity control was generally based on a random basis depending on the gut feeling of the operator. It was reported at one facility that the humidity control consisted of “turning the stop valve, mounted on the external wall, ‘ON’ until water ran out from under the door”. Only one kiln drying facility visited had fully automated controls ensuring 24 hour control of the drying conditions inside the kiln. The use of baffling to restrict by-passing around stacks was nonexistent. Also it was observed on one occasion that boards were rotated 90° to the airflow in order to stack more material inside the kiln in order to fill up the remaining space inside the kiln which did not allow for a full length board. This had the effect of blocking any cross flow between the boards due to the placement of stickers at regular intervals. Further it was observed that kilns were generally stacked to ‘maximum capacity’ with little regard to leaving sufficient ‘plenum’ space between the edge of the stack and the side of the kiln wall. This has the effect of creating uneven airflow through the stack, from top to bottom. On some occasions the plenum space was filled up with surplus material that required redrying. This practise only leads to reduced efficiency of the kiln. With respect to timber stacking it was found that there was a lack of use of dedicated material for ‘stickers’. In general boards were racked out using the same material that was being dried, by placing the components or boards at right angles in a ‘crosshatched’ fashion to create the gap between boards in order to allow airflow. This meant that often the gap was too wide, consequentially reducing the efficiency of the kiln. Preservation The industrial preservation industry in Vietnam is relatively small and is not serviced by any extensive research or training capacity. Because of the climatic conditions in Vietnam, the bio-deterioration of wood products is rapid and needs policy initiatives at the National level to ensure that protocols are established to enhance the durability of wood products. The rationale for this is several fold. • There is a substantial investment in infrastructure at the national level that needs to be protected. • The degradation of wood products leads to the release of sequestered carbon. Expanding the economic life of wood based products has a major impact on carbon storage that is valuable in international efforts to roll back climate change. • Extending the useful life of wood based products in rural communities (where currently most timber is used) has a major impact on the quality of life for rural people by providing more time otherwise spent on replacing or repairing degraded wood products. Examples of this include the use of bamboo for building piles. Left untreated the bamboo piles are continually being replaced, whereas if treated, the bamboo may last for an excess of 15 years before requiring maintenance. Recommendations for preservation are as follows: Research: The key to developing a national approach to preserving wood is having an effective research team focused on all aspects of wood preservation. The research team (perhaps a Centre of 7 Excellence established between the Forest Research Group in Hanoi and the 2 major forestry universities located in Hanoi and Ho Chi Mihn City) should have a focus not just on research but investigating and implementing systems to ensure that a wood preservation sector is established that effectively enhances the performance and service life of wood products. The research team will need to comprise 2 mycologists (one focused on sap-stain, mould control and service life assessment) and the other on laboratory decay assessment of natural durability and new preservative formulations), an entomologist, surface coatings chemist, analytical chemist and wood treatment expert (wood scientist) and qualified technicians to assist the work program. The leader of the group needs to understand commercial research and be familiar with the workings of governments and departments charged with responsibility for managing national standards. The team needs also to have strong linkages to a wood drying research group and research groups focused on wood anatomy, life-cycle analysis, forestry, economics and statistical analysis. The research program needs to focus on the following issues: • National standards of wood preservation • Markets for preservative treated wood • Pressure treatment technologies • The treatment of refractory wood species • “Uni-treatment”, diffusion treatment and double diffusion treatments. • Wood conditioning (including microwave conditioning of wood) and wood drying • Protection of wood from sap-stain and the preparation and interpretation of mill trials to determine optimum applications of anti-sap-stain chemicals. • Assessing the life cycle of wood preservatives and their fate in the environment • The use of chemical modification of wood surfaces • Surface coatings to enhance serviceability • Disposal and recycling of toxic preservatives • OH&S issues associated with the application of wood preservatives • Laboratory decay assessment of new wood preservatives. • Performance requirements for wood products and commodities. Training and education in wood protection Training and education issues are reported separately. However, in essence, wood preservation (wood protection) can be taught by the research group identified above in each of the key areas as follows: • Wood treatment including sap-stain control • Causes of wood deterioration • Mechanism of action of wood preservatives • Preservative compounds • Preservative treatment methods • Natural durability • Boron /fluoride treatments (diffusion) • Light organic solvent treatment 8 • Heartwood treatment requirements • Quality control. • Dimensional stability • Fire retardant treatments • Environmental management • Remedial treatment While different levels of training in wood protection can be identified, in essence the bulk of information needed by practitioners, government departments, local authorities, industry, education teachers for rural communities etc, falls within the levels of 4-6 in complexity within a range of 1-8, (Level 1 Basic competency in handling treated timber: Level 8. PhD). Levels 1-3 are best supervised by industry within the work place, or in the case rural training by extension officers attached to the forestry department while levels 7 and 8 and best supervised with a graduate and post graduate perspective by the universities. It is anticipated that the training components identified above would need one week of block delivery. Total numbers of students per year needing training at the level 4-6 above would probably stabilized to about 20-30/year. However, specialized 1 day workshops can also be organized to assist with specialized issues such as sap-stain control where numbers ranging from 50 - 100 individuals might be anticipated. The key to providing level 4-6 training to groups of students with variable educational backgrounds is to provide first class lecturing materials designed for self learning that can be made available on the internet before the course starts. The materials needed would be provided by the research team identified above or could be obtained from the author of this report. Wood preservation standards A fairly radical approach to wood preservation standards in Vietnam is recommended. The approach starts with the adoption of “Hazard classes”. These were first introduced by New Zealand and Australia in the early 1980’s and then adopted in many other parts of the world over the last 30 years. In the current instance, in Vietnam, it is recommended that the hazard class concept is reduced from the 6 classes used in Australia and New Zealand to two classes: (i) Timber in ground contact and (ii) Timber out of ground contact. The ideal situation given the high decay hazards in Vietnam is to provide virtually all wood with some form of protection. However, the strategy adopted needs to bear in mind the intrinsic natural durability of the timber species selected within a particular end-use and the life cycle consequences of some of the more toxic preservatives. These issues are discussed separately. Wood treatments A radical approach is also recommended in relation to preservative treatment methods adopted in Vietnam. OH&E issues are demanding more stringent methods of applying preservatives. In many tropical countries the wood species available tend to be difficult to impregnate with conventional pressure impregnation technologies. The sapwood of all wood species is perishable and needs preservative treatment. Where the heartwood of a wood 9 species has some durability, preservative treatment of the heartwood is usually unnecessary. Identification of the species is therefore a prerequisite. The heartwood of acacias has some durability and therefore preservative treatment for major uses such as furniture, joinery, flooring and packaging, (the major end uses for acacias) is mostly unnecessary. However, Acacia logs are small in diameter and while the sapwood band is relatively narrow, preservative treatment of the sapwood is desirable. Further research is required to ascertain the relative permeability of sapwood and it is recommended that research is undertaken using the unitreat process where some pressure differential can be achieved to achieve better sapwood treatment than heartwood treatment. Unfortunately no such work has been undertaken to ascertain the treatability acacia sapwood and is therefore a high priority research area. If the sapwood is refractory for example because of tyloses (blockages in the longitudinal vessel elements of the timber), then potentially diffusion treatment will be required to achieve any preservative penetration. Such treatments are successful with green (freshly sawn) timber only and is best conducted on machined timber to avoid the generation of preservative treated wood waste arising from machining. Preservative application for diffusion treatment is traditionally applied by momentary immersion. Momentary immersion often leads to dripping and as much as 50% of the preservative applied by momentary immersion can be lost by dripping. Double diffusion treatments are recommended for timbers destined for ground contact whether round-wood or sawn. The methodology employed during double diffusion is appended to this report. Once again, world-wide, very little research has been undertaken on these treatment methods. And substantial research is required to optimize treatment parameters None-the-less the methodology is ideal for rural use and or industrial production. One other methodology that has potential for rural areas comprises the use of bandages. This is ideal for rural use for example power poles, fences, pole foundations. The methodology is appended (appendix 1) and new systems have been developed recently in Germany. Once again the methodology has to be adjusted for Vietnamese conditions. This requires local scientists to undertake the research and achieve technology transfer into rural areas. Preservatives Wood protection research in Vietnam should focus on the use of non-toxic preservative compounds. Fortunately PCP is no longer used in Vietnam and there are a range of preservatives available that are less toxic to humans and the environment. Whilst the main hazard for timber used above ground comprises insect attack, it is recommended that a fungicide is incorporated into preservatives used for above ground hazards. Boric acid / borax are readily available in Vietnam. Boron is an ideal preservative in that it has low mammalian toxicity (note that it is still toxic to fish) and provides both insecticidal protection and protection from fungal attack. In fact boron is very successful as a fungicide in killing decay fungi once it becomes established in the wood. It should be noted that boron based preservative are not good mouldicides or sap-stain fungicides but often provide some synergy when applied in combination with other fungicides. Examples include the use of benzalkonium chloride (AAC) which is quite effective as an anti-sap-stain fungicide when used in conjunction with boron. As an anti-sap-stain chemical the preservative combination is relatively non-toxic and is cheaper than many proprietary formulations. Research capability is required in this area to undertake mill trials because fungicidal tolerance can build-up. This necessitates continuous monitoring and preservative replacement when tolerance builds up. 10 Contact insecticides can be added to boron or fluoride to enhance their activity against insects. Insecticides based on pyrethroids or fipronil are suitable but clearly need to be emulsified to render them compatible with water-based preservatives. Such formulation chemistry is another area of research. It should also be remembered that very little penetration of such organic based, emulsified preservatives is possible through diffusion processes. Contact insecticides can breakdown with time particularly if there is soil contact. Fipronil has advantages in needing very low levels of active ingredient to be effective. The breakdown products of Fripronil are also reputed to have residual insecticidal properties. The preservatives suitable for double diffusion treatment are limited. Copper sulphate and sodium fluoride are recommended in this report because of their relatively low toxicity. However, the efficacy of such a preservative is relatively unknown and requires further research. World-wide there is now interest in the chemical modification of wood and also in surface activation of the timber so that surface coatings achieves a longer life, particularly in exterior applications. Details of surface activation technology are available from the internet for example from the Cooperative Research Centre Wood Innovations web-site, Australia. Relatively little research is available relating to surface stabilization of wood through chemical modification. The theory is that chemical modification achieves bulking of the cell wall and cross-linking of wood components such as cellulose such that swelling and wood shrinkage are reduced considerably. The process of shrinkage and swelling usually puts pressure on a coating system such that the coating becomes ruptured resulting in the ingress of water. What is less well understood is the depth of chemical modification required to achieve surface stabilization. Once again, this is an important area of research that needs to be conducted to suit local conditions. Treated wood waste disposal There is public concern relating to the disposal of treated wood waste. In the past such waste has been disposed into landfill. This is now becoming expensive and unacceptable to the general public as well as public health and environmental managers. In developing wood treatment strategies, considerable thought needs to be given as to how waste preservative might be recycled or managed into low hazard applications. This requires a national strategy because of the logistics and costs involved. It is beyond the scope of this report to provide a detailed recommendation other than to drawn attention to the issue and highlight a treatise on the subject. Recommendations The following is a summary of the recommendations from this project; Policy Recommendations • The centralization of the sawmilling industry to a few strategic locations would not be an economically prudent option. The existing system relies on a large number of self fund operations who are versatile enough to meet changing market needs. • The development of kiln drying facilities in central locations to handle the drying for a number of sawmills would be advantages to add further value to the sawn products. [...]... quality and size should be reflected in an increase price paid by the sawmillers for these logs • There is a need to guarantee the supply of logs to the sawmillers Training recommendations • Training in kiln drying is required to bring the industry up at a standard that will allow them to compete in the international market and produce a constantly uniform product • Training of sawmillers to understand...• A review of the safety standards for saw milling should be undertaken especially with respect to noise and the long term damage constant noise can have on hearing • For the sawmilling industry to be competitive, internationally, the log diameter need to be larger and log quality improved Growers should be encouraged to undertake management practices that will improve log quality and diameter This... allow them to compete in the international market and produce a constantly uniform product • Training of sawmillers to understand the structure and nature of wood and how they can process it better • Training into the international requirements for timber products and the consistency in quality for furniture components is essential for those sawmillers wishing to venture into furniture manufacturing • . Improving operator skills and technology for small rural sawmills Processing, preservation and using wood of plantation forests Philip Blackwell: University of Melbourne, AVI and FSIV Pham Duc. microwave conditioning of wood) and wood drying • Protection of wood from sap-stain and the preparation and interpretation of mill trials to determine optimum applications of anti-sap-stain chemicals technologies. The sapwood of all wood species is perishable and needs preservative treatment. Where the heartwood of a wood 9 species has some durability, preservative treatment of the heartwood is usually