植鞣劑簡介
Wattle Extracts
(Vegetale Tannin Extracts)
很多朋友喜歡植鞣革，我也寫過介紹植鞣革的文章，現在我要把植物鞣劑，也是俗稱的栲膠給大家介紹一下。
植鞣劑是一種天然的多元酚羥基的有機物，化學分子式是C76H53O46,也可以稱為鞣酸Tannin Acid，或是單寧酸，外觀是淺黃棕色到深棕色的不定形粉狀物。很多水果未成熟時都有單寧酸，我們喝的茶葉也是有單寧酸，但是未必可以鞣製皮革。
有些地方把植物鞣劑叫做樹皮粉，或是樹膏，其來有自，因為它們是由樹皮提煉出來的。植物鞣劑用量最大的一種叫做米磨砂Mimosa，也有人叫做荊樹皮栲膠，最早的種植地是澳大利亞，後來英國人引進到南非大量種植，因為這種樹長的快，木頭可以做傢俬及船木，有經濟價值。荊樹英文學名為Acacia ，屬於含羞草科，因為它的葉子長的像含羞草。也有很多人叫它做金合歡木，因為這些樹會開黃金色的花，有一些開白色的花，這樣的就叫銀合歡木。目前全世界在南半球非洲及南美洲產量最多，英文通稱為Wattle.
植物鞣劑一般屬於非常苦澀astringent 的弱酸性的粉狀物體，通常是從木材廠中脫下的樹皮，經過蒸餾過程，變成液體，然後用噴粉乾燥 Spray Dry方式製造。通常市場上賣的植物鞣劑，有效的鞣酸成分在70%左右，價格在一千多美元一噸，受到氣候變化影響，價格會浮動。
植鞣劑不只是單用在植鞣皮，因為它有很好的染色及填充效果，所以也廣泛使用在鉻鞣牛皮的水廠複鞣過程中，可能在鉻鞣皮用量上，還比在植鞣皮多些，畢竟目前為止，市場的主要皮革還是以鉻鞣為主。
現在做植鞣牛皮的工廠，大部分都用轉鼓來鞣製，所以都會用粉狀鞣酸，但是還有一些工廠用古法製作，就是在水池浸鞣 Pit Tan方式，從幾星期到幾年都有，為了降低成本，除了用Mimosa外，他們會出去收購樹皮，用機器打碎後，然後再放入鞣皮水池，增加單寧濃酸度，英國有一家有160年歷史的皮革廠，目前還有用這種方法生產直鞣牛皮。
除了米磨砂Mimosa外，還有其他的植鞣劑，如栗木栲膠 Chestnut ，因為可以使皮革比較緊實，用在重革（底革）上面也是不少，還有堅木栲膠Quabracho,可以使皮革產生Burnish燒焦變色的效果，其他還有檳榔栲膠Gambier，染色性強，以及塔拉Tara（灌木）用在汽車座墊革製藥工業。
上面。
但是，使用量最大的植物鞣製劑，還是屬於Mimosa，大部分是由南非及巴西等地供應。
– [ ] 備註；植物單寧。除了用在皮革工藝外，也可以用在食品及藥物方面。
Vegetable Tanning Introduction
Wattle Extracts (Vegetable Tannin Extracts)
Many people are fond of vegetable-tanned leather, and I have written articles on it before. Now, let me introduce you to vegetable tanning agents, also commonly known as wattle extracts.
Vegetable tanning agents are natural organic compounds rich in polyphenolic hydroxides, with the chemical formula C76H53O46. They are also known as Tannin Acid or tannic acid. They appear as an amorphous powder ranging from light yellow-brown to dark brown. Many unripe fruits contain tannic acid, as does tea; however, these are not necessarily suitable for tanning leather.
Some regions refer to vegetable tanning agents as “bark powder” or “tree gum,” as they are extracted from tree bark. The most widely used type is called Mimosa, also known as acacia bark tannin. Originally cultivated in Australia, it was later massively planted in South Africa by the British due to its fast growth and economic value in furniture and shipbuilding. The scientific name for the wattle tree is Acacia, and it belongs to the Mimosa family. It is also referred to as the golden wattle tree due to its golden flowers; those with white flowers are known as silver wattles. Currently, the largest producers are in the Southern Hemisphere, in Africa and South America, collectively known as Wattle.
Vegetable tannins are generally a very astringent, weakly acidic powdery substance. They are usually produced from tree bark stripped at lumber mills, distilled into a liquid, and then spray-dried. The effective tannic acid content in commercial vegetable tanning agents is around 70%, with prices fluctuating around a thousand dollars per ton, influenced by climate changes.
Vegetable tannins are not just used for vegetable-tanned leather. Due to their excellent dyeing and filling properties, they are also extensively used in the retanning process of chrome-tanned leather. In fact, their usage might be higher in chrome-tanned leather, as the market mainly consists of chrome-tanned products.
Factories producing vegetable-tanned leather nowadays mostly use drum tanning, so powdered tannins are generally used. However, some still use the traditional pit tanning method, which can take from several weeks to years. To reduce costs, aside from using Mimosa, they also purchase tree bark, crush it with machinery, and then add it to the tanning pits to increase tannic acid concentration. In the UK, there is a 160-year-old leather factory still using this method to produce vegetable-tanned leather.
Besides Mimosa, other vegetable tannins include Chestnut, used for making leather more compact and often used in heavy leather. Quabracho creates a burnish or scorched color effect, while Gambier is highly staining, and Tara is used in the automotive and pharmaceutical industries.
Note: Vegetable tannins are not only used in leather craftsmanship but also in the food and pharmaceutical industries.
資料來源https://www.facebook.com/leatherandmylife
圖片來源:https://www.carlfriedrik.com/int/magazine/vegetable-tanned-leather
