Broadband Wireless Access and the 5 th Generation of Mobile Communications

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2 Broadband Wireless Access and the 5 th Generation of Mobile Communications George T. Karetsos Department of Computer Engineering Technology Education Institute of Thessaly Larissa, Greece karetsos@teilar.gr Fotis Foukalas Department of Electrical Engineering Qatar University Doha, Qatar foukalas@qu.edu.qa Abstract Despite the fact that 4G deployment is still at its infancy there are already many research initiatives that focus on the next generation of mobile communications. But why there is a need for a new generation to be shaped so closely to the previous one? Is it really a need behind it by the community or the companies are seeking new ways to sustain or enhance their profits. In this paper we highlight the forces that push towards the 5 th generation of mobile communications and we discuss the technologies that are envisaged to make it a reality. Keywords Broadband Wireless Access; MU-MIMO; cognitive radio; coordination multi-point transmission; small cells This prediction is supported by the fact that the mobile cellular subscriptions are approaching the global population figures [3]. In addition the mobile-cellular penetration stands at 128% in developed countries and 89% in developing ones leading to a mean of 96%. Thus it is obvious that we are approaching a market saturation. However one of the most interesting findings reported is the fact that the mobile broadband subscriptions have grown from 268 million in 2007 to 2.1 billion in I. INTRODUCTION In a recent press release the European Commission Vice President Neelie Kroes announced a 50 million grant for research to deliver 5G mobile technology by the year 2020 [1]. The ultimate goal of this initiative as communicated by the officials is to put Europe back in the lead of the global mobile industry. Of course this is good news for researchers and for companies but what about the people? Is there really a need for such an investment? In order to answer these questions let s have a look into where we are right now and what the numbers are telling us. With the explosion of smartphone usage the biggest percentage of traffic exchanges is data and not voice. Data transfers are served for the moment by 3G networks which however see their capacity to reach its limits. This is why many times voice traffic is being directed and served by the coexisting 2G networks. To get an idea on how the mobile data is going to grow a recent report by CISCO states that a 13-fold increase is expected by the year 2017 corresponding to a 66% compound annual growth rate [2]. Fig. 1. Predicted annual mobile data growth [2] Fig. 2. World population and mobile cellular subscriptions converge [3] In the path towards 2020 another major mobile data traffic generation source will be machine to machine (M2M) communications or Internet of Things (IoT). M2M will play a crucial role in our future everyday life since they will provide us with the ability to monitor and control numerous parameters and devices at real time. For example a heart rate monitoring sensor will gather vital data from our heart and transfer them periodically for storage in a database which is subsequently accessed by a physician. In addition our refrigerator can inform us after communicating with our smartphone regarding what should be included in our shopping list e.g. when a product is missing or it has reached a threshold of inadequate quantity. All these transactions can take place and most probably will be fulfilled wirelessly. On the other hand, despite the fact that 4G is just around the corner, it seems that won t be able to support the forecasted growth of mobile data. Some reports state that the nominal rates of 300 Mbps are not possible in real deployments and only 50Mbps rates are achievable at the downlink. It is obvious from the above that there is really a need for technologies that will support the enormous amounts of data that will be transferred wirelessly in the near future. 1

3 The most important aspect in this direction is the air interface which is supposed to support up to 10 Gbps peak data rates with 8~10 bps/hz/cell. Such transfer speeds may appear non pragmatic but they may not. In May 2013 Samsung has announced a successful test where a rate of 1,056 Gbps was achieved via the 28 GHz frequency band, using 64 antenna elements at a distance of 2km [4]. To make it more practical such a perspective means that real-time streaming of ultra-high definition (UHD) movies over wireless will become a commodity in the near future. The key technologies that have been recognised as those sufficient to enable 5G include the following: Large-Scale Antenna Systems otherwise known as Massive MIMO and mmwave communications, coordination multi-point transmission (COMP) technologies, cognitive and reconfigurable wireless networking for dynamic spectrum allocation, advanced multiple access and modulation schemes, techniques for heterogeneous and cooperative communications, small cell deployments. Furthermore, energy efficiency is considered an equally important aspect that is envisaged to be fully integrated in the 5 th generation of wireless communication systems for environmental protection reasons. The rest of this paper is structured as follows. Section II reports on Large-Scale Antenna Systems and mmwave communications. Section III on coordination multi-point transmission technologies. Section IV reviews cognitive and reconfigurable wireless networking. Section V presents the concepts of small cells and heterogeneous wireless networking and we close in section VI with concluding remarks. II. LARGE-SCALE ANTENNA SYSTEMS AND MMWAVE COMMUNICATIONS Multiple Input Multiple Output (MIMO) antenna technology for wireless communications is now commercialized and has been incorporated into the latest broadband wireless standards like IEEE n and LTE. The increased number of antennas offers increased data rates and link reliability via the exploitation of multiple signal paths among the transmitter and the receiver at the cost of computational power and energy consumption. In Large-Scale Antenna Systems or massive MIMO a large number of low power antennas is being used so that it is possible to focus the radiated power in small areas. Although such deployments have been used only experimentally the number of antenna elements used varies between 32 and 128. For example the ARGOS prototype is using 64 elements while the ARGOSv2 is using 96 [5]. Building a system with such numbers of antennas serving many users in parallel is not an easy task. The most important factor that needs to be taken into account is the fast fading nature of the wireless communications channel. Since we speak about multi user MIMO (MU MIMO) the base station must have accurate channel state information (CSI) for each user in order to be able to calculate the associated precoding vectors [6]. This procedure should be done for all users within the channel s coherence time a task that it is very demanding in terms of speed for the baseband processing subsystem. Massive MIMO is the evolution of MU-MIMO with the employment of much more antennas. The advantages of MU-MIMO can be summarized in the following: a) increased data rates, since more independent data streams can be sent out and more terminals can be served simultaneously. b) enhanced reliability, since more different propagation paths are formed by incorporating multiple antennas. c) improved energy efficiency, because the base station can focus its energy where the terminals are located; and d) reduced interference because the base station can avoid transmitting into directions where it has been identified that the interference temperature will increase. In figure 3 a sample MU-MIMO configuration is presented [7]. This would converse into massive MIMO if the antenna elements are increased. For example 128 in the base station and 16 at the terminal. Fig. 3. Sample MU-MIMO configuration with 8 transmitters and 8 receivers [7] Studies on massive MIMO have been carried out for both isolated and multiple cells [8]. It has been shown that in single cell configurations and under all reasonable propagation conditions, increasing the number of base station antennas permits a reduction in base station power. It is also possible to assign each terminal an orthogonal pilot sequence without the need to overtrain. On the other hand in multiple cell schemes the large number of base station antennas can eventually alleviate all noise, and eliminate both intra-cell and inter-cell interference. However since there aren t enough orthogonal pilot sequences available for every user they should be re-used. Usage of Millimeter wave (mmwave) communications i.e. going up in the spectrum seems inevitable yet promising for future cellular systems. This is due to the fact that limited spectrum is available for commercial cellular systems. With mmwave cellular systems rates in the order of gigabit per seconf can be achieved. However in these frequencies we have to cope with the specific propagation characteristics and associated channel impairments. One of the main problems as far as propagation is concerned is the fact that free-space path loss is much larger. On the other hand scattering is not so prominent as in the legacy cellular systems leading to reduced diversity. In addition, due to the usage of larger bandwidth channels noise power is larger. 2

4 An important aspect in such deployments is to have a uniform signal-to-noise-ratio (SNR) over the complete cell s area. To achieve this outcome mmwave networks can rely on controllable directional antenna arrays with large number of elements. This is not a difficult task since due to the small wavelength employed we can fit many elements with the appropriate distance between each other in relatively small panels and provide enough array gain to overcome path loss and ensure high SNR at the receiver. This finding justifies the fact that massive MIMO and mmwave communications are considered as perfect partners for the provision of very high data rates to mobile users. III. COORDINATION MULTI-POINT TRANSMISSION AND RECEPTION (COMP) As we have seen in the previous section with massive MIMO we can cover a cell s area in a quite detailed fashion by focusing the radiated energy in smaller subareas. However when the terminals are located at the cell s edges they are bound to receive signals from the neighbouring base stations as well while the signals from the host base station will be inevitably attenuated. Thus the quality of communication and the rates achieved at the cell s edges will be lower when compared with those achieved near the base stations. Coordination multi-point transmission and reception (CoMP) is a technique that aims to alleviate such a problem and allow mobile users to enjoy consistent performance and quality whether they are close to the center or to the edges of the cell. To achieve the required very high data rates, MIMO is of course still used in such a solution but the terminals will be able to receive signals from their neighboring sites as well. This is done under strict co-ordination in order to eliminate interference as much as possible. CoMP can be applied at both uplink and downlink. In the downlink the target maybe either interference avoidance or interference avoidance and scheduling when the same information is transmitted from multiple sites. In the uplink CoMP capitalizes on the fact that the signals of the mobile terminal are received from multiple sites a fact that can increase its performance [9]. during the design phase on how the processing and the communication between the involved sites is taking place. Communication among the CoMP modules can occur either intra-site or inter-site. In the intra-site approach the coordination happens within the cell site while in the inter-site one multiple sites are involved in the decision making. In intrasite most of the information exchanges happens within the site and does not load the interconnecting links between different sites. On the opposite the inter-site approach may load the backhaul connections significantly and should be taken into account during planning. IV. COGNITIVE AND RECONFIGURABLE WIRELESS NETWORKING Cognitive radio networks (CRNs) can enhance spectrum utilization of licensed wireless networks, also known as primary networks (PN), when certain conditions apply [10] [11]. The underutilized or unused spectrum resources can be exploited by the so called cognitive or secondary networks (SNs) as long as their operation is not harmful for the PN. CRNs are categorized either as opportunistic spectrum access (OSA) or as spectrum sharing (SS) ones [12] [13]. OSA CRNs rely on exploiting spectrum bands when they are not being used by the PN and the power level is adequate for transmission. The system model of an OSA CRN is depicted in figure 5. When a secondary user (SU) has data to transmit relies it attempts to exploit spectrum gaps being available in the PN which are recognized by the SN via spectrum sensing of the PUs (primary users ) activity. Fig. 5. System model of Opportunistic Spectrum Access CRN Fig. 4. Coordination multi-point transmission and reception concept The main problem associated with CoMP is that all the required procedures should be done very quickly since it may lead to significant delays that may finally jeopardize the anticipated performance. Thus special emphasis should be put Fig. 6. System model of a Spectrum Sharing CRN 3

5 On the other hand SS CRNs rely on the co-ordinated sharing of a spectrum band among the PN and the SN. Furthermore if an SS CRN employs spectrum sensing, then it is called sensing-based spectrum sharing CRN [14]. Such a deployment is shown in figure 6. It has been shown in various studies that CR technology can substantially improve the capacity of the secondary network and thus the overall system s throughput efficiency. A joint design of adaptive modulation and power control as well as continuous rate and discrete rate adaptive modulation for the particular CRN types is given in [15]. Closed-form expressions for the average spectral efficiency over fading channels and for the corresponding required optimal power allocation that maximizes the average spectral efficiency are derived. Furthermore numerical results highlight the networks performance and the possible gain of implementing adaptive modulation in CRNs. Going more practical one important application of CR technology is the exploitation of the so called TV White Space (TVWS). TVWS emerge either from the replacement of analog TV with the digital one or in places where despite the fact that there exists coverage from the TV antenna towers there are no receivers. Several regulating bodies are supporting the usage of TVWS by wireless communication systems for the efficient reuse of the unused TV spectrum, which is based on a noninterfering mode of operation. In the standardization front the IEEE Working Group has published the IEEE standard for TVWS broadband wireless access to rural, low population density, areas thus allowing for broadband wireless access where the TV spectrum is least used [16]. IEEE systems offer increased coverage and can provide a reliable solution for broadband access in rural areas. In March 2013 the IEEE Working Group announced that it has completed and published the IEEE recommended practice for installation and deployment of the IEEE standard on Wireless Regional Area Networks (WRANs) and the IEEE standard [17]. Thus it is now about time to start seeing installations of this technology in real deployments. Such activities are taking place through the White Space Alliance which aims to promote the development, deployment and use of standards based products and services as a means of providing broadband capabilities via the White Space spectrum [18] V. SMALL CELLS AND HETEROGENEOUS WIRELESS NETWORKING Small cells are, as the term suggests, low power base stations that operate in the licenced spectrum and aim in filling the coverage holes existing in urban environments covered only by macro cells. Small cells can be femtocells, picocells, metrocells and microcells. Apart from providing improved cellular coverage, small cells can achieve great capacity enhancements since the networking infrastructure is coming closer to the user thus allowing for improved SNR and lower delays. Fig. 7. Small cell coverage limits [19] With small cells we can achieve very good coverage indoors and thus the users can continue to use the cellular network without the need to switch to e.g. Wi-Fi enabled phones. This is very important for the operators since they will continue to serve their clients adequately in buildings as well so that their profits are sustained or even increased. Small cells are considered also one of the core building blocks in heterogeneous wireless networking where different networks need to cooperate. One major requirement that has to be satisfied in heterogeneous wireless networking environments is the support for real time services and applications that are becoming increasingly popular and should be effectively supported end-to-end. Obviously the diverse standards now in operation in the wireless world can be glued together if we rely on small cells. One critical issue with small cells is the fact that their deployment is much more costly than this of macro cells. Thus there is a need to find ways that will enhance the added value of their usage. One proposal that originates from Intel is to add intelligence at the base stations so that they can run network and application services [20]. For example they can be used to run code that improves the compression and transcoding of a video stream. Trials show that such an approach reduced peak traffic loads. This result significantly improved the subscriber s experience as loading web pages and downloading videos is notably faster and reduced the required data rate of the backhaul connections something very important for service providers that lease them. VI. CONCLUSIONS In this paper we reviewed the main architectural aspects and technologies that are supposed to form the 5 th generation of mobile communications. In particular we have reported on Large-Scale Antenna Systems and mmwave communications. Then we described the coordination multi-point transmission and reception technologies. A brief outline of the main aspects related to cognitive and reconfigurable wireless networking was given next. Finally we presented the concepts of small cells and heterogeneous wireless networking. Apart from the possible benefits we outlined also the challenges that need to be addressed before making 5G a reality in our everyday activities. ACKNOWLEDGMENT This research has been co-financed by the European Union (European Social Fund ESF) and Greek national funds through the Operational Program "Education and Lifelong 4

6 Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: ARCHIMEDES III. Investing in knowledge society through the European Social Fund. REFERENCES [1] [2] 05/ns827/white_paper_c html. [3] The World in 2013: ICT Facts and Figures, February 2013, available at [4] [5] [6] Spencer, Q.H.; Peel, C.B.; Swindlehurst, A.L.; Haardt, M., "An introduction to the multi-user MIMO downlink," Communications Magazine, IEEE, vol.42, no.10, pp.60,67, Oct [7] [8] T. L. Marzetta, Noncooperative cellular wireless with unlimited numbers of base station antennas, IEEE Trans. Wireless Commun., vol. 9, no. 11, pp , Nov [9] Juho Lee; Younsun Kim; Hyojin Lee; Boon Loong Ng; Mazzarese, D.; Jianghua Liu; Weimin Xiao; Yongxing Zhou, "Coordinated multipoint transmission and reception in LTE-advanced systems," Communications Magazine, IEEE, vol.50, no.11, pp.44,50, November 2012 [10] S. Haykin, Cognitive Radio: Brain-Empowered Wireless Communications, IEEE Journal on Selected Areas in Communications, vol. 23, no. 2., pp , February [11] L. Khalid, A. Anpalagan, Emerging cognitive radio technology: Principles, challenges and opportunities, Computers and Electrical Engineering, Elsevier Publ., vol. 36, no 2, pp , Mar [12] Q. Zhao, B. Sadler, A survey of dynamic spectrum access, IEEE Signal Processing Magazine, vol. 24, no. 3, pp , May [13] B. Wang, Liu, K.J.R., Advances in Cognitive Radio Networks: A Survey, IEEE Journal Selected Topics in Signal Processing, vol. 5, no. 1, pp. 5-23, February [14] X. Kang, Y.-C. Liang, H. K. Garg, L. Zhang, Sensing-based spectrum sharing in cognitive radio networks, IEEE Transaction on Vehicular Technology, vol. 58, no 8, October [15] Foukalas, F., Karetsos, G.T., On the performance of adaptive modulation in cognitive radio networks, (2013) Computers and Electrical Engineering, 39 (4), pp [16] [17] [18] [19] [20] itepaper_ pdf. 5

7 Morphological characteristics of recovered fibres used in the production of corrugated board in Greece Recovered fibres Stergios Adamopoulos Department of Wood & Furniture Design and Technology TEI of Thessaly Karditsa, Greece Elias Voulgaridis, Costas Passialis Department of Forestry and Natural Environment Aristotle University of Thessaloniki Thessaloniki, Greece Abstract The structure of liners and flutings-medium commonly used by the corrugated packaging industry in Greece were determined on the basis of compositional analysis and morphology of their fibres. Standard fibre analysis techniques and microscopy were employed to identify the fibre components as regards their origin (softwood, hardwood, nonwood) and pulping methods, and to quantify them by using appropriate weight factors. Morphological characteristics of fibres including fibre dimensions, fibre length classes, coarseness, curl, kink, fines content, and fibrillation were assessed by a MorfiTrac device. As a result of the increasing share of recycled raw materials, the papers proved highly variable incorporating a large number of wood and nonwood fibre types. Softwoods and chemical pulp were the most important components in kraftliners, while hardwoods and semi chemical and chemi mechanical pulps were dominant in testliners and flutings. The paper grades were also varied greatly in the morphological characteristics of their fibre components. Kraftliners had the highest fibre dimensions, while kink, curl, fibrillation and fine content were higher in the recycled paper grades within liners and flutings. The quantitative distribution of fibre length classes further revealed the structural differences among the papers as the small fibre class mm had a major contribution in the recycled based testliners and flutings, the fibre class mm had the highest share in semi chemical flutings composed by relative short hardwood fibres, and the large classes mm and mm were found in higher percentages in kraftliners composed by long softwood fibres. Such data, combined with the physical-mechanical paper testing, can be useful in evaluating the performance of paper products which is needed for a sustainable packaging manufacturing. Keywords liners; flutings; fibre composition; fibre morphological characteristics; fibre length classes I. INTRODUCTION The manufacture of corrugated board containers (boxes, trays, etc.) involves a production chain integrated by paper, corrugated board and container manufacturers, the majority of which are SMEs in Europe. Nowadays, corrugated board containers are mostly manufactured with recycled fibres, their share being up to 82% in Europe [1]. The greatest threat faced by the mentioned production chain is related to the lack of quality of recycled fibres as raw material. Pulps made from recycled paper are generally associated with some degradation of fibre properties or more fibre breakage relative to virgin fibres, and use of recycled materials also introduces contaminants [2]. One of the most important properties of packaging paper is its mechanical strength, which depends mostly on the length of the fibres it is composed [3]. Fibres are longer in virgin pulps (those coming from papers obtained from wood, i.e. not yet recycled). However, the high pressure on their demand - as well as the current economic and ecological restrictions in the use of forest based materials - has led to a situation in which very little quantity of virgin fibre enters the recycling chain. This means that the strength quality of recycled fibres - and by projection of the papers - is constantly decreasing with the on-going recycling cycles. In addition, packaging papers present a very high variability, which constitutes an obstacle when it comes to manufacturing containers having homogeneous properties fixed by the customers at specified costs. The difficulty of predicting the properties of paper products produced from heterogeneous sources puts several limitations, which therefore lead to severe economic losses. The project RF-CORRUG Quality control of raw materials from recovered fibres for the production of corrugated board under the National Strategic Reference Framework ARCHIMEDES III deals with this common technical problem of the corrugated board industry. Specifically, the main objective of the project is to support the competitiveness of the corrugated board companies (mainly SMEs) by creating a software tool based on practical models that can predict packaging grade paper properties from data on fibres (qualitative, quantitative, morphological) used in their production. It has been shown that inherent fibre characteristics including wood species, origin, age, and chemical composition significantly influence the final properties of paper [4]. It has been also proposed that proposed that in order to predict the properties of sheets made from mixtures of pulps, the fibre characteristics of the component pulps rather than the properties of sheets made from these pulps should be used [5]. Recent studies on a variety of papers available in the market for the production of corrugated board in Spain have shown that, 6

8 besides physical-mechanical testing, fibre analysis techniques may be also used to analyse both their time-varying structure and quality [6, 7]. This papers presents information on fibres (qualitative and quantitative analysis, morphology) used for corrugated packaging production in Greece. The data will be used thereafter to develop predictive models based on advanced statistical methods for the properties and performance of packaging papers. II. M ATERIALS AND METHODS Thirty two (32) papers used by the corrugated packaging industry were used to analyse their fibre composition and morphological characteristics. The papers represent different qualities of liners (8 brown kraftliners, 8 brown testliners) and flutings-medium (8 semi chemical flutings, 8 recycled flutings) available in Greece for the production of corrugated board. The papers were provided by different paper suppliers from the global market coming from 11 European countries, Turkey, and USA. Information on the papers can be seen in Table 1. TABLE I. Paper ID Liners Flutingsmedium INFORMATION ON THE SELECTED PACKAGING GRADE PAPERS Grammage (g/m 2 ) KL France, Norway, Portugal, Switzerland, UK, USA TL Greece, Portugal, Romania, Spain, Turkey SC Bulgaria, Croatia, Finland, Romania, Sweden, Switzerland, Spain RF Greece, Portugal, Spain, Turkey Origin Classification 1 1 according to [8] Brown kraftliner: predominantly made from primary kraft pulp Brown testliner: predominantly recycled fibre based, substance equal or over 120 g/m 2 Semi chemical fluting: predominantly made from semi chemical primary fibres pulp Recycled fluting medium: predominantly recycled fibre based, substance equal or over 100 g/m 2 Qualitative and quantitative determination of the fibre components of the papers as regards the method of processing (chemical, mechanical, rag, semi-chemical and chemimechanical pulp) was carried out according to the Herzberg staining test method ISO : 1990 [9]. Maceration was possible after boiling in water of small paper pieces and shaking in glass tubes. Microscope slides were prepared with fibres according to ISO : 1990 [10]. After their staining with the Herzberg stain, fibres were viewed and systematically counted under an Eclipse 50i light microscope equipped with a digital Sight DS-5M-L1 camera (both Nikon). The fibres were classed into softwood, hardwood and nonwood fibre categories based on their morphology [11]. Weight percentages of different fibre categories were calculated by using predetermined weight factors recommended by ISO : 1990 [10]. Fibre morphology of papers was evaluated by a MorfiTrac device (MFA-5000 Morphology Fiber & Shive Analyzer, BTG Sales) in duplicate samples of 1 g solids in 600 ml of water. The disintegration of the paper materials was made by an adaptation of ISO : 2004 [12]. For obtaining the parameters of fibres (fibre morphology, curl, kink, fines, etc.) the following standards were followed: TAPPI T 233 cm-06 [13], T 234 cm-02 [14], and T 261 cm-00 [15]. III. RESULTS AND DISCUSSION A. Origin of fibres and weight percentages Microscopical identification of fibre components in pulp is a difficult task which involves several constrains. These are associated with the absence of morphological features employed in solid wood identification and the presence of similar species that are closely related in anatomical structure in the pulp mix. Also, the degradation (cutting and shortening, tearing, fibrillation, etc.) of fibres due to processing and repeated recycling puts additional restrictions. Therefore, the identification was limited to softwood and hardwood genera while nonwood components were grouped to the grasses, leaf and bast fibres, and cotton categories (Figure 1). Fig. 1. Examples of different fibre types identified in the papers: softwood and hardwood fibres (a), Pinus (b), Abies (c), Betula (d), Populus (e), cell component (spiral vessel element) of a grass pointed with arrow and cotton pointed with dashed arrow (f) All paper grades were highly variable containing different wood and nonwood components (Table 2). Kraftliners and semi chemical flutings, predominantly made from primary fibres pulp, were less variable as compared to the recycled based papers, testliners and recycled flutings. Softwood fibres of Pinus and Larix or Picea were found in abundance in all papers. All other genera (Abies, Pseudotsuga, Tsuga) were present in small amounts. The major hardwood component in the papers was fibres of Betula followed by Populus and Eucalyptus. Fagus and Tilia were also frequently observed in testliners and semichemical flutings, respectively. Due to the recycling process, other hardwood genera such as Acer, Alnus, 7 a

9 Castanea, Nyssa, Liriodendron, Liquidambar, and Quercus were identified in the papers but in very small numbers. Finally, all papers contained nonwood fibres in small amounts. Similar results showing a highly variable fibre furnish of the European packaging grade papers were reported previously [16]. Hardwood was the main fibre component of flutings (66.99% and 65.23% per weight in semi chemical and fluting papers, respectively) and testliners (61.69%), while softwood fibres with a weight percentage of 56.31% dominated in kraftliners (Table 3). Nonwood fibres were found to be a significant weight fraction in the papers, especially in the recycled flutings with a mean weight percentage of 8.58%. As expected, chemical pulp was the most important component in kraftliners (60.85%) and semi chemical pulp in semi chemical flutings (73.46%). Chemical pulp was as low as 30.10% in testliners as a result of the high amounts of recycled fibres used in their production, while the share of the two pulp types was almost equal in the recycled flutings. The results on the quantitative analysis are comparable with the weight percentages of fibre components (origin and pulping methods of fibres) for representative papers used for the production of corrugated board in Spain [6, 7] and Europe [16]. TABLE II. OCCURRENCE OF SOFTWOOD, HARDWOOD AND NONWOOD FIBRES IN THE PAPERS 1 Fibre Liners Flutings-medium categories/ Genera KL TL SC RF Softwood Abies * * - * Picea or Larix ** ** ** ** Pinus ** ** ** ** Pseudotsuga * * * * Tsuga * * * * Hardwood Acer * * * * Alnus - * * * Betula ** ** ** ** Castanea - * - - Eucalyptus * ** * ** Fagus * ** * * Nyssa * Liriodendron * * * * Liquidambar - * * * Populus * ** ** ** Tilia - * ** * Quercus * - - * Nonwood Grasses, leaf, bast * * * * Cotton * * * * 1 based on visual estimation of the relative amounts of different earlywood tracheids for softwoods, vessel elements for hardwoods, and fibres and associated cells for nonwood components ** frequent occurrence: high or moderate numbers of the different fibre types * less frequent occurrence: small or very small numbers of the different fibre types The results on fibre composition reflected the differences in quality between the paper grades. The stiffer kraftliners, being less variable and having generally higher softwood and chemical pulp contents, represent better qualities of linerboard than the testliners. The exclusive use of recycled fibres in the production of recycled flutings places them as the most variable grade from both qualitative and quantitative standpoints. TABLE III. WEIGHT PERCENTAGES OF FIBRE COMPONENTS IN THE PAPERS 1 Fibre Liners Flutings-medium categories KL TL SC RF Origin of fibres 2 Softwood (14.63) (9.89) (12.76) (7.05) Hardwood (13.93) (7.12) (12.18) (7.09) Nonwood 4.80 (2.02) 5.12 (4.44) 3.38 (2.83) 8.58 (1.81) Types of pulp 3 Chemical (5.89) (20.18) (12.64) (3.64) Semi chemical and chemi (5.89) (20.18) (12.64) (3.64) mechanical 1 mean values and standard deviations in parenthesis 2 based on their morphology 3 based on the colour reactions of fibres stained by the Herzberg stain. Mechanical and rag types of pulp were regarded as traces as their percentages were less than 2% in all papers B. Fibre morphology TABLE IV. MORPHOLOGY OF FIBRE COMPONENTS IN THE PAPERS 1 Fibre properties Liners Flutings-medium KL TL SC RF Fibre length, mm Arithmetic 0.75 (0.11) 0.49 (0.01) 0.63 (0.11) 0.51 (0.03) Length weighted 1.68 (0.27) 1.05 (0.03) 1.01 (0.10) 1.12 (0.09) Weight weighted 2.49 (0.27) 1.78 (0.08) 1.42 (0.12) 1.90 (0.25) Fibre width, µm (2.11) (0.32) (0.80) (0.61) Cell wall thickness, µm 6.20 (0.49) 5.42 (0.19) 5.72 (0.43) 5.66 (0.13) Cross sectional area, μm² (40.25) (19.91) (45.27) (11.95) Fibre volume index, 106 μm³ 0.64 (0.13) 0.35 (0.01) 0.36 (0.05) 0.37 (0.01) Coarseness, mg/m 0.20 (0.02) 0.19 (0.01) 0.16 (0.02) 0.18 (0.01) Curl, % (0.64) (1.12) 9.48 (2.04) (0.84) Kink index, l/m (155.3) (162.3) (201.6) (126.1) Fibrillation, % (2.50) (0.97) (2.11) (1.42) Fines, % (3.55) (1.07) (7.53) (2.34) Fibres per mg 6,659 (1,506) 10,858 (106) 10,217 (1,602) 10,635 (531) 1 mean values and standard deviations in parenthesis As a result of the diverse raw materials used for their production, the different paper grades varied greatly in the morphological characteristics of fibre components (Table 4). TABLE V. DISTRIBUTION OF FIBRE LENGTH FRACTIONS IN THE PAPERS Paper ID/ Distribution, % 8

10 Fibre length type KL mm mm mm mm mm mm Arithmetic Length weighted Weight weighted TL Arithmetic Length weighted Weight weighted SC Arithmetic Length weighted Weight weighted RF Arithmetic Length weighted Weight weighted Kraftliners, containing a significant amount of larger and thicker softwood fibres, had the highest fibre dimensions. Especially, the length weighted length, which is directly correlated to paper properties [17], had a mean value of 1.68 mm and was much higher than the values mm in the other grades. Semi chemical flutings, composed mainly by hardwood fibres, had the lowest coarseness mean value than the other grades. The stiff hardwood fibres were also provided semi chemical flutings with high mean fibre width (24.16 mm). Kink, curl, fibrillation and fine content were higher in the recycled grades than the respective virgin based within the liners and flutings categories. This was due to refining and beating during the repeated recycling cycles, which also helped to straighten the fibres at some extent. Fibrillation increases the bonding ability of recycled fibres but there is a limit [18]. Fines adversely affect paper structure and properties [19] but as all the grades incorporate recycled fibres in their furnish it was rational to find relatively high fines content values, especially in the recycled based testliners (33.94%) and recycled flutings (33.17%). Fibre population is associated positively to a great number of fibre and paper properties [20], but this parameter when viewed alone cannot explain the differences in paper quality. For example, kraftliners have fewer fibres per mg (6,659) than the testliners (10,858) but their quality is better. The structural differences of the papers were reflected by the quantitative distribution of fibre length (arithmetic, length weighted, weight weighted) fractions in the range mm (Table 5). The percentage of fines was represented by the fibre class mm. Arithmetically, the share of fines is quite high in all papers, especially the recycled based. However, the quantity of fines is not related directly to paper properties but rather to bonding of the fibre network [21]. The dominant fibre class in all papers was the class mm, especially in semi chemical flutings which are composed mainly by virgin hardwood fibres with lengths falling within this range. The small fibre class mm has a major contribution in testliners and recycled flutings, which are mostly made by fibres reduced in length by repeated recycling. Fibre class mm has a significant share in all papers, while the large fibre classes mm and mm were found in higher percentages in kraftliners due to the high presence of softwood fibres. IV. CONCLUSIONS The compositional analysis (qualitative, quantitative) and morphological characterisation of fibre components of packaging grade papers provided essential information on the recycled raw materials used in their production. Such diagnostics assessing the potential quality distribution of fibres available for the production of liners and flutings are highly needed to utilize the available heterogeneous resources in an optimal manner. The reliable characterisation of raw pulp materials is not only useful for a continuous control of packaging fibre sources but can be also used to evaluate the influence it has on the final properties and performance of paper products. ACKNOWLEDGMENT This research has been co-financed by the European Union (European Social Fund ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: ARCHIMEDES III. Investing in knowledge society through the European Social Fund. REFERENCES [1] FEFCO European database for corrugated board life cycle studies. FEFCO, Brussels, Belgium. [2] Ince, P. J Fibre Resources. USDA Forest Service, Madison, WI, USA, Published by Elsevier Ltd. [3] Howard, R. C The effects of recycling on pulp quality. In R. W. J. McKinney (ed.) Technology of Paper Recycling, pp Blackie Academic and Professional, London. [4] Lumiainen, J., Oy, S.D.V Refining of ECF and TCF bleached Scandinavian softwood kraft pulps under the same conditions. Paperi Ja Puu-Paper & Timber 79(2): [5] G?rres, J., Amiri, R., Wood, J. R., Karnis, A The apparent density of sheets made from pulp blends. Tappi Journal 79(1): [6] Adamopoulos, S Quantification of softwood, hardwood and nonwood fibres in packaging grade papers. Tappi Journal 5(3): [7] Adamopoulos, S., Oliver, J-V Fibre composition of packaging grade papers as determined by the Graff "C" staining test. Wood and Fibre Science 38(4):

11 [8] CEPI Containerboard European Corrugated Base Papers List. Brussels, Belgium, 22 pp. [9] ISO : Paper, board and pulps. Fibre furnish analysis - Part 3: Herzberg staining test. [10] ISO : Paper, board and pulps. Fibre furnish analysis - Part 1: General method. [11] Ilvessalo-Pflaffli, M-S Fibre Atlas - Identification of papermaking fibres. Springer series in wood science, Sprinnger-Verlag Berlin Heidelberg. [12] ISO : Pulps - Laboratory wet disintegration - Part 1: Disintegration of chemical pulps. [13] TAPPI T 233 cm-06. Fiber length of pulp by classification. [14] TAPPI T 234 cm-02. Coarseness of pulp fibers. [15] TAPPI T 261 cm-00. Fines fraction by weight of paper stock by wet screening. [16] Adamopoulos, S., Passialis, C., Voulgaridis, E Fibre characteristics of papers used in European corrugated packaging industry. In Proceedings of the 5th CTP/PTS Packaging Paper and Board Recycling International Symposium, March 18-19, Grenoble, France. Paper No.12, 10 p. [17] Clark, J.d'A Pulp Technology and Treatment for Paper, 2nd ed. Miller Freeman, San Francisco. [18] Kang, T., Paulapuro, H Effect of external fibrillation on paper strength. Pulp & Paper Canada 107(7/8): [19] Xintong, L Print mottle of wood-containing paper: The effect of fines and formation. Doctoral Thesis, Department of Chemical Engineering and Applied Chemistry, University of Toronto, Canada. [20] Foelkel, C The eucalyptus fibers and the kraft pulp quality requirements for paper manufacturing. Eucalyptus Online Books and Newsletter. Assessed on line on July 29, 2013 [21] Paavilainen, L Importance of particle size - fiber length and fines - for characterization of softwood kraft pulp. Paperi ja Puu 72(5):

12 Εφαρμογή Καινοτόμου Τεχνολογίας Παραγωγής Εμποτισμένης Ξυλείας Μαύρης Πεύκης και Οξιάς με Εφαρμογή Φυσικών Ελαίων Καραστεργίου Σωτήριος, Μπιρμπίλης Δημήτριος Τμήμα Σχεδιασμού και Τεχνολογίας Ξύλου και Επίπλου ΤΕΙ ΘΕΣΣΑΛΙΑΣ ΚΑΡΔΙΤΣΑ 43100, ΕΛΛΑΔΑ Περίληψη Στην παρούσα εργασία εξετάστηκε η συμπεριφορά εμποτισμένης με φυσικό έλαιο (κραμβέλαιο) ξυλείας μαύρης πεύκης και οξιάς μετά από έκθεση της σε εξωτερικές συνθήκες για αρκετούς μήνες. Εφαρμόστηκαν διαδοχικά πέντε προγράμματα εμποτισμού με συνεχείς τροποποιήσεις των παραμέτρων ώστε να καταδειχθεί στο τέλος η βέλτιστη μέθοδος εμποτισμού με κραμβέλαιο για κάθε είδος ξυλείας. Λέξεις κλειδιά εμποτισμός,φυσικά έλαια, πεύκη, οξυά I. ΕΙΣΑΓΩΓΗ Με το προτεινόμενο ερευνητικό έργο υιοθετείται μια καινοτόμος διαδικασία προληπτικού χειρισμού των επίπλων εξωτερικού χώρου με μίγμα φυσικών ελαίων και συντηρητικών σε περιβάλλον κενού, παράλληλα προς την εφαρμογή κατάλληλης μεθόδου συναρμολόγησης και συγκόλλησης της ξύλινης κατασκευής και εφαρμογής της τελικής επικάλυψης του επίπλου. Στόχος του συνολικού προγράμματος είναι η αναζήτηση του αποτελεσματικότερου δυνατού συνδυασμού ελαίων, συγκολλητικής ουσίας, είδους ξύλου και μεθόδου εμποτισμού, συγκόλλησης και επάλειψης των στρώσεων επικάλυψης των επίπλων, ώστε να επιτευχθεί ο βέλτιστος δυνατός εμποτισμός των ξύλινων στοιχείων με φυσικά έλαια, μειώνοντας σημαντικά το φαινόμενο της ρίκνωσης και διόγκωσης και καθιστώντας το έπιπλο μια διαστασιακά πολύ σταθερή κατασκευή. Με αυτόν τον τρόπο θα παραχθούν έπιπλα εξωτερικού χώρου, τα οποία δε θα επηρεάζονται από τις πολύ συνηθισμένες για το μεσογειακό κλίμα εναλλαγές των κλιματικών συνθηκών, θα έχουν σταθερές διαστάσεις, θα είναι το ίδιο εύκολα στο χειρισμό τους καθόλη η διάρκεια του χρόνου και το κυριότερο δε θα απαιτούν συχνή συντήρηση και βαφή. Το προτεινόμενο ερευνητικό έργο περιλαμβάνει το χειρισμό πριστής ξυλείας μαύρης πεύκης και οξυάς με επιλογή από διαλύματα διαφόρων ελαίων φυσικής προέλευσης όπως έλαιο ελαιοκράμβης, ελαιόλαδο (πυρηνέλαιο), λινέλαιο, κ.α., και αποδεκτών συντηρητικών ξύλου, σε περιβάλλον κενού και χαμηλής πίεσης, με σκοπό να μειωθεί η υγροσκοπικότητα του ξύλου, να αυξηθεί η ακρίβεια και σταθερότητα των διαστάσεων και να αποτραπεί η προσβολή του ξύλου από μύκητες και έντομα. Παράλληλα θα διερευνηθεί και η δυνατότητα συγκόλλησης του εμποτισμένου ξύλου. Στο 1 ο Πακέτο εργασίας («Ανάπτυξη καινοτόμου τεχνολογίας εμποτισμού πριστής ξυλείας με φυσικά έλαια σε πρόγραμμα διπλού κενού και μικρής πίεσης») διερευνάται η δυνατότητα εμποτισμού ελληνικής ξυλείας μαύρης πεύκης (Pinus nigra) και οξιάς (Fagus sylvatica) με φυσικά έλαια (κραμβέλαιο rape oil). Ο εμποτισμός πραγματοποιήθηκε σε ειδικό εργαστηριακό θάλαμο εμποτισμού (Εικ. 1) που διαθέτει το Εργαστήριο Τεχνολογίας Ξύλου του Τμήματος Σχεδιασμού και Τεχνολογίας Ξύλου και Επίπλου, του ΤΕΙ Θεσσαλίας. Εικ. 1. Θάλαμος εμποτισμού ξυλείας (Τμήμα Σχεδιασμού και Τεχνολογίας Ξύλου Επίπλου, ΤΕΙ Θεσσαλίας). II. ΠΕΙΡΑΜΑΤΙΚΌΣ ΣΧΕΔΙΑΣΜΌΣ Στη συγκεκριμένη πειραματική προσπάθεια μελετήθηκε η συγκράτηση ελαίου (oil retention) του ξύλου οξιάς και μαύρης πεύκης το οποίο εκτέθηκε σε εξωτερικές κλιματικές συνθήκες (Εικ. 2 και Εικ. 3). Για τον προσδιορισμό της συγκράτησης ελαίου (oil retention) σε εμποτισμένη με έλαια ξυλεία οξιάς και μαύρης πεύκης, η οποία εκτέθηκε σε εξωτερικές κλιματικές συνθήκες, ακολουθήθηκε η διαδικασία που περιγράφεται παρακάτω. 11

13 πρίση - πλάνισμα - γώνιασμα δοκιμίων με τελικές διαστάσεις 5 x 5 x 100cm, μέτρηση βάρους των δοκιμίων, υπολογισμός του όγκου (μέτρηση αρχικών διαστάσεων), υπολογισμός της περιεχόμενης υγρασίας, υπολογισμός της πυκνότητας, εμποτισμός με κραμβέλαιο, επανειλημμένη ζύγιση των δοκιμίων με ζυγό ακριβείας, και υπολογισμός της συγκράτησης ελαίου με τη βοήθεια του ακόλουθου τύπου: όπου: ΟR = (M2-M1) / V OR = συγκράτηση ελαίου, σε kg/m 3, M2 = βάρος δείγματος μετά τον εμποτισμό, σε kg, M1 = βάρος δείγματος πριν τον εμποτισμό, σε kg, και V = όγκος δείγματος πριν τον εμποτισμό, σε m 3. πίεσης, άδειασμα του κραμβελαίου, τελικό κενό 0,5bar για 15min, και εξαγωγή ξύλινων δοκιμίων. Πείραμα 2 ο : εισαγωγή ξύλινων δοκιμίων στο θάλαμο και ερμητικό κλείσιμο αυτού, εφαρμογή αρχικής πίεσης 1,2bar για 15min, γέμισμα του θαλάμου με κραμβέλαιο για 2,5min, αύξηση της πίεσης στα 5bar και διατήρηση αυτής για 45min, αφαίρεση πίεσης, άδειασμα του κραμβελαίου, τελικό κενό 0,5bar για 15min, και εξαγωγή ξύλινων δοκιμίων. Με τη μέθοδο αυτή το τελικό κενό σε συνδυασμό με την αρχική πίεση (του αέρα στις κυτταρικές κοιλότητες), βοηθά την έξοδο του πλεονάζοντος ελαίου από το ξύλο. Η αρχική πίεση γέμισε με αέρα τις κυτταρικές κοιλότητες του ξύλου, με αποτέλεσμα να εξωθείτε από αυτές το έλαιο κατά το στάδιο της εισαγωγής του. Πείραμα 3 ο : εισαγωγή ξύλινων δοκιμίων στο θάλαμο και ερμητικό κλείσιμο αυτού, εφαρμογή αρχικού κενού 0,5bar για 15min, γέμισμα του θαλάμου με κραμβέλαιο για 1min, αύξηση της πίεσης στα 5bar και διατήρηση αυτής για 45min, αφαίρεση πίεσης, άδειασμα του κραμβελαίου, τελικό κενό 0,5bar για 30min, και εξαγωγή ξύλινων δοκιμίων. Με τη μέθοδο αυτή το αρχικό κενό βοηθά στο να εισχωρήσει το έλαιο στις κυτταρικές κοιλότητες. Το τελικό κενό βοηθά την έξοδο του πλεονάζοντος ελαίου από το ξύλο. Εικ. 2. Εμποτισμένα με κραμβέλαιο δοκίμια οξιάς και μαύρης πεύκης. Εικ. 3. Δοκίμια οξιάς και μαύρης πεύκης εκτεθειμένα σε εξωτερικές κλιματικές συνθήκες. Τα πέντε προγράμματα εμποτισμού που εφαρμόστηκαν πάνω στην ξυλεία περιγράφονται αναλυτικά ως εξής: Πείραμα 1 ο : εισαγωγή ξύλινων δοκιμίων στο θάλαμο και ερμητικό κλείσιμο αυτού, εφαρμογή αρχικού κενού 0,5bar για 15min, γέμισμα του θαλάμου με κραμβέλαιο για 1min, αύξηση της πίεσης στα 5bar και διατήρηση αυτής για 45min, αφαίρεση Πείραμα 4 ο : εισαγωγή ξύλινων δοκιμίων στο θάλαμο και ερμητικό κλείσιμο αυτού, εφαρμογή αρχικής πίεσης 0,3bar για 30min, γέμισμα του θαλάμου με κραμβέλαιο για 3min, αύξηση της πίεσης στα 5,5bar και διατήρηση αυτής για 45min, αφαίρεση πίεσης, άδειασμα του κραμβελαίου, τελικό κενό 0,6bar για 30 min, και εξαγωγή ξύλινων δοκιμίων. Με τη μέθοδο αυτή το τελικό κενό σε συνδυασμό με την αρχική πίεση (του αέρα στις κυτταρικές κοιλότητες), βοηθά την έξοδο του πλεονάζοντος ελαίου από το ξύλο. Η αρχική πίεση γέμισε με αέρα τις κυτταρικές κοιλότητες του ξύλου, με αποτέλεσμα να εξωθείτε από αυτές το έλαιο κατά το στάδιο της εισαγωγής του. Πείραμα 5 ο : Με βάση τα προηγούμενα αποτελέσματα πραγματοποιήθηκε το 5ο πείραμα. Για κάθε είδος ξύλου ξεχωριστά ακολουθήθηκε διαφορετικό πρόγραμμα ξήρανσης. Το πρόγραμμα ξήρανσης που ακολουθήθηκε για την οξιά περιελάμβανε τα ακόλουθα στάδια: εισαγωγή ξύλινων δοκιμίων στο θάλαμο και ερμητικό κλείσιμο αυτού, εφαρμογή αρχικής πίεσης 0,3bar για 30min, γέμισμα του θαλάμου με κραμβέλαιο για 3min, αύξηση της πίεσης στα 3bar και διατήρηση αυτής για 25min, αφαίρεση πίεσης, άδειασμα του κραμβελαίου, τελικό κενό 0,6bar για 30 min, και εξαγωγή ξύλινων δοκιμίων. Το πρόγραμμα ξήρανσης που ακολουθήθηκε για τη μαύρη πεύκη περιελάμβανε τα ακόλουθα στάδια: εισαγωγή ξύλινων δοκιμίων στο θάλαμο και ερμητικό κλείσιμο αυτού, εφαρμογή αρχικής πίεσης 0,3bar για 30min, γέμισμα του θαλάμου με κραμβέλαιο 3min, αύξηση της πίεσης στα 3,5bar και 12