The bases of special methods of biomass processing into prospective materials


The Ministry of Science and Higher Education of the Russian Federation Kazan National Research Technological University








A. R. Shaikhutdinova, R. R. Safin



        THE BASES OF SPECIAL METHODS OF BIOMASS PROCESSING INTO PROSPECTIVE MATERIALS

    Tutorial



                        Учебное пособие содержит сведения, необходимые для формирования профессиональных компетенций при подготовке магистров по направлению 35.04.02 «Технология лесозаготовительных и деревоперерабатывающих производств», и рекомендуется Научно-методическим советом по лесному хозяйству для использования в учебном процессе.





Kazan
                      KNRTU Press
2018

        UDC 674.8.02(075)
        LBC 37.1я7



Published by the decision of the Editorial Review Board of the Kazan National Research Technological University

Reviewers:
Director of PLC Scientific and Production Enterprise «TermoDrevProm», Ph.D. P. A. Kainov, Deputy Chief editor of the Woodworking Industry Magazine, Ph.D. E. Y. Razumov





        Shaikhutdinova A. R.
        The bases of special methods of biomass processing into prospective materials : tutorial / A. R. Shaikhutdinova, R. R. Safin; The Ministry of Science and Higher Education of the Russian Federation, Kazan National Research Technological University. - Kazan : KNRTU Press, 2018. - 100 p.

        ISBN 978-5-7882-2480-0

       The technological processes of treatment of biomass into prospective materials are considered in the textbook.
       Intended for Master’s Degree Students of the Faculty of Power Engineering and Technological Equipment of the direction of training 35.04.02 «Technology of logging and wood processing industries» under the training program «Energy-saving technologies for processing forest resources into promising materials» (the discipline is «Basics of special methods of biomass processing into prospective materials»), as well as for post-graduate students and teachers.
        Prepared at the Department of Architecture and Design of Wood Products.



                                                 UDC 674.8.02(075)
                                                 LBC 37.1я7

ISBN 978-5-7882-2480-0     © Shaikhutdinova А. R., Safin R. R., 2018
© Kazan National Research Technological
University, 2018

INTRODUCTION


       The question of exact definition of the term «biomass processing» still remains open. For someone this is the separate manufacturing enterprise where biomass - wood, sugar beet or corn is processed into different types of bioproducts, for example the products like chemicals or materials, received in small amounts, or less valuable modern types of biofuel, made in considerable volumes.
       The modern world needs new, ecologically safe technologies. It requires the solutions which can be provided due to biomass processing.
       The enterprises for biomass processing working at different types of renewable raw materials are already designed worldwide, though there is an opinion that the real full processing of biomass just should be organized. In countries of Northern Europe the experimental productions on processing of biomass release modern types of biofuel, using by-products of the enterprises of pulp and paper industry as raw materials.
       In many countries energy security, environmental issues and the development of alternative clean sources of raw materials for the manufacturing and chemical industries will in the near future be a challenging commitment to make important decisions. There are already incentives for the development of the energy and chemical industries based on renewable resources. The development of the production of what we define by the term “first generation biofuels” can be viewed as a necessary step in the development of technologies leading to a resource use system that is non-depleting and appropriately maintained in a benign environment.
       The magnitude of damage caused to nature by human activities, commensurate with the production and use of energy from fossil fuels, as well as some chemical products and materials, has led us to the need to develop new production systems based on the principles of reducing environmental pollution, the rate of hazardous materials and creating production of environmentally friendly products. This requires the organization of continuous supply of renewable raw materials with low emissions of carbon dioxide.
       Globally, the only source of such raw materials is biomass, which contains the same elements that are part of fossil energy sources in various combinations.

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1. GENERAL DATA ON SPECIAL METHODS OF BIOMASS PROCESSING


1.1. The concept of biomass

       The source of wood is trees, perennial plants having a well-marked trunk, rootage and branches forming the crown.
      According to the existing technology a trunk while lumbering is separated from a stump and a tip. As a result the trees are divided into:
      -  trunk................60-65 %;
      -  stump and roots..........15-30 %;
      -  branches and tip.....15-20 %.
      Trunks being primary raw wood are processed into lumber (round wood, precut wood, shelled wood, dressed timber, timber brought and disintegrating wood) for various purposes. The harvested wood is divided into industrial wood used in manufacturing and firewood used as fuel.
      While harvesting and processing there are different kinds of wood waste that can be considered as secondary wood-products.
      Secondary wood-products are waste-wood that appear due to logging, mechanical processing, chemical-mechanical processing, chemical processing of wood, usage of wood work and tree trimming waste. All these secondary wood-products can be used for technological, fuel and energy and other purposes.
      This can be either wood itself, e.g. lump waste or soft waste (shavings, sawdust, wood dust) of wood processing or by-products of its chemical processing (organic part of boiled-off liquor, sewage sludge, fiber waste, hydrolytic lignin, etc).
      One should mention the composite in homogeneity of wood. This happens due to homogeneity of wood biomass.
      The tree biomass is the total mass of all its parts. The tree biomass consists of three components - wood, bark and wood foliage. In this particular case wood is parts of a trunk, branches and roots.
      Wood foliage consists of scions and leaves (leafage and needles) that are not lignified. These biomass constituents have different functions in a growing tree. That is why they differ according to their structure and composition. Qualified processing of all biomass components requires their preliminary division.


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1.2. Classification of wood composite materials (WCM)

       Composite materials are the materials consisting of two or more mutually insoluble components (phases), having a visible boundary between them and an adhesive contact. One of the phases is called matrix and another is reinforcing element or filling compound.
       Wood composite materials include matrixes filled with wood of different state. In the following cases the binding agent plays the part of the matrix where mechanical wooden framework is placed. This filling gives wood composite materials special mechanical properties such as high strength and approximately low density. High strength is achieved due to mechanical properties of reinforced wood. It constitutes a strong and firm structure together with matrix materials.
       The classification features of wood composite materials:
       1) type of filling;
       2)  type of matrix;
       3)  basic quality index (average density);
       4)  usage areas.
       According to the first feature “type of filling” WCM can be divided into three groups:
       1)        materials made of solid timber. This group representative is modified wood. Soft broadleaf wood is used for its manufacturing;
       2)        materials made of rotary cut veneer. Impregnated with synthetic resin and compressed at high temperature and pressure veneer sheets form wood-base plastic laminate (WPL);
       3)        materials filled with discrete particles. This group of filling agents consists of woodworking waste products, lumber waste of various shape, size and granulometric composition.
       Types of discrete particles:
       1)        Fiber is used for fiber reinforced gypsum panels (FRGP) manufacturing, fiber board (FB); It is obtained by milling chip in special machines - defibrators. Fiber length is 0.7-2 mm, the average diameter is 0.04 mm.
       2)        Hogged chips is part of cement wood; These are sheet-like or needle-shaped particles with the length of 2-20 mm; These particles are obtained from lump waste (slabs, laths, off cuts, veneer sheets) by processing on chippers and hammer mills.

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      3)        «Wood wool» is used in fibrolite manufacturing. Fibrolite consists of chips with the length of up to 500 mm, width of 2-5 mm and thickness of 0.2-0.7 mm; It is obtained by shaping pieces of log in wood wool machines.
      4)        Bark is used for manufacturing of heat-insulated material, which consists of chopped particles of 10-40mm long.
      5)        Shavings are used for manufacturing of wood particle boards (WPB), cement bonded particle boards (CBPB), goods made of moulded impregnated wood. It is a sheet-like particle 2-20 mm long, 0.2-0.5 mm wide.
      6)        Shaving-waste is used for manufacturing goods made of moulded impregnated wood and some kinds of sawdust concrete. It is obtained while processing wood on planning, milling and other machines. They are no more than 15 mm wide, no more than 2 mm thick.
      7)        Sawdust is used for manufacturing goods made of moulded impregnated wood, gypsum-saw blocks (GSB), sawdust concrete, xylolite and other materials; Sawdust is obtained by sawing wood. These are particles of 0.5-4.5 mm wide and thick.
      8)        Wood chip is used for manufacturing goods made of moulded impregnated wood. These particles are obtained through crushing veneer sheets that are not used in veneer plywood manufacture. The length of the particles is 50-80 mm, the width is 5-10 mm, the thickness is up to 1.8 mm.
      Discrete particles of plant fiber can also be used in wood composite materials. According to their morphological structure and processing techniques discrete particles are divided into two types:
      1)        particles that cannot be ground (ground rice peeling, sunflower, lint boon);
      2)        crushed particles that are obtained by processing raw material in feed mills or rotary choppers (cotton stalks shred, straw shred, etc).
      According to the second feature (matrix type) - all the WCM can be divided into three groups:
      1)        Synthetic polymers are used as a matrix. The result is composite molded impregnated wood, WPB, WPL, FB. Phenol-formaldehyde resin, urea-formaldehyde resin and other synthetic polymers are used as binding agents in materials of this type.
      2)        Nonorganic cohesive materials are used as a matrix. They are straight cement, (cement wood, CBPB, sawdust concrete, fibrolite), gypsum (GSB, fiber reinforced gypsum panels (FRGP)).

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       3)        Natural bonding agents or resins are used as a matrix. Such materials are piezothermoplastics and lignocarbonhydrated plastics.
        The third feature, the basic quality index, is average density that divides all the WCM into 2 groups:
       1)        Light materials with the average density of less than 1200 kg/m³. These are modified wood, FRGP, fibrolite, cement wood, karbolite, gypsum-saw blocks (GSB).
       2)        Heavy materials with the average density of more than 1200 kg/m³. These are construction blocks, CBPB, goods made of moulded impregnated wood, piezothermoplastics and lignocarbonhydrated plastics.
       The fourth feature is sphere of usage. It differentiates the sphere of WCM usage into different sectors of national economy:
       1)        materials based on mineral binding agents are used in construction (They are cement wood, CBPB, fibrolite, xylolite, FRGP);
       2)        modified wood is used in construction, transport, mineral resource industry and light industry;
       3)        wood-base plastic laminate (WPL) is used in mechanical engineering, chemical industry and radio industry;
       4)        goods made of molded impregnated wood are used in furniture production, packaging and automotive industry.

1.3.  Wood composite material (WCM) molding process classification

       In spite of the fact that there are many types of WCM the technological process of their production consists of the following operations:
       -  pre-operations with raw materials;
       -  combination of matrix and filling;
       -  mixture measuring;
       -  compressing;
       -  thermal treatment;
       -  finishing of the obtained material.
       The most important operation influencing the physical-mechanical characteristics of the obtained material is molding. Molding is a process when a composite material gets a required form. Compressing and thermal treatment of specially prepared wood combined with matrix material constitute the basic part of the process. Consequently, plates of different types, trim moldings and piece works are obtained.


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       Wood composite material (WCM) molding process classification Wood composite materials can be classified according to:
      -  the direction of compacting force applied to a product;
      -  the degree of working area limitation where molding takes place;
      -  the type of molding method;
      -  the organization of molding processes.
       According to the first feature, direction of compacting force, one can define:
       1)        Flat molding occurs when compacting force is directed perpendicularly to a face. Wood particles are parallel to the product surface. Such products have the same or different density along and across face. That depends on particle orientation. This method is used in the United States to manufacture solid wood door leaves 35-40 mm thick with density of 640-1140 kg/m³ from sawdust. Molded lining door panels 3.6 mm thick are manufactured in Sweden and Germany. They imitate paneling and are used in doors of folded plate structure with honeycomb corestock. Technology of their production is similar to production of WPB. Panels are covered with paper film, impregnated with phenol-formaldehyde resin. Moreover, flat molding is used for manufacturing wall panels, floor moldings, plat bands, picture frames, and fronts for kitchen furniture of different shape, parts for beds, chairs, tables, interior trim and containers. Flat profiled panels such as CBPB, FRGP and cement wood are obtained in the process of flat molding.
       2)        Extrusion occurs when compacting force is directed parallel to a product face. Wood particles are perpendicular to product’s surface. Mechanical article strength of such products is lower in both directions than that of flat molding. In case of extrusion trim moldings from wood-adhesive composition and construction blocks can be obtained.
       To get complex parts from low flow compositions combined molding is used. In this case deformation effort of wood composition in a molding process changes its direction. This molding takes place in the manufacture of single-molded boxes using several plungers that operate simultaneously or sequentially.
       There is direct and injection molding. In direct molding the woodpolymeric material is put into an open press-mold. Press-mold closing and filling take place under plunger pressure. With vertical effort the press covers side walls of press-mold providing equal distribution of pressmaterial.

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       A method of transfer molding (injection) can be applied to complicated products made of the masses of wood-pressing of high penetration. According to this method previously softened in the transfer cylinder material is squeezed with the help of a plunger into closed cavity of a press-mold through running channels.
       According to the second feature, degree of working area limitation, there can be the following types of molding:
      -  between mold plates;
      -  in calenders;
      -  in a channel by extrusion;
      -  in press-molds.
       Sheet material is obtained between mold plates and in calenders. Sheet profile matches the reverse profile of mold plates or surface of calender.
       Wood-polymer compound molding in heated channels allows us to obtain sheet material or trim moldings depending on channel profile.
       Press-molds can be open or closed. They are used to manufacture piece works or goods from wood-adhesive composition (WAC) and woodpolymeric materials (WPM).
       According to the third feature - the nature of the molding process, there can be the following types of molding:
      -  batch;
      -  continuous;
      -  pulsating method.
       Periodic molding process occurs in batch press-molds. As a result flat profile panels (in molding between mold plates) or goods of different form (in press-molds) are obtained.
       Continuous molding process is implemented in calender pressmolding machines where panel or sheet material can be obtained. It is also carried out in a fixed channel using an operating element made as a steel strip or а screw. This method has a number of advantages in comparison with batch molding method. It allows obtaining goods of different length in one press without decreasing press usage ratio. It leads to process automation, etc.
       Pulsating molding process is characterized by the fact that a force causing molding material deformation is not constant, but periodically changing within limits. Profile, panel or other kinds of trim molding (e.g. constructing wood-mineral blocks) can be obtained when using pulsating

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molding method with extruders. Items are obtained when wood-polymeric composition is molded in a matrix channel between half-molds.
       According to the forth feature, molding process structure there can be:
      -  single-position process;
      -  double-position process;
      -  multi-point process.
       In case of single-position process panel material is manufactured in a space between mold plates, and items are produced in press-molds. Different methods of press-molds in a press are possible. Press-molds can be voluminous and stationary (built-in press plates). The distinctive feature of this method is that technological molding process operations like compaction, heating, conditioning, cooling, unloading of finished items, etc. are concentrated in one place - a press. Due to a long duration of these operations press efficiency is very low.
       In case of double-position molding process wood-polymeric composition is pressed in a cold press. Then it is placed into a hot press for finishing molding. This process is more efficient than cold one as multiopening presses are suitable for hot-pressing. However, double-position molding method requires a lot of press-molds, transport facilities and additional working areas.
       Wood-polymeric composition pressing and mold closure are performed in a multi-point press. Other operations like heating, technological conditioning, cooling, press-mold opening are realized outside press on a conveyor. To ensure undisturbed operation of a conveyor a great number of press-molds is required.
       The disadvantages of multi-point process apart from great number of press-molds are the size and bulking of nonstandard equipment like conveyors, pneumatic actuators, push-type-actuators, pot heaters, and cooling ovens.
       Besides, all these additional working areas are required. Due to the previously mentioned factors multipoint press method has no industrial application in wood-polymeric material production. But method is used in industrial production of wood-mineral composite materials (cement wood and CSP).

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