ヒノキ (Chamaecyparis obtusa SIEB. et ZUCC.) 樹皮の燃料資源的基礎研究

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森林未利用資源の一つである樹皮の成型燃料化を図り，ローカルエネルギーとして活用するために，樹皮の現存量及び諸性質に関する一貫した基礎研究を三重大学農学部附属平倉演習林のヒノキ人工林において実施した。その結果は以下の通りである。　1 ヒノキ樹皮の現存量（1）各林齢における標準木の樹皮平均乾重は，10年0.298kg，15年0.893kg，20年1.533kg，30年4.203kgであった。（2）林齢齢の標準木樹皮平均乾重及びha当り立木本数にもとづく ha当り樹皮現存最は，10年1.5t，15年4.2t，20年6.9t，25年8.6t，30年10.3tと推定され，生育環境が劣悪であった20年生林分を除く林齢別樹皮現存量は，総現存量の6～7％を占め林齢にかかわり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，18.8％，13.87％，19.06％，1l.31％，10.90％，容積比では，14.68％，13.65％，19.69％，10.44％，12.86％，対樹幹容積重量比では，<special> 73.38kg/m3，58.84kg/m3，72．42kg/m3，46．37kg/m3，46.13kg/m3 </special>であった。（4〉ヒノキ標準木の幹・葉・枝・樹皮の乾重と胸高直径との間にほっきりとした相対成長則がみとめられ，樹幹樹皮量と胸高直径との間には <special>　LogY4=-1.164＋2.428LogX（r2＝0.975）</special>　の関係式を得た。　2 ヒノキ樹皮の物理化学的性質及び成型性（1）ヒノキ樹幹樹皮の内樹皮率は林齢によって変化しているが，樹高1.2～3.2mの部位の内樹皮率ほ42～68％であり，スギ樹皮より僅か高い数値を示した。ヒノキ樹皮の粉砕性は使用粉砕機の機種によって異なり，ウイレー・ミルではスギ樹皮より微粉化しやすかったが，ボール・ミルでは極めて困難であった。　（2）ヒノキの気乾樹皮粉末の温水及び1％NaOH抽出率はそれぞれ12.4～20.77％及び42．5～51.5％であり，スギ樹皮の場合の約2～3倍であった。またpHは4.0～4.4の範囲にあってスギ樹皮より僅か強い酸性度を示した。（3）樹皮の成型性を推定するため，スギ，ヒノキ及びカラマツのウイレー・ミル粉砕樹皮から成型板を製造し，それぞれの平面引張り強さを測定した。その結果，抽出物含量の高かったヒノキ及びカラマツ樹皮の成型性がスギ樹皮より優れていること，及びスギ樹皮成型板の強度に対するスギ外樹皮部の寄与率が高いことが示された。　3 ヒノキ樹皮の熱的性質（1）ヒノキ樹幹樹皮・剥皮した生枝・生葉の気乾微粉末（80メッシュ通過）を毎回, 2～3mg用いて空気中で600℃まで10℃/minで昇温し，熱分析（T，TG，DTG，DTA同時記録）を行った。　a）試料に吸着していた水分の蒸散によって60℃辺りにピークをもつ吸熱曲線（DTA）がえられ，約10％の重量減少（TG）を記録した。　b）200℃附近から熱分解が始り320～330℃を中心とする第1の発熱ピークがDATにみられ，約50％の重量減少を来たし，同時に残留物の炭化が進行する。　C）第1の発熱ピークをもつDTA曲線は380℃附近から第2の発熱反応に転じ，急激な，時に燃焼を伴う，発熱反応を示し，420～450℃にピークが現れこの間に30％前後の重量減少がみられ，500℃で概ね熱分解を終了し，数％の灰を残す。　　d）ヒノキ生薬の粉末においては，第2ピークが420～430℃にみられ，その終り頃に第3の小さい発熱ピークが465～470℃に現われ，500℃で終了する。　幹の上部の若い樹皮は熱分解がやや低温域より始まる。又，未成熟材である生枝は，熱分析曲線よりみる限りその熱分解は樹皮と殆んど変らない。（2）地上高1.2～3.2m間の樹幹樹皮のウイレー・ミルによる砕製物（気乾）について，断熱熱量計によって発熱最を測定し絶乾試料1g当りの値（Cal/g）に換算した。　a）調査した10～30年生ヒノキ樹幹樹皮については4,900～5,055cal/gで同林齢のスギ樹皮より100～250cal/g高かった。最高は15～20年生の樹皮にみられ5040～5055cal/gであった。　b）温水抽出によって13～19％に及ぶ或種の組成分が失われ，明らかに原樹皮より林齢に関係なく，約150cal/g程度の熱量を低下する。　C）ヒノキ30年生A標準木の樹幹樹皮の地上高による熱量分布についてはスギ樹幹樹皮におけるような一般的な傾向は見出せなかった。For the utilization of the stem bark of Hinoki as a local energy, a fundamental study of the biomass, and the physicochemical nature and thermal quality of the stem bark was carried out in Mie University Forest.1. Dry biomass of Hinoki stem bark (1) Mean dry weight of the stem bark for the Hinoki sample tree in the 10, 15, 20, 25 and 30 year stands were 0.298, 0.893, 1.533, 2.661 and 4.203kg. (2) The biomass of the stem bark to the total in a unit area (ha) in each stand was 1.5t/25.3t in the 10 year, 4.2t/56.5t in the 15, 6.9t/72.7t in the 20, 8.6t/120.8t in the 25 and 10.3t/142.8t in the 30 year Hinoki stand ; the percentages were 5.9, 7.4, 9.5, 7.1 and 7.2%, respectivery. The bark ratios for Hinoki stands are almost the same at 6 to 7% regardless of stand age, except that of the 20 year stand of Hinoki which was due to the poor site condtions. (3) The percent of stem bark to the stem per a sample tree, were ca. 10-20% either on dry weight or on volume. As the stand age increased, these bark percentages decreased. (4) Allometric relation 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= -1,828 + 2,965 Log X (r2=0,996)</special> Living leaves : <special>LogY2　= -0,630 + 1,259 Log X (r2=0,935)</special> Living branches : <special>Log Y3　= -0,853 + 1,353 Log X (r2=0,903)</special> Bark : <special>Log Y4　= -1,164 + 2,428 Log X (r2=0,975)</special>　Here, Yί is each part of a sample tree in kg, X is D.B.H in cm.2. Physicochemical and molding properties of Hinoki stem bark　(1) The weight ratio of the inner bark to the whole bark on Hinoki stems was varied with the ages of the stand.The proportions of the inner bark in stem barks between 1.2 and 3.2 m leves in living trees were 42 to 68 %. They were a little higher than those of Sugi barks which showed the values ranging from 34 to 61 %. The reducibility into powder of the samples was different by a type of pulverizer. By a Wiley mill,the barks from all Hinoki trees tested could be ground easily than Sugi barks. But, inconvenient result was showed for the grinding of Hinoki bark in the case of the using a porcelain ball mill.　(2) The hot-water and the 1% sodium hydroxide extractives of the air-dried powder of Hinoki barks were contained in a range from 12.4 to 20.7% and from 42.4 to 51.5%, respectively. These values were about twice to triple those of Sugi samples, and related to the stand ages to some extent. However, tree to tree differences in the quantities of the extractives within the same age stand were very wide like as Sugi barks, so that the variations among the individual samples in nature should be taken into consideration to the practical use. The pH values for Hinoki bark extractives ranged from 4.0 to 4.4, indicated that the acidity was slightly higher than Sugi bark.　(3) To evaluate the molding property, the boards were made from Sugi, Hinoki and Karamatsu bark powders prepared by a wiley mill and the tensile strength perpendicular to the surface of the boards was measured. From the results it appears that the stem barks on Hinoki and Karamatsu trees having much larger quantities of the extractivies were of great advantage than Sugi bark in making the solid fuel by the pressure molding. Furthemore, an important contribution of the outer bark to the strength of Sugi whole bark was also demonstrated. 3. Thermal properties of Hinoki stem bark　(1) Two to three mg of an air-dried fine powder of Hinoki stem bark at a certain height, lived twigs and lived leaves were thermally analyzed using the Mettler thermoanalyzer type I upto 600℃ by raising temperature of 10°/min under static atmosphere and the curves for T, TG, DTG, DTA were recorded simultaneously.a) Aroud 60℃, an endothermic peak was observed due to loss of the absorved water and about 10% weight loss was recorded.b) Thermal degradation of the substance started around 200℃ and the first exothermic peak was observed at around 320-330℃. During this pyrolytic stage about 50% of the weight of material was decomposed and concomitantly the remaining skeleton of the wood substance was rearanged to carbonize.c) The second exothermic reaction, which was vigoros and firing sometimes, began from around 380℃ and reached the peak at around 420-450℃. During this stage about 30% of sample weight was lost and the pyrolysis was ended about 500℃ with the ash of several percents remained.d) The case of the lived leaves, nearly end of the above c) stage, however, a small third exothermic peak was added and ended at about the same 500℃ as the other materals. A young bark covered the upper trunk was decomposed a little easily. A lived twing debarked which was composed mostly juvenile xylem tissue was fundamentally exhibited the same thermal curves as the stem bark. (2) A calorie was determined by means of a bomb calorimeter using the pulverized bark or twing flour and expressed as cal/g of an oven-dried material. The heat values were 4,900-5,055 cal/g for Hinoki stem bark in the height of 1.2-3.2m above ground of 15-30 year stand. The highest value was obtained around 15-20 year stand with the 5,040-5,055 cal/g. In general, Hinoki bark has 100-250 cal/higher calorific value than that of Sugi. The extraction with hot-water lost some extractives and resulted in a reduction of caloric by around 150 cal/g. The fuel value distribution in a bole bark at different height was not observed in any definit pattern.
1984-12-01

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島地岩根
三重大生物資源演習林

ヒノキ (Chamaecyparis obtusa SIEB. et ZUCC.) 樹皮の燃料資源的基礎研究

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