JP3752776B2 - POLYLACTIC ACID COMPOSITION, PROCESS FOR PRODUCING THE SAME, AND MOLDED ARTICLE OF THE COMPOSITION - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、衣料用、日用生活用、医薬品材料用、医療材料用、および農業、漁業、工業、建築土木等の産業資材用に利用できる、粉末、繊維、フィルム、および成形材料として好適なポリ乳酸組成物の製造方法に関する。
【０００２】
【従来の技術】
化石原料由来の合成ポリマーに対して、ポリ乳酸は穀物を発酵させて得られる乳酸を原料とするため、地球資源保護の観点から注目されている。また、ポリ乳酸は土中、水中および生体内で容易に加水分解され、自然界に広く存在し動植物に対して無害な乳酸となり、最終的には代謝あるいは微生物分解によって二酸化炭素と水とに分解されるため、生分解性材料としても注目されている。更に近年は、特に生体に対する安全性が高いことから、医薬、医療分野への応用が盛んに行われている。
【０００３】
ポリ乳酸の合成法としては、乳酸をオリゴマー化した後、これを解重合して環状二量体であるラクチドを単離し、このラクチドを溶融開環重合させて得る方法が知られている。この方法は、ラクチドの精製を充分に行いさえすれば比較的容易に高分子量のポリ乳酸が得られるため、非常に有用な方法である。
【０００４】
このラクチド溶融開環重合の触媒としては種々の金属化合物が報告されているが、中でもスズ化合物、特にオクチル酸スズ（以下、Ｓｎ（Ｏｃｔ）2 と略記する）がその触媒活性の高さから、短い重合時間で高分子量のポリ乳酸が得られるため好ましく用いられている。
【０００５】
【発明が解決しようとする課題】
本発明が解決しようとする課題は、第一にポリ乳酸の熱安定性の改善であり、第二に成形加工時の揮発成分による周辺環境汚染の防止を目的とするポリ乳酸中の残存ラクチドの低減である。
【０００６】
まず、第一の課題について詳述する。ポリ乳酸は他の熱可塑性プラスチックと同様、加熱溶融による成形加工が可能である。しかし、Ｓｎ（Ｏｃｔ）2 を触媒として製造されたポリ乳酸は成型加工工程にて著しく分子量が低下し、充分な強度を持つ成形品が得られないという問題点がある。その原因は加水分解、解重合および環状オリゴマー化並びに分子内および分子間エステル交換によるもので、このような反応にポリ乳酸中に残存するスズ化合物が関与していることが知られている。
【０００７】
この解決策として幾つかの方法が提案されている。例えば、ポリ乳酸重合生成物を水に対して不混和性の有機溶媒に溶解し、次いで無機酸、水溶性有機酸又は水溶性錯化剤を含む水性相又は水と接触させ、該有機相を分離した後ポリ乳酸を公知の方法で単離することで触媒を除去する方法（特開昭６３−１４５３２７号）、該重合生成物を親水性有機溶媒の存在下、酸性物質と接触させることにより触媒を除去する方法（特開平７−１０２０５３号）、あるいは該重合生成物にホウ素化合物を添加し、触媒を失活させることで熱安定性を改善する方法（特開平７−６２２１３号）等が挙げられる。
【０００８】
しかし、第１、第２の方法は多量の溶媒と労力、設備を必要とするためコスト面で不利となり、またポリ乳酸中に浸透した溶媒の完全な除去が難しい等のため、品質面での問題点も多い。また、第３の方法は重合生成物であるポリマーチップに微量の添加剤を均一に分散させることは非常に難しく、この分散に溶媒を使用した場合はその除去に関して問題が生じることは前記第１、第２の方法と同様である。
【０００９】
すなわち、重合生成物を後処理を加えずにそのまま次の成型加工工程に用いることが工業的には理想であるが、Ｓｎ（Ｏｃｔ）2 触媒を用いたラクチド溶融開環重合でこれを達成するのは困難である。
【００１０】
一方、Ｓｎ（Ｏｃｔ）2 以外の触媒によるポリ乳酸重合の研究は数多くなされているが、得られた重合生成物の熱安定性の観点から触媒を検討した例は無い。
【００１１】
本発明にて用いたトリスアセチルアセトナトアルミニウム（以下、Ａｌ（Ａｃａｃ）3 と略記する）がラクチドの溶融開環重合に際して触媒作用を有することはＭａｋｒｏｍｏｌ．Ｃｈｅｍ．、１９９１、２２８７〜２２９６、（１９９６）に記載されている。同文献によれば、ラクチドに対して０．１モル％のＡｌ（Ａｃａｃ）3 を用い１５０℃で５０時問重合させることにより重量平均分子量（Ｍｗ）１７．１万（数平均分子量（Ｍｎ）９万、Ｍｗ／Ｍｎ＝１．９より算出）のポリ乳酸が得られている。
【００１２】
上記の例を工業化する場合に問題となる点は、まず第一に重合時間がかかりすぎることである。この問題点を解消する手段として容易に考えられる方法は、重合温度を上げることと触媒量を増やすことである。ところが、ラクチド溶融開環重合によるポリ乳酸重合の場合、ラクチドとポリ乳酸の間に重合平衡が存在し、その温度が高いほど平衡はラクチド側になることから、重合温度を高くするほど重合度が上がりにくくなることが知られている。また、触媒量に関してもスズ化合物その他の触媒研究の結果、その量を増やせば増やすほど重合度は低下することが当業者間での常識となっている。よって、前記の例の重合条件に対して、重合温度をあげる、あるいは触媒量を増やす等の操作を行った場合、得られるポリ乳酸の分子量は前記例の値よりもさらに低いものになると考えられていた。これらがＡｌ（Ａｃａｃ）3 が高分子量のポリ乳酸を得るためのラクチド溶融開環重合触媒として工業的使用に適さないと判断されていた所以である。
【００１３】
次に第二の課題について詳述する。ポリ乳酸をラクチドの溶融開環重合で製造した場合、重合生成物中にラクチドが残存するのを避けることはできない。この残存ラクチドは成形加工時に気化し、周辺環境の汚染、成形金型の汚染、成形品中のボイド形成による強度低下等の原因となる。ポリ乳酸にラクチドが残存する原因は、モノマー（ラクチド）／ポリマー間の重合平衡により１５０℃以上ではモノマーは０にはならないからである。
【００１４】
このラクチドを重合生成物から除く方法として提案されているものとして、特開平３−１４８２９号公報に記載の方法が挙げられる。同方法はラクチドの開環重合による生体吸収性ポリエステル製造の後半あるいは反応終了後に重合生成物を溶融状態に保ちながら減圧し、残存ラクチドを系外に除くというものである。
【００１５】
上記公報には開環重合に使用する触媒および触媒量に関する特定はないが、実施例に記載されているのは前と同様にＳｎ（Ｏｃｔ）2 でその使用量はラクチドに対して０．０００８６〜０．００３２モル％の範囲である。しかし上記範囲の触媒量では工業的に妥当な時間で重合を完了させることは難しい。例えば、該公報の実施例９にはＬ−ラクチドに対して０．００２４モル％のＳｎ（Ｏｃｔ）2 を用いた例が開示されているが、２００℃で常圧下１８０時間、さらに減圧下で２時間と非常に長い重合時間を必要としている。
【００１６】
一方、Ｓｎ（Ｏｃｔ）2 の量を増やすと重合速度は上昇するが、同時に解重合速度も大きくなり、減圧によってラクチドを除いてもすぐに再生産されるため残存ラクチド量は低下せず、又そのまま減圧を続ければポリマー収率が低下してしまう。
【００１７】
従って、Ｓｎ（Ｏｃｔ）2 触媒によるポリ乳酸重合において、減圧によるラクチド除去を工業的に実施が可能な条件で行なうことは困難であった。
【００１８】
本発明は上記の実情に鑑みなされたものであって、第一の課題に対しては高分子量でかつ熱安定性に優れるため成形加工時の分子量低下が小さく、高強度の成形品を与えるポリ乳酸組成物、ラクチド溶融開環重合において重合後の後処理を必要としない高分子量かつ熱安定性に優れたポリ乳酸組成物の新規な製造方法、および該ポリ乳酸組成物からなる成形品の提供を目的とするものである。
【００１９】
また、第二の課題に対しては成形加工時の周辺環境汚染が無いポリ乳酸組成物、残存ラクチド量の少ないポリ乳酸組成物を短時間で効率よく製造する方法、および該ポリ乳酸組成物からなる成形品の提供を目的とするものである。
【００２０】
【課題を解決するための手段】
上記第一の目的を達成するための本発明は、乳酸の環状二量体であるラクチドを溶融開環重合してポリ乳酸を製造するに際し、触媒として該ラクチドに対して０．１５〜４．０モル％のＡｌ（Ａｃａｃ） 3 を用いることを特徴とするポリ乳酸組成物の製造方法である。
【００２４】
又、第二の目的を達成するための本発明は、乳酸の環状二量体であるラクチドを溶融開環重合してポリ乳酸を製造するに際し、触媒として該ラクチドに対して０．１５〜４．０モル％のＡｌ（Ａｃａｃ）3 を用い、重合系中の残存ラクチド量が３０〜５％となるまで重合反応を進行させる第一工程と、該工程の重合生成物を溶融状態で減圧下におき重合を完結させる第二工程とからなることを特徴とするポリ乳酸組成物の製造方法である。
【００２６】
【発明の実施の形態】
本発明に用いられるラクチドは前述したように乳酸をオリゴマー化した後解重合することによって得られる乳酸の環状二量体である。乳酸にはＬ−乳酸とＤ−乳酸が存在し、それに伴ってラクチドにもＬ−ラクチド、Ｄ−ラクチド、Ｄ、Ｌ−ラクチド、ラセミラクチドが存在する。本発明に用いられるラクチドの光学純度は特に限定されるものではないが、得られる高分子量ポリ乳酸の融点はポリ乳酸の光学純度によって決定され、高純度のものほど高融点のポリ乳酸が得られるため、より耐熱性の高いポリ乳酸を望むならば高光学純度のラクチドを用いることが好ましい。
【００２７】
ラクチドの溶融開環重合においては水酸基を有する化合物が重合の開始剤として働くため、生成するポリ乳酸の分子量は原料中の水酸基濃度によって決定される。例えば、ホモポリマーの場合、重量平均分子量２０万以上のポリ乳酸を得るためには原料中の水分量は５ｐｐｍ〜６０ｐｐｍの範囲内にあることが必要である。
【００２８】
本発明に用いられるＡｌ（Ａｃａｃ）3 は前述したようにその使用量がラクチドに対して０．１モル％では十分な分子量のポリ乳酸は得られない。しかし、本発明者等は該Ａｌ（Ａｃａｃ）3 が当業者の常識に反して、その使用量を増やすことで得られるポリ乳酸の分子量が増大することを見出した。本発明におけるＡｌ（Ａｃａｃ）3 の使用量は、ラクチドに対して０．１５〜４．０モル％（ポリ乳酸の乳酸単位にたいしては０．０７５〜２．０モル％）である。０．１５モル％未満では得られるポリ乳酸の分子量が充分ではなく、使用量が増えると得られるポリ乳酸の分子量は大きくなるが３．０モル％付近で分子量の増加が飽和し、それ以上ではむしろ分子量が低下する。また、Ａｌ（Ａｃａｃ）3 の使用量増加に伴って得られたポリ乳酸の熱安定性は低下する傾向にあり、４．０モル％より多く使用することは熱安定性の点からも不利である。
【００２９】
本発明における重合温度は特に限定されるものではないが、１８０〜２００℃であることが好ましい。１８０℃より低温では重合に長時間を要するとともに、得られたポリ乳酸の融点よりも低温であるため攪拌が不能となり好ましくない。また、２００℃より高温ではラクチドとポリ乳酸の平衡がラクチド側に偏りすぎるため重合度が上がりにくくなり、またラクチドの生成量が増大するためポリ乳酸の収率が低下する。
【００３０】
重合生成物中の残存ラクチドを低減させる手段として、重合をある程度まで進行させる第一工程と、その重合生成物から減圧によってラクチドを除去する第二工程とに分けて行なうことが望ましい。該第一工程の終点は重合生成物中の残存ラクチド量が３０〜５％に達した時点である。残存ラクチド量が３０％より多い時点で第一工程を終了させると、残ったラクチドは第二工程にて除かれるわけであるからポリマー収率は７０％より小さくなり不経済である。また第一工程終了時の残存ラクチド量が５％未満であれば、第二工程にて十分ラクチドが除去されない。これは残存ラクチドが重合生成物中で可塑剤として作用し、減圧下での自身の揮発を助けていると考えられる。
【００３１】
第一工程に要する時間は通常は６０〜６００分であるが使用した触媒の量、重合温度、系内の水分量などによって異なるため、系中の残存ラクチド量をチェックしてその時間を適宜選択すればよい。又、第一工程を実施するための重合装置は特に限定されるものではないが、例えば攪拌装置と加熱機構を備えたバッチ式反応容器、あるいはエクストルーダータイプの連続式反応装置等を挙げることができる。ただし、前述したように本反応は系中の水分量によって生成するポリ乳酸の重合度が左右されるため、反応系は無水雰囲気下であることが望ましく、窒素、アルゴン等の不活性ガス雰囲気下で重合させることが望ましい。
【００３２】
上記第一工程で得られる重合生成物を第二工程に移行させる方法は得に限定されるものではないが、その間も重合生成物は無水雰囲気下にあることが好ましい。従って、例えば不活性ガスでシールされたバッチ式反応容器中で第一工程を行なった場合には、重合生成物を反応容器外に取り出さず、そのまま系を減圧にして第二工程を行なうのが望ましい。また、連続反応装置で第一工程を行なった場合には、その取り出し口から第二工程へ無水雰囲気下で直接移送するか、あるいは取り出した後無水雰囲気下で貯蔵し、しかる後第二工程に移すという方法を挙げることができる。
【００３３】
本発明の第二工程は、第一工程で得られた重合生成物中の残存ラクチドを低減させる工程であり、その終点とするところは残存ラクチドの量が１％未満となった時点が好適に選ばれる。第二工程の温度条件は重合生成物の融点以上であることが必須である。例えば、ポリＬ乳酸ホモポリマーの場合には１８０℃以上であることが必要である。また、その上限は前述のように２００℃以下である事が好ましい。２００℃より高温にするとポリ乳酸の解重合速度が上昇し、いくら減圧によってラクチドを除いてもラクチドが再生産することにより終点に達しない虞がある。また減圧の条件は特に限定されるものではないが、減圧度は低ければ低いほど終点に達するまでの時間が短縮されるため、好ましくは１０ｍｍＨｇ以下、より好ましくは５ｍｍＨｇ以下である。
【００３４】
本発明の製造方法で得られるポリ乳酸組成物を溶融成形して成形品を得ることができる。前記成形品の例としては射出、押し出し等の各種成形品、フィルム、シ−トまたは未延伸もしくは延伸配向された繊維、さらには前記繊維からの繊維構造物（編物、織物、不織布、紙、紐、テ−プ、ロ−プ、網など）、さらには合成皮革の様な前記フィルムやシートと繊維との複合物が挙げられるがこれらに限定されるものではない。
【００３５】
これら成形品の用途としては、防虫、保温、防霜、遮光、防草用フィルム、シ−ト、繊維構造物等の農業用用途、乗り物の内装や電気製品等の工業用用途、法面緑化保護用シ−トや繊維構造物等の土木用用途、床や壁材等の建築用途、使い捨て器具、使い捨て衣料、靴や鞄等も含めた日用生活用品、玩具やゲーム機等を含めた遊具、生理用品等を含めた衛生医療用途、漁網、釣り糸、各種養殖用ロ−プ、網などの漁業用用途等が挙げられるがこれらに限定される物ではない。
【００３６】
【実施例】
以下、実施例により本発明を詳述する。なおその前に本明細書における種々の特性値の測定法を記述する。
【００３７】
＜重量平均分子量＞
クロロホルムを溶離液としたＧＰＣ（ゲル浸透クロマトグラフィー）によってポリ乳酸組成物中のポリマ−部の重量平均分子量（Ｍｗ）を測定した。なお、分子量較正曲線はポリスチレンを用いて作成した。
【００３８】
＜残存ラクチド量＞
前述のＧＰＣ測定におけるポリマー部、及びモノマー（ラクチド）部の面積から、下記式にて求められる値を重合生成物中の残存ラクチド量とした。
【００３９】
残存ラクチド量（％）＝モノマー部の面積／（ポリマー部の面積＋モノマー部の面積）×１００
【００４０】
＜曲げ強度＞
五酸化燐存在下、室温で２４時間減圧乾燥したポリ乳酸組成物を２００℃、５分の条件で圧縮成形し、厚さ約１．６ｍｍの成形板を得た。これより、幅１５ｍｍ、長さ８０ｍｍの試験片を切り出し、支点間距離２６ｍｍ、試験速度０．８ｍｍ／分の条件で曲げ強度を測定した。
【００４１】
＜物性安定性＞
成形品とした時の物性としての安定性を、次の様に成形安定性で調べた。すなわち、成形前のポリ乳酸組成物（重合後）を前述した圧縮成形法で成形した（成形後）。重合後および成形後のポリ乳酸組成物の重量平均分子量（Ｍｗ）を測定し、下記式にて成形安定性を求めた。
【００４２】
成形安定性（％）＝ポリ乳酸組成物Ｍｗ（成形後）／ポリ乳酸組成物Ｍｗ（重合後）×１００
【００４３】
また、成形品の安定性を成形作業を行う代わりに以下の方法による熱安定性で代表させた。すなわち、溶融処理前のポリ乳酸組成物（重合後）約３ｇを、試験管中窒素下で１８０℃、１時間加熱（溶融処理）し、得られたポリ乳酸組成物（溶融後）をえた。重合後と溶融後のポリ乳酸組成物の重量平均分子量（Ｍｗ）を前述の方法で測定し、下記式にて熱安定性を求めた。
【００４４】
熱安定性（％）＝ポリ乳酸組成物Ｍｗ（溶融後）／ポリ乳酸組成物Ｍｗ（重合後）×１００
【００４５】
＜収率＞
重合原料であるラクチドの重量と、重合生成物であるポリ乳酸組成物の重量から、重合反応の収率を下記式より求めた。
【００４６】
収率（％）＝ポリ乳酸組成の重量／原料の重量×１００
【００４７】
（実施例１）
Ｌ−ラクチド（水分率３１ｐｐｍ、ＰＵＲＡＣ社製）１２０ｇ（８３３ｍｍｏｌ）とＡｌ（Ａｃａｃ）3 ２．７０ｇ（８．３３ｍｍｏｌ）を、攪拌装置、窒素導入管を備えた反応容器に投入し、窒素置換の後、窒素気流下で１８０℃に加熱し溶融開環重合させた。このとき、触媒であるＡｌ（Ａｃａｃ）3 の量は、原料のＬ−ラクチドに対して１．０モル％、生成したポリ乳酸組成物の乳酸単位に対しては０．５モル％であった。分子量の上昇が飽和した時点で反応を終了し重合生成物を系外に取り出した。得られたポリ乳酸組成物およびこれを成形して得られた成形板の特性は表１に示すとおりであった。
重合後のポリ乳酸組成物の重量平均分子量は４３．２万と非常に大きく、また成形後も３２．４万（成形安定性７５．０％）の高分子量を保持しているため、成形板の曲げ強さも９９８ｋｇｆ／ｃｍ2 と非常に大きなものであった。これは触媒としてＳｎ（Ｏｃｔ）2 を用いて得られたポリ乳酸組成物成形板の曲げ強度（比較例１）の約１．６倍の値であった。
【００４８】
（比較例１）
実施例１におけるＡｌ（Ａｃａｃ）3 に代えて該ラクチドに対して０．１ｍｏｌ％のＳｎ（Ｏｃｔ）2 を触媒として用いる以外は実施例１と同様にして溶融開環重合をおこなった。得られたポリ乳酸組成物およびこれを成形して得られた成形板の特性は表１に示すとおりであった。
重合後のポリ乳酸組成物の重量平均分子量は実施例１と同様に４５．６万の高分子であったが、成形によって分子量が１２．４万（成形安定性２７．２％）まで大きく低下し、そのため成形板の曲げ強さも６２５ｋｇｆ／ｃｍ2 しかなく実施例１に比べてはるかに小さい値であった。
【００４９】
【表１】
実施例１および比較例１によるポリ乳酸組成物の溶融処理した前後の重量平均分子量を表２に示す。成形品の安定性の場合と同様に実施例１によるものが３６．５万の高分子量を保持し、熱安定性も８４．５％と高値を示すのに対し、比較例１によるものは分子量が７．８万と著しく低下し、熱安定性が１７．３％と低値を示した。この結果もＡｌ（Ａｃａｃ）3 触媒によるポリ乳酸組成物の熱安定性の高さを示すものである。また、同処理が成形のシミュレ−ションとして妥当であることを示すものである。
【００５１】
（実施例２〜６）
実施例１におけるＡｌ（Ａｃａｃ）3 の触媒量を表２のとおりにする以外は実施例１と同様にして溶融開環重合をおこなった。得られたポリ乳酸組成物の特性値は表２に示すとおりである。いずれからも重量平均分子量の大きなポリ乳酸が得られ、溶融処理後も２０万以上の重量平均分子量（熱安定性６０％以上）を保持しており、熱安定性の高いポリ乳酸組成物が得られた。
【００５２】
（比較例２）
Ａｌ（Ａｃａｃ）3 の触媒量を０．２７０ｇ（０．８３３ｍｍｏｌ）とする以外は実施例１と同様にして溶融開環重合をおこなった。このとき、Ａｌ（Ａｃａｃ）3 は、原料のＬ−ラクチドに対して０．１モル％、生成したポリ乳酸組成物の乳酸単位に対しては０．０５モル％となる。得られた重合生成物の特性値は表２に示すとおりであり、重量平均分子量が２０万以下と低値であり、本発明の方法（実施例１〜６）によって得られるものより小さかった。
【００５３】
（比較例３）
Ａｌ（Ａｃａｃ）3 の触媒量を１３．５ｇ（４１．６ｍｍｏｌ）とする以外は実施例１と同様にして溶融開環重合をおこなった。このとき、Ａｌ（Ａｃａｃ）3 は、原料のＬ−ラクチドに対して５．０モル％、生成したポリ乳酸組成物の乳酸単位に対しては２．５モル％となる。得られた重合生成物の特性値は表２に示すとおりであり、溶融処理後の重量平均分子量が２０万以下、熱安定性が５１．９％と低値であり、本発明の方法（実施例１〜６）によって得られるものより小さかった。
【００５４】
【表２】
（実施例７）
Ｌ−ラクチド（水分率１１ｐｐｍ、ＰＵＲＡＣ社製）６０ｇ（４１６ｍｍｏｌ）とＡｌ（Ａｃａｃ）3 ０．６７５ｇ（２．０８ｍｍｏｌ）を、攪拌装置、窒素導入管を備えた反応容器に投入した。このとき、触媒であるＡｌ（Ａｃａｃ）3 の量は、原料のＬ−ラクチドに対して０．５モル％であった。窒素置換の後、第一工程として窒素気流下で１８０℃に加熱し溶融開環重合させた。残存ラクチド量が約１５％になった時点で第二工程として系を３ｍｍＨｇまで減圧しさらに１８０℃で加熱、重合させた。分子量の上昇が飽和した時点で反応を終了し重合生成物を系外に取り出した。得られたポリ乳酸組成物の特性は表３に示す通りであり、Ｍｗが３６．２万で残存ラクチド量が０．１％と非常に少ないポリ乳酸組成物が４８．２ｇ（収率８０．３％）得られた。また、１８０℃で１時間溶融処理した後のＭｗは３２．４万と分子量保持率が高く、熱安定性は９０％と優れたものであった。
【００５６】
（実施例８）
実施例７において第一工程終了後に一旦窒素下で重合生成物を系外に取り出し、冷却、粉砕の後に再び反応容器に戻し、第二工程を行なった。得られた重合生成物の特性は表３に示す通りであり、実施例７と同様に高重合度で熱安定性は８８％と優れたポリ乳酸組成物が得られた。
【００５７】
（比較例４）
実施例７において第一工程をポリ乳酸組成物の分子量の上昇が飽和する時点までとし、第二工程を行なわなかった以外は実施例７と同様にして重合を行なった。得られた重合生成物の特性は表３に示す通りであり、残存ラクチド量が３．５％と非常に多いものであった。
【００５８】
（比較例５）
実施例７におけるＡｌ（Ａｃａｃ）3 に代えて、該ラクチドに対して０．１モル％のＳｎ（Ｏｃｔ）2 を用いた以外は実施例７と同様にして重合を行なった。得られたポリ乳酸組成物の特性は表３に示す通りであり、残存ラクチド量が１．８％と非常に多く、熱安定性も２１％と低いものであった。
【００５９】
【表３】
（実施例９、１０）
実施例７における第一工程を残存ラクチドが２８．３％および６．４％になるまでとした以外は実施例７と同様にして重合を行なった。得られた重合生成物の特性は表４に示す通りであり、いずれの場合も高重合度、低残存ラクチド量のポリ乳酸組成物が高収率で得られた。
【００６１】
（比較例６）
実施例７における第一工程を残存ラクチド量が３９．１％になるまでとした以外は実施例７と同様にして重合を行なった。得られた重合生成物の特性は表４に示す通りであり、第一工程終了後の残存ラクチド量が多かったため、高重合度、低残存ラクチド量の重合生成物が得られたがその収率は５５．２％と低いものであった。
【００６２】
（比較例７）
実施例７における第一工程を残存ラクチド量が４．３％になるまでとした以外は実施例７と同様にして重合を行なった。得られた重合生成物の特性は表４に示す通りであり、第一工程終了後の残存ラクチド量が少なくなりすぎたため、第二工程でのラクチド除去が十分に行われず、残存ラクチド量が２．３％となった
【００６３】
【表４】
【発明の効果】
本発明の製造方法で得られるポリ乳酸組成物は熱安定性が高いため成形加工の際の分子量が２０万以上に保持され、高強度の成形品が得られる。また、本発明の方法はラクチド溶融開環重合後の後処理を必要とせず、高分子量で熱安定性に優れたポリ乳酸組成物を得ることができるため、工業的に非常に利用価値が高い。また、触媒として従来のスズ化合物に替わりより安全なアルミニウム化合物を用いているため、生体内材科、あるいは食品関係への使用に際しても安全性が高い。また、本発明のポリ乳酸組成物は残存ラクチド量が少ないため成形加工時にラクチドが揮発し周辺環境を汚染することがなく、成形品中に残存ラクチドに由来するボイドの形成とそれに起因する低強度部分が無い成形品を得ることができる。また、本発明の方法はポリ乳酸中の残存ラクチドの除去に、再沈や洗浄等の溶媒除去工程を要する方法を用いず、重合に要する時間も短いため工業的価値が非常に高い。さらに、本発明の成形品は高強度であるため、衣料用、日用生活用、医薬品材料用、医療材料用、および農業、漁業、工業、建築、土木などの産業資材用に用いる粉末、繊維、フイルム、および成形材料として極めて好適である。[0001]
BACKGROUND OF THE INVENTION
The present invention is suitable as powders, fibers, films, and molding materials that can be used for clothing, daily life, pharmaceutical materials, medical materials, and industrial materials such as agriculture, fishery, industry, and civil engineering. It relates to the production how the polylactic acid composition.
[0002]
[Prior art]
In contrast to synthetic polymers derived from fossil raw materials, polylactic acid uses lactic acid obtained by fermenting cereals as a raw material, and thus has attracted attention from the viewpoint of protecting global resources. Polylactic acid is easily hydrolyzed in soil, water, and in vivo, and is widely distributed in nature and harmless to animals and plants. Ultimately, it is decomposed into carbon dioxide and water by metabolism or microbial degradation. Therefore, it attracts attention as a biodegradable material. Furthermore, in recent years, since the safety to living bodies is particularly high, it has been actively applied to the medical and medical fields.
[0003]
As a method for synthesizing polylactic acid, a method is known in which lactic acid is oligomerized and then depolymerized to isolate lactide, which is a cyclic dimer, and this lactide is melt-opened and polymerized. This method is a very useful method because a high molecular weight polylactic acid can be obtained relatively easily if the lactide is sufficiently purified.
[0004]
Various metal compounds have been reported as catalysts for this lactide melt ring-opening polymerization. Among these, tin compounds, particularly tin octylate (hereinafter abbreviated as Sn (Oct) 2 ), have high catalytic activity. Since high molecular weight polylactic acid can be obtained in a short polymerization time, it is preferably used.
[0005]
[Problems to be solved by the invention]
The problem to be solved by the present invention is firstly to improve the thermal stability of polylactic acid, and secondly to prevent residual lactide in polylactic acid for the purpose of preventing environmental pollution due to volatile components during molding processing. It is a reduction.
[0006]
First, the first problem will be described in detail. Polylactic acid, like other thermoplastics, can be molded by heat melting. However, polylactic acid produced using Sn (Oct) 2 as a catalyst has a problem that the molecular weight is remarkably lowered in the molding process and a molded product having sufficient strength cannot be obtained. The cause is due to hydrolysis, depolymerization and cyclic oligomerization, and intramolecular and intermolecular transesterification, and it is known that tin compounds remaining in polylactic acid are involved in such reactions.
[0007]
Several methods have been proposed for this solution. For example, the polylactic acid polymerization product is dissolved in an organic solvent immiscible with water and then contacted with an aqueous phase or water containing an inorganic acid, a water-soluble organic acid or a water-soluble complexing agent, and the organic phase is After separation, the polylactic acid is isolated by a known method to remove the catalyst (Japanese Patent Laid-Open No. 63-145327), and the polymerization product is brought into contact with an acidic substance in the presence of a hydrophilic organic solvent. A method for removing the catalyst (Japanese Patent Laid-Open No. 7-102053) or a method for improving the thermal stability by adding a boron compound to the polymerization product and deactivating the catalyst (Japanese Patent Laid-Open No. 7-62213), etc. Can be mentioned.
[0008]
However, the first and second methods are disadvantageous in terms of cost because they require a large amount of solvent, labor, and equipment, and it is difficult to completely remove the solvent that has penetrated into polylactic acid. There are many problems. Further, in the third method, it is very difficult to uniformly disperse a trace amount of additive in a polymer chip that is a polymerization product, and when a solvent is used for this dispersion, there is a problem with respect to the removal. This is the same as the second method.
[0009]
That is, it is ideal industrially to use the polymerization product as it is in the next molding process without post-treatment, but this is achieved by lactide melt ring-opening polymerization using Sn (Oct) 2 catalyst. It is difficult.
[0010]
On the other hand, many studies have been made on polylactic acid polymerization using a catalyst other than Sn (Oct) 2, but no catalyst has been studied from the viewpoint of the thermal stability of the obtained polymerization product.
[0011]
The fact that trisacetylacetonatoaluminum (hereinafter abbreviated as Al (Acac) 3 ) used in the present invention has a catalytic action in the melt ring-opening polymerization of lactide is described in Makromol. Chem. 1991, 2287-2296, (1996). According to the same literature, weight average molecular weight (Mw) of 171,000 (number average molecular weight (Mn)) is obtained by polymerizing at 150 ° C. for 50 hours using 0.1 mol% of Al (Acac) 3 with respect to lactide. Polylactic acid of 90,000, calculated from Mw / Mn = 1.9).
[0012]
The problem that arises when industrializing the above example is that it takes too much polymerization time. An easily conceivable method for solving this problem is to increase the polymerization temperature and increase the amount of catalyst. However, in the case of polylactic acid polymerization by lactide melt ring-opening polymerization, there is a polymerization equilibrium between lactide and polylactic acid, and the higher the temperature, the closer the equilibrium is to the lactide side, so the higher the polymerization temperature, the higher the degree of polymerization. It is known that it is difficult to go up. As for the amount of catalyst, as a result of research on tin compounds and other catalysts, it is common knowledge among those skilled in the art that the degree of polymerization decreases as the amount increases. Therefore, when an operation such as increasing the polymerization temperature or increasing the amount of catalyst is performed with respect to the polymerization conditions of the above example, the molecular weight of the obtained polylactic acid is considered to be even lower than the value of the above example. It was. These are the reasons why Al (Acac) 3 was judged not suitable for industrial use as a lactide melt-opening polymerization catalyst for obtaining high molecular weight polylactic acid.
[0013]
Next, the second problem will be described in detail. When polylactic acid is produced by melt ring-opening polymerization of lactide, it is inevitable that lactide remains in the polymerization product. This residual lactide is vaporized during the molding process, causing contamination of the surrounding environment, contamination of the molding die, and reduction in strength due to void formation in the molded product. The reason why lactide remains in polylactic acid is that the monomer does not become zero at 150 ° C. or higher due to the polymerization equilibrium between the monomer (lactide) / polymer.
[0014]
As a method for removing the lactide from the polymerization product, there is a method described in JP-A-3-14829. The method is to remove the residual lactide from the system by reducing the pressure while keeping the polymerization product in a molten state in the latter half of the production of the bioabsorbable polyester by ring-opening polymerization of lactide or after completion of the reaction.
[0015]
Although the above publication does not specify the catalyst used in the ring-opening polymerization and the amount of the catalyst, it is Sn (Oct) 2 as described above in the examples, and the amount used is 0.00086 with respect to lactide. It is the range of -0.0032 mol%. However, it is difficult to complete the polymerization in an industrially reasonable time with the catalyst amount in the above range. For example, Example 9 of the publication discloses an example using 0.0024 mol% Sn (Oct) 2 with respect to L-lactide, but at 200 ° C. under normal pressure for 180 hours and further under reduced pressure. A very long polymerization time of 2 hours is required.
[0016]
On the other hand, when the amount of Sn (Oct) 2 is increased, the polymerization rate increases, but at the same time, the depolymerization rate also increases. If the decompression is continued as it is, the polymer yield decreases.
[0017]
Therefore, in polylactic acid polymerization using Sn (Oct) 2 catalyst, it is difficult to remove lactide under reduced pressure under conditions that can be industrially implemented.
[0018]
The present invention has been made in view of the above circumstances, and for the first problem, it has a high molecular weight and is excellent in thermal stability. Lactic acid composition, a novel method for producing a polylactic acid composition having high molecular weight and excellent thermal stability that does not require post-treatment after polymerization in lactide melt-opening polymerization, and provision of a molded product comprising the polylactic acid composition It is intended.
[0019]
Further, for the second problem, a polylactic acid composition free from environmental pollution during molding, a method for efficiently producing a polylactic acid composition with a small amount of residual lactide in a short time, and the polylactic acid composition The purpose is to provide a molded product.
[0020]
[Means for Solving the Problems]
In order to achieve the above first object, the present invention provides a polylactic acid produced by melt-opening polymerization of lactide, which is a cyclic dimer of lactic acid. A method for producing a polylactic acid composition, wherein 0 mol% of Al (Acac) 3 is used.
[0024]
Further, 0.15 present invention for achieving the second object, upon the production of polylactic acid lactide which is a cyclic dimer of lactic melt ring-opening polymerization to, with respect to the lactide as a catalyst Using 4.0 mol% of Al (Acac) 3 , the first step of proceeding the polymerization reaction until the amount of residual lactide in the polymerization system reaches 30 to 5%, and the polymerization product of the step under reduced pressure in the molten state It is a manufacturing method of the polylactic acid composition characterized by including the 2nd process which puts down and completes polymerization.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
The lactide used in the present invention is a cyclic dimer of lactic acid obtained by oligomerizing lactic acid and depolymerizing it as described above. Lactic acid includes L-lactic acid and D-lactic acid, and accordingly, lactide includes L-lactide, D-lactide, D, L-lactide, and racemic lactide. The optical purity of lactide used in the present invention is not particularly limited, but the melting point of the high molecular weight polylactic acid obtained is determined by the optical purity of polylactic acid, and the higher the purity, the higher the melting point of polylactic acid. Therefore, if polylactic acid with higher heat resistance is desired, it is preferable to use lactide with high optical purity.
[0027]
In the melt ring-opening polymerization of lactide, a compound having a hydroxyl group works as an initiator for polymerization, and thus the molecular weight of the produced polylactic acid is determined by the hydroxyl group concentration in the raw material. For example, in the case of a homopolymer, in order to obtain polylactic acid having a weight average molecular weight of 200,000 or more, the water content in the raw material needs to be in the range of 5 ppm to 60 ppm.
[0028]
As described above, when the amount of Al (Acac) 3 used in the present invention is 0.1 mol% based on lactide, polylactic acid having a sufficient molecular weight cannot be obtained. However, the present inventors have found that the molecular weight of polylactic acid obtained by increasing the amount of the Al (Acac) 3 is contrary to the common knowledge of those skilled in the art. The amount of Al (Acac) 3 used in the present invention is 0.15 to 4.0 mol% with respect to lactide (0.075 to 2.0 mol% for the lactic acid unit of polylactic acid). If the amount is less than 0.15 mol%, the molecular weight of the polylactic acid obtained is not sufficient, and the molecular weight of the polylactic acid obtained increases as the amount used increases, but the increase in molecular weight saturates in the vicinity of 3.0 mol%. Rather, the molecular weight decreases. In addition, the thermal stability of the polylactic acid obtained with an increase in the amount of Al (Acac) 3 used tends to decrease, and using more than 4.0 mol% is disadvantageous from the viewpoint of thermal stability. is there.
[0029]
Although the polymerization temperature in this invention is not specifically limited, It is preferable that it is 180-200 degreeC. When the temperature is lower than 180 ° C., polymerization takes a long time, and since the temperature is lower than the melting point of the obtained polylactic acid, stirring is not possible, which is not preferable. Further, at a temperature higher than 200 ° C., the equilibrium between lactide and polylactic acid is too biased toward the lactide side, making it difficult to increase the degree of polymerization, and the yield of polylactic acid is decreased because the amount of lactide produced is increased.
[0030]
As a means for reducing the residual lactide in the polymerization product, it is desirable to carry out by dividing it into a first step in which the polymerization proceeds to a certain degree and a second step in which the lactide is removed from the polymerization product under reduced pressure. The end point of the first step is when the amount of residual lactide in the polymerization product reaches 30 to 5%. If the first step is terminated when the amount of residual lactide is more than 30%, the remaining lactide is removed in the second step, so the polymer yield is less than 70%, which is uneconomical. If the amount of residual lactide at the end of the first step is less than 5%, the lactide is not sufficiently removed in the second step. This is thought to be due to the residual lactide acting as a plasticizer in the polymerization product and helping to volatilize itself under reduced pressure.
[0031]
The time required for the first step is usually 60 to 600 minutes, but it depends on the amount of catalyst used, the polymerization temperature, the amount of water in the system, etc., so check the amount of residual lactide in the system and select the time as appropriate. do it. The polymerization apparatus for carrying out the first step is not particularly limited, and examples thereof include a batch type reaction vessel equipped with a stirrer and a heating mechanism, or an extruder type continuous reaction apparatus. it can. However, as described above, since the degree of polymerization of polylactic acid produced in this reaction depends on the amount of water in the system, the reaction system is preferably in an anhydrous atmosphere, and in an inert gas atmosphere such as nitrogen or argon. It is desirable to polymerize with.
[0032]
The method for transferring the polymerization product obtained in the first step to the second step is not limited to obtaining, but it is preferable that the polymerization product be in an anhydrous atmosphere during that time. Therefore, for example, when the first step is carried out in a batch type reaction vessel sealed with an inert gas, the second step is carried out by reducing the system as it is without taking the polymerization product out of the reaction vessel. desirable. In addition, when the first step is performed in a continuous reaction apparatus, it is directly transferred from the outlet to the second step in an anhydrous atmosphere, or is taken out and stored in an anhydrous atmosphere, and then the second step. The method of transferring can be mentioned.
[0033]
The second step of the present invention is a step of reducing the residual lactide in the polymerization product obtained in the first step, and the end point is preferably the time when the amount of residual lactide is less than 1%. To be elected. It is essential that the temperature condition of the second step is equal to or higher than the melting point of the polymerization product. For example, in the case of a poly L lactic acid homopolymer, it is necessary to be 180 ° C. or higher. Moreover, it is preferable that the upper limit is 200 degrees C or less as mentioned above. When the temperature is higher than 200 ° C., the depolymerization rate of polylactic acid increases, and even if the lactide is removed by a reduced pressure, there is a possibility that the end point may not be reached due to the reproduction of lactide. In addition, the conditions for reducing the pressure are not particularly limited. However, the lower the degree of pressure reduction, the shorter the time until the end point is reached, so it is preferably 10 mmHg or less, more preferably 5 mmHg or less.
[0034]
The polylactic acid composition obtained by the production method of the present invention can be melt-molded to obtain a molded product. Examples of the molded products include various molded products such as injection and extrusion, films, sheets, unstretched or stretched fibers, and fiber structures (knitted fabrics, woven fabrics, nonwoven fabrics, paper, strings) from the fibers. , Tapes, ropes, nets, etc.), and composites of the film or sheet and fibers such as synthetic leather, but are not limited thereto.
[0035]
Applications of these molded products include insect protection, heat insulation, frost prevention, shading, grass protection films, sheets, agricultural applications such as fiber structures, industrial applications such as vehicle interiors and electrical products, and slope greening. Civil engineering applications such as protective sheets and textile structures, architectural applications such as floors and wall materials, disposable appliances, disposable clothing, daily necessities including shoes and bags, playground equipment including toys and game machines Examples include, but are not limited to, hygiene and medical uses including sanitary products, fishing nets, fishing lines, various aquaculture ropes, fishery uses such as nets, and the like.
[0036]
【Example】
Hereinafter, the present invention will be described in detail by way of examples. Before that, the measurement methods of various characteristic values in this specification will be described.
[0037]
<Weight average molecular weight>
The weight average molecular weight (Mw) of the polymer part in the polylactic acid composition was measured by GPC (gel permeation chromatography) using chloroform as an eluent. The molecular weight calibration curve was prepared using polystyrene.
[0038]
<Residual lactide amount>
From the area of the polymer part and monomer (lactide) part in the GPC measurement described above, the value obtained by the following formula was used as the amount of residual lactide in the polymerization product.
[0039]
Residual lactide amount (%) = area of monomer part / (area of polymer part + area of monomer part) × 100
[0040]
<Bending strength>
The polylactic acid composition dried under reduced pressure at room temperature for 24 hours in the presence of phosphorus pentoxide was compression molded at 200 ° C. for 5 minutes to obtain a molded plate having a thickness of about 1.6 mm. From this, a test piece having a width of 15 mm and a length of 80 mm was cut out, and the bending strength was measured under the conditions of a distance between fulcrums of 26 mm and a test speed of 0.8 mm / min.
[0041]
<Physical property stability>
The stability as a physical property when formed into a molded product was examined by molding stability as follows. That is, the polylactic acid composition before molding (after polymerization) was molded by the compression molding method described above (after molding). The weight average molecular weight (Mw) of the polylactic acid composition after polymerization and after molding was measured, and molding stability was determined by the following formula.
[0042]
Molding stability (%) = polylactic acid composition Mw (after molding) / polylactic acid composition Mw (after polymerization) × 100
[0043]
The stability of the molded product was represented by the thermal stability by the following method instead of performing the molding operation. That is, about 3 g of the polylactic acid composition before the melting treatment (after polymerization) was heated (melting treatment) at 180 ° C. for 1 hour under nitrogen in a test tube to obtain the obtained polylactic acid composition (after melting). The weight average molecular weight (Mw) of the polylactic acid composition after polymerization and after melting was measured by the above-mentioned method, and the thermal stability was determined by the following formula.
[0044]
Thermal stability (%) = polylactic acid composition Mw (after melting) / polylactic acid composition Mw (after polymerization) × 100
[0045]
<Yield>
From the weight of lactide as a polymerization raw material and the weight of the polylactic acid composition as a polymerization product, the yield of the polymerization reaction was determined from the following formula.
[0046]
Yield (%) = weight of polylactic acid composition / weight of raw material × 100
[0047]
Example 1
120 g (833 mmol) of L-lactide (water content 31 ppm, manufactured by PURAC) and 2.70 g (8.33 mmol) of Al (Acac) 3 were put into a reaction vessel equipped with a stirrer and a nitrogen introduction tube, Thereafter, it was heated to 180 ° C. under a nitrogen stream and subjected to melt-opening polymerization. At this time, the amount of Al (Acac) 3 as the catalyst was 1.0 mol% with respect to the raw material L-lactide and 0.5 mol% with respect to the lactic acid unit of the produced polylactic acid composition. . When the increase in molecular weight was saturated, the reaction was terminated and the polymerization product was taken out of the system. Table 1 shows the characteristics of the obtained polylactic acid composition and the molded plate obtained by molding the composition.
The weight average molecular weight of the polylactic acid composition after polymerization is as extremely large as 432,000, and it retains a high molecular weight of 34,000 (molding stability 75.0%) after molding. The bending strength of was 998 kgf / cm 2 and was very large. This was about 1.6 times the bending strength (Comparative Example 1) of the polylactic acid composition molded plate obtained using Sn (Oct) 2 as a catalyst.
[0048]
(Comparative Example 1)
Melt ring-opening polymerization was carried out in the same manner as in Example 1 except that 0.1 mol% of Sn (Oct) 2 was used as a catalyst in place of Al (Acac) 3 in Example 1. Table 1 shows the characteristics of the obtained polylactic acid composition and the molded plate obtained by molding the composition.
The weight average molecular weight of the polylactic acid composition after the polymerization was a high molecular weight of 46,000 as in Example 1. However, the molecular weight was greatly reduced to 124,000 (molding stability 27.2%) by molding. Therefore, the bending strength of the molded plate was only 625 kgf / cm 2 , which was much smaller than that of Example 1.
[0049]
[Table 1]
Table 2 shows the weight average molecular weights before and after the melt treatment of the polylactic acid composition according to Example 1 and Comparative Example 1. As in the case of the stability of the molded product, the one according to Example 1 retains a high molecular weight of 365,000 and the thermal stability is as high as 84.5%, whereas the one according to Comparative Example 1 has a molecular weight. Was significantly reduced to 78,000, and the thermal stability was as low as 17.3%. This result also shows the high thermal stability of the polylactic acid composition by the Al (Acac) 3 catalyst. This also shows that this process is appropriate as a molding simulation.
[0051]
(Examples 2 to 6)
Melt ring-opening polymerization was carried out in the same manner as in Example 1 except that the catalyst amount of Al (Acac) 3 in Example 1 was changed as shown in Table 2. The characteristic values of the obtained polylactic acid composition are as shown in Table 2. Polylactic acid having a large weight average molecular weight can be obtained from any of the above, and a polylactic acid composition having a high heat stability can be obtained, having a weight average molecular weight of 200,000 or more (heat stability of 60% or more) even after melt treatment It was.
[0052]
(Comparative Example 2)
Melt ring-opening polymerization was carried out in the same manner as in Example 1 except that the catalyst amount of Al (Acac) 3 was changed to 0.270 g (0.833 mmol). At this time, Al (Acac) 3 is 0.1 mol% with respect to L-lactide as a raw material, and 0.05 mol% with respect to the lactic acid unit of the produced polylactic acid composition. The characteristic values of the obtained polymerization product are as shown in Table 2, the weight average molecular weight was as low as 200,000 or less, and was smaller than that obtained by the method of the present invention (Examples 1 to 6).
[0053]
(Comparative Example 3)
Melt ring-opening polymerization was carried out in the same manner as in Example 1 except that the catalyst amount of Al (Acac) 3 was changed to 13.5 g (41.6 mmol). At this time, Al (Acac) 3 is 5.0 mol% with respect to the raw material L-lactide and 2.5 mol% with respect to the lactic acid unit of the produced polylactic acid composition. The characteristic values of the obtained polymerization product are as shown in Table 2. The weight average molecular weight after the melt treatment is 200,000 or less, and the thermal stability is as low as 51.9%. Less than that obtained by Examples 1-6).
[0054]
[Table 2]
(Example 7)
60 g (416 mmol) of L-lactide (water content 11 ppm, manufactured by PURAC) and 0.675 g (2.08 mmol) of Al (Acac) 3 were put into a reaction vessel equipped with a stirrer and a nitrogen introduction tube. At this time, the amount of Al (Acac) 3 as a catalyst was 0.5 mol% with respect to L-lactide as a raw material. After nitrogen substitution, as a first step, melt ring-opening polymerization was performed by heating to 180 ° C. under a nitrogen stream. When the amount of residual lactide reached about 15%, the system was decompressed to 3 mmHg as a second step, and further heated and polymerized at 180 ° C. When the increase in molecular weight was saturated, the reaction was terminated and the polymerization product was taken out of the system. The characteristics of the obtained polylactic acid composition are as shown in Table 3. 48.2 g of polylactic acid composition having an Mw of 36,000 and a residual lactide amount of 0.1% (yield: 80. 2 g). 3%). Moreover, Mw after melt-processing at 180 degreeC for 1 hour was 324,000 and the molecular weight retention rate was high, and heat stability was as excellent as 90%.
[0056]
(Example 8)
In Example 7, after completion of the first step, the polymerization product was once taken out of the system under nitrogen, cooled and ground again, and then returned to the reaction vessel to perform the second step. The characteristics of the obtained polymerization product are as shown in Table 3. As in Example 7, a polylactic acid composition having a high degree of polymerization and an excellent thermal stability of 88% was obtained.
[0057]
(Comparative Example 4)
In Example 7, polymerization was performed in the same manner as in Example 7 except that the first step was performed until the increase in the molecular weight of the polylactic acid composition was saturated, and the second step was not performed. The characteristics of the obtained polymerization product are as shown in Table 3, and the amount of residual lactide was very large at 3.5%.
[0058]
(Comparative Example 5)
In place of Al (Acac) 3 in Example 7, polymerization was carried out in the same manner as in Example 7 except that 0.1 mol% of Sn (Oct) 2 was used with respect to the lactide. The characteristics of the obtained polylactic acid composition are as shown in Table 3. The residual lactide amount was as very high as 1.8%, and the thermal stability was as low as 21%.
[0059]
[Table 3]
(Examples 9 and 10)
Polymerization was carried out in the same manner as in Example 7 except that the first step in Example 7 was changed until the residual lactide was 28.3% and 6.4%. The characteristics of the obtained polymerization product are as shown in Table 4. In any case, a polylactic acid composition having a high degree of polymerization and a low residual lactide amount was obtained in a high yield.
[0061]
(Comparative Example 6)
Polymerization was carried out in the same manner as in Example 7 except that the first step in Example 7 was changed to a residual lactide amount of 39.1%. The characteristics of the obtained polymerization product are as shown in Table 4. Since the amount of residual lactide after the first step was large, a polymerization product having a high degree of polymerization and a low residual lactide amount was obtained. Was as low as 55.2%.
[0062]
(Comparative Example 7)
Polymerization was carried out in the same manner as in Example 7 except that the first step in Example 7 was changed to a residual lactide amount of 4.3%. The characteristics of the obtained polymerization product are as shown in Table 4. Since the amount of residual lactide after the first step was too small, the lactide was not sufficiently removed in the second step, and the amount of residual lactide was 2 It became 3% [0063]
[Table 4]
【The invention's effect】
Since the polylactic acid composition obtained by the production method of the present invention has high thermal stability, the molecular weight during the molding process is maintained at 200,000 or more, and a high-strength molded product is obtained. In addition, the method of the present invention does not require post-treatment after lactide melt ring-opening polymerization, and a polylactic acid composition having a high molecular weight and excellent thermal stability can be obtained. . In addition, since a safer aluminum compound is used as a catalyst instead of the conventional tin compound, the safety is high even when used in biomaterials or food. Further, since the polylactic acid composition of the present invention has a small amount of residual lactide, the lactide does not volatilize during molding and does not contaminate the surrounding environment. The formation of voids derived from the residual lactide in the molded product and the low strength resulting therefrom A molded product having no part can be obtained. In addition, the method of the present invention does not use a method that requires a solvent removal step such as reprecipitation or washing for the removal of residual lactide in polylactic acid, and has a very high industrial value because the time required for polymerization is short. Furthermore, since the molded article of the present invention has high strength, powders and fibers used for clothing, daily life, pharmaceutical materials, medical materials, and industrial materials such as agriculture, fishery, industry, construction, civil engineering, etc. , Very suitable as a film and molding material.
Claims (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11016897A JP3752776B2 (en) | 1996-10-18 | 1997-04-10 | POLYLACTIC ACID COMPOSITION, PROCESS FOR PRODUCING THE SAME, AND MOLDED ARTICLE OF THE COMPOSITION |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8-297507 | 1996-10-18 | ||
| JP29750796 | 1996-10-18 | ||
| JP11016897A JP3752776B2 (en) | 1996-10-18 | 1997-04-10 | POLYLACTIC ACID COMPOSITION, PROCESS FOR PRODUCING THE SAME, AND MOLDED ARTICLE OF THE COMPOSITION |
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| Publication Number | Publication Date |
|---|---|
| JPH10176038A JPH10176038A (en) | 1998-06-30 |
| JP3752776B2 true JP3752776B2 (en) | 2006-03-08 |
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| US8362158B2 (en) | 2005-12-02 | 2013-01-29 | Kureha Corporation | Polyglycolic acid resin composition |
| JP6423654B2 (en) * | 2014-09-02 | 2018-11-14 | ネーチャーワークス エルエルシー | Polylactic acid resin for pulverized toner, polylactic acid resin composition for pulverized toner, and pulverized toner using the same |
| CN108384210B (en) * | 2018-04-04 | 2020-07-28 | 中国科学院长春应用化学研究所 | Application of pyruvate and modified polylactic acid |
| CN113583408A (en) * | 2021-08-04 | 2021-11-02 | 杨桂生 | High-performance full-biodegradable polylactic acid and preparation method thereof |
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