スギ (Cryptomeria japonica D. Don) 樹皮の燃料資源的基礎研究

概要

論文の詳細を見る
わが国における未利用樹皮は年間に約800万<special>m3</special>に達している。この樹皮は地域的エネルギー確保対策上，燃料として活用することが、最もも妥当であると考えられる。そこで，未利用樹皮の成型燃料化を図るため、樹皮の現存量，排出量，物理化学的性質及び燃料的性質に関する一貫した基礎的研究を三重大学農学部附属平倉演習林のスギ人工林において実施した。その結果は次の通りである。 1 スギ樹皮の現存量（1）各林齢における標準木の樹皮平均乾重は，10年生 1.3kg，20年生 3.2kg，30年生 5.2kg，40年生 7.2kg，60年生 19．4kgであった。（2）各標準木の乾重とそれぞれの林分におけるha当り立木本数にもとづく ha当りの樹皮現存量は，上記林齢の順に，5.4t，7.4t，9.7t，10.7t，16.Otと推定され，林齢別における樹皮現存量は総現存盈の6～7％を占め林齢にかかわりはなくほぼ一定であった。（3）樹幹部の樹皮率は上記林齢の順に，乾重比では11.7％，11.0％，9.2％，8.5％ 8.9％容積比では13.1％，7.0％，5.8％，5.7％，5.0％，対樹幹容積重量比では<special>40.7kg/m3，35.3kg/m3，30.8kg/m3，28.1kg/m3，31.2kg/m3</special>　であった。（4）樹幹樹皮量と胸高直径との間には，<special>LogY4＝-2.269+2.459LogX（r2=0.975）</special>の関係が認められた。（5）熊野地方のスギ収穫表と本研究で得られた単木樹皮率とにもとづいて，平倉演習林の林分樹皮現存量を推定し，実測値と比較した。その結果，平倉演習林の若齢林では，収穫表から推定された数値より多く，また，平倉演習林の壮齢林では，収穫表にもとづく地位Ⅰと地位Ⅲに対する推測値の中間の値となることが認められた。2 スギ樹皮の物理化学的性質（1）スギ樹幹樹皮の内樹皮率は林齢によって変化しており，壮齢樹になるほど減少する傾向がある。靭性，粘着性に富む内樹皮の存在率と粉砕性とは相関性があり，内樹皮率の低い壮齢樹樹皮は若齢樹樹皮より粉砕し易い。また磁製ポール。ミルによる砕製物は，Rosin-Raillmlerの粒度分布則に適合していた。（2）気乾粉末樹皮の温水抽出率は4.3～14.5％であり，生活機能を有しまた低分予フラバノールの多い内樹皮の存在率が高い若齢樹樹皮は，壮齢樹樹皮より抽出率が高い傾向がある。しかし，1％NaOHによる抽出率は31.3～28.7％であって，温水抽出率ほど林齢による傾向は明確でない。なお，同一林齢の樹皮抽出には，大きな個体差が認められた。（3）樹皮の温水抽出物のpHは3.8～5.2の範囲にあって，一般的な樹種の木質部と同様弱酸性を示し，また緩衝容数は0.15～0.20mol/100gであった。しかし陽イオン交換樹脂を用いて脱塩処理することによって，抽出物のpHは2.9～3.1となり緩衝容量も0.21～0.33mol/100gに増加する。即ち樹皮の酸性度は，含有するアルカリ金属またはアルカリニ土類金属の量に依存していると見なされる。（4）利用研究の活潑なカラマツ（Larix leptolepis）樹幹樹皮の抽出物は，スギ樹皮抽出物と類似した性質を有しているが，抽出率はスギ樹皮の約2倍であった。したがって，樹皮抽出物中のフェノール性成分の活用，または圧縮成型加工による固型燃料化を目的とした場合は，カラマツ樹皮の方が優れていると推定される。 3 スギ樹皮の燃料的性質（1）10～60年の範囲では樹齢にかかわらず，外樹皮の発熱量は4.900～4.950cal/gである。内樹皮の発熱量はばらつきが大きいが，外樹皮のそれより，おおよそ300cal/g低い。（2）10～20年生の若齢木の樹幹樹皮は 4.800cal/gを示し，樹齢とともに増し，60年生樹皮では4.930cal/gに達して，おおむね一定となる。これは，内・外樹皮の組成割合によって結果され，新生する内樹皮量と剥落する外樹皮量がほぼ平衡に達すると考えられるからである。（3）温抽出こよって樹皮の発熱量は低下するが，今回の実験では温水抽拇率がほぼ一定に達した樹齢（30～60年）の樹幹樹皮についての測定であるので，その低下は150～190cal/gの範囲にとどまった。（4）40年生スギ（樹高17.55m）の樹幹樹皮の発熱量は地際部において最も高く，約 4.800cal/gで，地上高が増すと緩やかに下り，地上高15～16m部においては，約4.680cal/gである。Eight million cubic meters of tree bark were disposed without any use every year in Japan. Of many means of potential utilization, it is most practical to use bark as fuel in industry and at home as the local energy. To make this in reality a fundamental survey of biomass of stem bark (above ground), physicochemical nature and thermal quality of the stem bark in Sugi (Cryptomeria japonica D.Don) forest, were investigated in the selected normal stands at the age of 10, 20, 30, 40, and 60 years in Mie University Forest.1. Dry biomass of Sugi stem bark (1) Mean dry weight of the stem bark of a sample tree in the 10, 20, 30, 40, and 60 year stand were 1.3, 3.2, 5.2, 7.2, and 19.4 kg, respectively. (2)Dry biomass of the stem bark per unit area (ha) in each stand can be obtained on a basis of dry weight of the stem bark of a sample tree and the tree density a unit area.The stem bark to the total biomass in each age stand was 5.4t/87.2t in 10 year sand,7.4t/101.8t in 20, 9.7t/148.4t in 30, 10.7t/175.1t in 40, 16.0t/222.4t in 60 and expressed in the precentage as 6.2, 7.3, 6.5, 6.1, 7.2%, respectively, thus the bark ratio to the stem in a unit area in each stand is about constant, regardless of stand age. (3) As the tree age increased, the percent of the stem bark to the stem per a sample tree, either on volume or on dry weight, decreased. (4) Allometric relations between D.B.H. and each part of a sample tree (Stem, Living leaves, Living branches, and Bark) were examined and the following regressions are obtained :Stem : <special>Log Y₁　= -1.729 + 2.844 Log X (r2=0.987)</special>Living leaves : <special>LogY₂　= -0.6615 + 1.307 Log X (r2=0.818)</special>Living branches : <special>Log Y₃　= -1.393 + 1.792 Log X (r2=0.857)</special>Bark : <special>Log Y₄　= -2.269 + 2.459 Log X (r2=0.975)</special> Here <special>Y₁</special> is each part of a sample tree in kg, X is D.B.H.in cm. The stem bark biomass in University Forest were estimated by the mean D.B.H of the stand, using the above allometric relations and agreed well with those measured. (5) Stem bark biomass of a young stand (10 year) in University Forest was greater than the values that were estimated by the product of the bark percent and the mean volume of the same age stand in the yield table for KUMANO-area in Mie prefecture. In thrifty stand (60 year) in University Forest, however, the bark biomass was intermediate between an estimated value from the yield table for KUMANO-aria for the site classⅠand that for the site class Ⅲ.2. Physicochemical properties of Sugi stem bark (1) The weight ratio of the inner bark to the whole bark of Sugi stems was varied with the ages of the stand and had a tendency to decrease with the age advanced. So the proportions of the inner bark, which have more toughness and tackiness than the outer barks, relate to the reducing property into powder of the samples, that the barks from the old aged trees could be ground easily than the youngers. The powder of the barks prepared by using a porcelain ball mill was followed the Rosin-Rammler distribution law, like as the other kinds of crushed materials. (2) The hot-water extractives of the air-dried powder of the barks were contained in a range from 4.3 to 14.5% and those from the youngers generally showed the higher values, because of the higher proportions of the inner bark which possessed vital functions and contained the low molecular flavanols. The contents of the 1% sodium hydroxide extractives ranging from 21.3 to 28.7%, houever, could not show any definite propensity to the stand ages. Furthermore, tree to tree differences in the quantities of the extractives within the same age stand were very wide so that the variations among the individual trees in the physical and the chemical properties should be taken into consideration to the practical use. (3) The aqueous extractives of the barks exhibited weak acidic nature ranging in pH from 3.8 to 5.2, which were similar to those in the extractives from a common wood. The buffering capacity, which yielded a simplified parameter of the acidity for the water extractives, was 0.15 to 0.20 mol/100g. By pretreatment with a cation-exchange resin, however, the pH values of all the extractives were found to lie between 2.9 and 3.1 and their buffering capacities increased to be 0.21 to 0.33 mol/100 g. These behavior is attributed to the content of alkali and alkaline earth- metals in the sample. (4) The chemical properties of the extractive of Karamatsu (Larix leptolepis) stem bark,which has been studied by many investigators for the effective utilization, were similar to but the quantities of the extractives about twice of those of the Sugi bark. From these results, Karamatsu bark is assumed to be of greater advantage than Sugi bark, in utilizing phenolic components in the bark or in making the solid fuel by the pressure molding.3. Fuel values of Sugi stem bark (1) The stem bark between 1.2 and 3.2 m high above ground was first air-dried and pulverized by a Wiley-mill equipped with a 12 mesh shieve. The heat value for the air-dried bark powder and its residue extracted with a hot-water was determined by the calorimeter and shown as cal/g of oven-dried sample. a) The heat values for the outer bark are in a range of 4900-4,950 cal/g. Those for the inner bark are rather fluctuated and about 300 cal/g less than those for outer bark. b) The heat values for the stem barks on young trees in a stand of 10 to 20 years exhibit about 4,800 cal/g. The values for the barks are gradually increasing with a tree age advanced and finally approaching an uppermost ones of 4,930 cal/g. This is due to a ratio of the inner bark to the whole bark : an amount of a newly developed inner bark tissue is about equal to that of a naturally falling down bark scale. c) Hot-water extraction reduces the potential heat value in bark as much as 150-190 cal/g in compared with the corresponding unextracted bark from the stem of 30-60 year trees. (2) The heat value of the bark in a tree at a different height above ground is determined using the bark on the stem-disks at a certain interval, which are originally used for the analysis of the stem volume, in a 40-year tree in a height of 17.55 m. The heat value for the stem bark is highest in lower part of 4,800 cal/g, decreases very slightly with the height advanced from ground and reaches about 4,680 cal/g in an upper part of 15-16 m high. 4. Potential heat value of the stem bark in Sugi plantation. The fundamental survey for the potential biomass in a from of the stem bark was carried out in the sample stands in the ages of every 10 years except 50 in Sugi plantation in Mie University Forest. The heat values of the stem bark in each stand are found, in a unit of <special>106 kcal/ha</special>, as 26 in 10 year stand, 35 in 20 year, 47 in 30 year, 52 in 40 year, and 79 in 60 year. An example way the heat value of the stem bark in 60 year stand is equivalent to those from the fuel kerosene of 50 drums containing 200 liters. Considering the stem bark is practical which would be disposed in following works in the wood industry after felling and yarding. Thus, the stem bark is an important potential for the local energy source in the rural forest industry areas.
1983-10-01

著者

島地岩根
三重大生物資源演習林

スギ (Cryptomeria japonica D. Don) 樹皮の燃料資源的基礎研究

スポンサーリンク

概要

著者

関連論文

スポンサーリンク