JP3845713B2 - Polylactic acid molded body - Google Patents
Polylactic acid molded body Download PDFInfo
- Publication number
- JP3845713B2 JP3845713B2 JP2002153954A JP2002153954A JP3845713B2 JP 3845713 B2 JP3845713 B2 JP 3845713B2 JP 2002153954 A JP2002153954 A JP 2002153954A JP 2002153954 A JP2002153954 A JP 2002153954A JP 3845713 B2 JP3845713 B2 JP 3845713B2
- Authority
- JP
- Japan
- Prior art keywords
- polylactic acid
- film
- molded body
- peo
- acid
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Description
【０００１】
【発明の属する技術分野】
本発明は、傾斜構造を有するポリ乳酸成形体に関するものである。
【０００２】
【従来の技術】
近年、天然資源の枯渇、環境保護の観点から大量生産・大量消費型の経済活動は見直され、循環型社会への移行を迫られている。プラスチックでは、再生産のできない化石燃料の消費や使用後の処理が問題となっている。埋め立て処分では処分場の不足や、埋め立てた廃棄物から染み出す有害物質による環境汚染、焼却処分の場合には燃焼温度が高すぎるために焼却炉を傷めたり、ダイオキシンなどの有害物質発生による環境汚染などがある。
【０００３】
これらの問題を解決する方策として、生分解性プラスチックの開発、利用が重要視されてきており、最近、価格が低下したこともあって、種々の分野で利用され始めている。現状、生分解性プラスチックの利用はプラスチック市場全体の1％にも満たないが、2017年には10％に達するとの試算もある。
【０００４】
生分解性プラスチックのなかでも農産廃棄物を原料として得られるポリ乳酸は、再生可能な資源から生まれるプラスチックであり、機械的特性、価格の面からも最も普及が期待されている。また環境面では生分解することから、廃棄物問題が生じない。
【０００５】
しかしながら、自然環境中であまりに容易に分解するようでは、日常の使用に支障を来す。通常、プラスチックに要求される強度と生分解性は相反するものであり両立は難しい。生分解性プラスチックも自然環境での分解にはある程度の時間を必要とするため、分解を促進する必要がある。特にポリ乳酸は、ガラス転移温度以上の環境（例えばコンポスト）では分解は速いが、外気温度（土中埋設など）では分解に数年を要する。
【０００６】
これまでに、ポリ乳酸の分解性を向上するためにポリ乳酸以外の成分とのブレンド法が検討されてきた。例えば、ポリエチレングリコール（J. Appl. Polym. Sci.、1997、66、1495）やクエン酸エステル（J. Appl. Polym. Sci.、1997、66、1507）、ポリビニルアルコール（J. Appl. Polym. Sci.、2001、 81、2151）、ポリカプロラクトン（J. Appl. Polym. Sci.、1998、67、405）、プルロニック（ポリアルキレンオキサイド共重合体）（Macromolecules、1992、25、116）、ゼラチン（J. Biomater. Sci. Polym. Ed.、1995、7、23）などに関する報告がある。
【０００７】
【発明が解決しようとする課題】
しかしながら、ポリ乳酸と異成分を均一にブレンドする方法ではポリ乳酸本来の強度を保つことが難しく、実用化の際の課題となっていた。
本発明は、ポリ乳酸本来の強度を保ったまま、環境中での生分解が容易であるようなポリ乳酸成形体を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明者らは、上記課題を解決するために鋭意検討した結果、ポリ乳酸とポリ乳酸以外の他の成分により傾斜構造を形成する成形体とすることにより、ポリ乳酸本来の強度を保ったまま、分解を促進させることが可能となることを見出し、本発明に到達した。
【０００９】
すなわち本発明は、ポリ乳酸とポリ乳酸以外の成分である以下の(ａ)〜（ｅ）からなる群より選ばれる1又は２以上の物質との傾斜構造を有する成形体であって、環境中で生分解性を有することを特徴とするポリ乳酸成形体を要旨とするものである。
(ａ)水溶性物質、（ｂ）生分解性物質、（ｃ）非水溶性無機物質（ただし、チタニアファイバーを除く）、（ｄ）可塑剤、（ｅ）界面活性剤
【００１０】
【発明の実施の態様】
以下、本発明を詳細に説明する。
本発明における傾斜構造とは、ポリ乳酸とポリ乳酸以外の他の成分（以下、本明細書において異成分という。）との混合物から得られる成形体に関して、ある方向にそって、ポリ乳酸と異成分の混合比率が連続的または断続的に変化している構造を指す。
本発明の傾斜構造を有するポリ乳酸成形体は、ポリ乳酸含有率の高い部分を有しているため、この部分がポリ乳酸本来の強度を維持することができる。従来のポリ乳酸と異成分とが均一に混合された成形体では、ポリ乳酸含有率の高い部分は存在せず、ポリ乳酸の強度を維持することが困難であった。したがって、均一混合された成形体と全体としてポリ乳酸含有率が等しい場合には、本発明の傾斜構造材料の方が強度が高くなることになる。
【００１１】
本発明のポリ乳酸成形体において、成形体全体が傾斜構造となっていてもよく、また成形体の一部分が傾斜構造となっていても構わない。傾斜構造を形成している部分におけるポリ乳酸および異成分の含有率に特に制限はなく、０％を超え、１００％未満であれば可能である。しかしながら、ポリ乳酸の強度特性を保つためにはポリ乳酸の含有量が３０％以上の部分が成形体の一部分において存在していることが好ましく、さらに好ましくは５０％以上である。
【００１２】
本発明における異成分としては、有機物および／または無機物であり、ポリ乳酸とともに成形体が得られ、ポリ乳酸の分解を阻害しない物質であれば何でも良い。異成分は１種類であっても2種類以上であってもよく、また、２種類以上の混合物であってもよい。さらに、異成分がポリ乳酸を含む混合物や共重合体であっても構わない。
【００１３】
異成分が有機物の場合、水溶性物質または生分解性物質が好ましい。
水溶性物質は、ポリ乳酸成形体を廃棄した際、水分に接触すると溶けだし、成形体中に微細な穴を形成し、ポリ乳酸の表面積を増大する。また水溶性物質が水分を吸着し、ポリ乳酸と水分との接触を促進する効果もある。これらの効果によってポリ乳酸の分解が促進されていると考えられる。
【００１４】
そのような水溶性物質としては、天然あるいは変性の多糖類、オリゴ糖類または単糖類、合成高分子、タンパク質などがあげられる。具体的には、メチルセルロース、エチルセルロース、ヒドロキシエチルセルロース、カルボキシメチルセルロース、酢酸セルロース、寒天、ゼラチン、プルラン、デキストラン、ポリエチレンオキサイド、ポリプロピレンオキサイド、ポリイソプロピルアルコール、ポリメタクリル酸、ポリアクリル酸、ポリビニルピロリドン、ポリビニルアルコール、ポリエチレンイミン、ポリアリルアミン、ポリアミン、アミノエチル化ポリマー、カチオン化デンプン、ポリビニルアミン、カチオン化ポリアクリルアミドなどがあげられる。また、これらの共重合体、化学修飾体であってもよい。これらのうち、ポリ乳酸との相溶性の点でポリエチレンオキサイドが好ましい。しかしながら、これらに限定されるものではなく、ポリ乳酸の分解を大きく阻害しないものであれば何でも用いることができる。
【００１５】
ここで用いられるポリエチレンオキサイドの数平均分子量は、水溶性の点で１０万以下が好ましく、さらに好ましくは１万以下である。
【００１６】
異成分として用いられる生分解性物質は、ポリ乳酸成形体を廃棄した際、水分や細菌の存在する土壌などに接触することで分解し、成形体中に微細な穴を形成し、ポリ乳酸の表面積を増大する。また生分解性物質が水分を吸着し、ポリ乳酸と水分との接触を促進する効果もある。これらの効果によってポリ乳酸の分解が促進されていると考えられる。
【００１７】
そのような生分解性物質としては、天然あるいは変性の多糖類、オリゴ糖類または単糖類、天然高分子、微生物産生高分子、合成高分子、タンパク質などが考えられる。具体的にはセルロース、ヒドロキシエチルセルロース、メチルセルロース、エチルセルロース、酢酸セルロース、ポリビニルアルコール、ポリエーテルウレタン変性物、キサンタンガム、寒天、ゼラチン、カラギーナン、カードラン、アルブミン、カゼイン、アルギン酸、アルギン酸エステル、ヒアルロン酸、コラーゲン、デンプン、天然ゴム、アラビナン、キチン、キトサン、シルクフィブロイン、グアーガム、ローカストビーンガム、グリコーゲン、グルコマンナン、マンナン、デキストラン、プルラン、ポリグリコール酸、ポリカプロラクトン、ポリエチレンサクシネート、ポリテトラメチレンサクシネート、ポリエステルカーボネート、ポリヒドロキシブチレート、ポリヒドロキシバリレート、ポリブチレンテレフタレート／アジペートなどがあげられる。また、これらの共重合体、化学修飾体であってもよい。しかしながら、これらに限定されるものではなく、ポリ乳酸の分解を大きく阻害しないものであれば何でも用いることができる。
【００１８】
本発明において異成分として無機物質でもよい。無機物質はポリ乳酸成形体を廃棄した際、水分に接触すると溶けだし、成形体中に微細な穴を形成し、ポリ乳酸の表面積を増大する。または、水分を吸着しポリ乳酸と水分との接触を促進したり、土壌中の分解細菌の生育を促進したりすると考えられる。これらの効果によってポリ乳酸の分解が促進されていると考えられる。
【００１９】
そのような無機物質としては、熱安定剤、安定化助剤、可塑剤、酸化防止剤、光安定剤、造核剤、重金属不活性化剤、難燃剤、滑剤、帯電防止剤、肥料、着色料、増粘剤などが考えられる。具体的には、硫酸アンモニウムや硝酸アンモニウム、硫酸ナトリウム、硝酸ナトリウム、塩化カリウム、塩化ナトリウム、石灰窒素、炭酸カルシウム、炭酸水素カルシウム、尿素、水酸化アルミニウム、塩化マグネシウム、水酸化マグネシウム、スルファミン酸グアニジン、リン酸グアニジン、トリエチルフォスフェート、重合性リン化合物、ポリリン酸などの水溶性物質が好ましい。しかしながら、これらに限定されるものではなく、ポリ乳酸の分解を大きく阻害しないものであれば何でも用いることができる。
【００２０】
また、本発明における異成分として、非水溶性物質を界面活性剤と混合して用いたり、水溶性または生分解性物質と混合したりして用いると、ポリ乳酸成形体より脱離し易くなり、脱離した際、微細な穴を形成してポリ乳酸の分解を促進する。
【００２１】
そのような非水溶性物質としては、熱安定剤、安定化助剤、可塑剤、酸化防止剤、光安定剤、造核剤、重金属不活性化剤、難燃剤、滑剤、帯電防止剤、肥料、着色料、増粘剤などが考えられる。具体的には、タルクや層状ケイ酸塩、ハイドロタルサイト、ゼオライト、カーボンブラック、シリカ、アルミナ、ハイドロキシアパタイト、シリコーン、炭酸カルシウム、モリブデン、ジルコニウム、酸化スズ、五酸化リン、三酸化アンチモン、ホウ酸亜鉛、クレーなどがあげられる。しかしながら、これらに限定されるものではなく、ポリ乳酸の分解を大きく阻害しないものであれば何でも用いることができる。
【００２２】
本発明における異成分として、可塑剤や界面活性剤を用いることもできる。可塑剤や界面活性剤はポリ乳酸成形体を廃棄した際、水分に接触すると溶けだし、成形体中に微細な穴を形成し、ポリ乳酸の表面積を増大する。または水分を吸着し、ポリ乳酸と水分との接触を促進する効果もある。これらの効果によってポリ乳酸の分解が促進していると考えられる。
【００２３】
そのような可塑剤としては、ポリアルキレンオキサイド、ポリアルキレンオキサイド共重合体、ポリアルキレンオキサイドトリオール、クエン酸誘導体、ソルビトール、マンニトール、ペンタエルスリトールエステル、グリセリンエステル、硬化ひまし油、エポキシ化植物油、ポリエステルオリゴマー、リン酸エステル、二塩基酸（セバシン酸、アゼライン酸、アジピン酸、フタル酸など）エステル、トリメリット酸エステル、エポキシ系オリゴマーなどがあげられる。しかしながら、これらに限定されるものではなく、ポリ乳酸の分解を大きく阻害しないものであれば何でも用いることができる。
【００２４】
また界面活性剤としては、リン酸エステル、石鹸（脂肪酸塩）、高級アルコールのポリオキシエチレンエーテル、硫酸化エステル塩、脂肪族アミンまたはアミドの硫酸塩、脂肪族アミンおよびアミドの塩類、アルキルエーテル類、アルキルエステル類、オキシエチレンソルビタン脂肪酸エステル、グリセリン脂肪酸エステル、ポリオキシエチレン、ポリオキシエチレン脂肪酸エステル、ポリオキシプロピレン、ポリアルキレンオキサイド共重合体、ポリエーテル変性シリコーンなどがあげられる。しかしながら、これらに限定されるものではなく、ポリ乳酸の分解を大きく阻害しないものであれば何でも用いることができる。
【００２５】
本発明のポリ乳酸成形体においては、ポリ乳酸および上記した異成分の他に、ポリ乳酸自身の特性を改良するために可塑剤を加えたり、ポリ乳酸と異成分との親和性を向上させるために界面活性剤などを含有してよい。
【００２６】
本発明のポリ乳酸成形体の形態としては、繊維、フィルム、スパンボンドなど様々な形態に加工されていてもよい。
【００２７】
次に、本発明のポリ乳酸成形体の作製方法について説明する。
本発明のポリ乳酸成形体を作製するには、溶液拡散法や積層法を採用することができる。しかしながら、これらに限定されるものではない。
溶液拡散法は、予め作製したポリ乳酸成形体表面に異成分を溶解した溶液を接触させ、ポリ乳酸と異成分とを混合させることにより表面に対して垂直方向に傾斜構造を形成させる方法である。したがって、ここで用いられる溶媒は、ポリ乳酸を溶解または膨潤する性質を有している必要がある。また、表面の一部に異成分の溶液を接触させた場合には表面に対し、平行な方向にも傾斜構造を形成することができる。また、ポリ乳酸と異成分との均一混合でできた成形体表面にポリ乳酸溶液を接触させ、同様の操作を行ってもよいし、接触させる溶液がポリ乳酸と異成分との混合物でもよい。
【００２８】
積層法は、ポリ乳酸と異成分の混合比率の異なる成形体を作製し、それらを重ね合わせることで傾斜構造を得る方法である。
【００２９】
本発明の傾斜構造を有するポリ乳酸成形体は、例えば包装容器に用いた場合、外気に接触する部分はポリ乳酸成分の多い構造とし、内部を異成分の多い構造とする。そうして使用後、廃棄する際に内部を外部環境にさらすと迅速な分解が始まる。また、ポリ乳酸成形体の傾斜構造をコントロールすることで分解速度を制御することも可能となる。
【００３０】
【実施例】
以下、実施例により本発明を具体的に説明する。
なお、実施例中の各種の分析方法は以下の通りである。
【００３１】
（１）分子量の測定
ポリ乳酸の分子量はGPC法によって測定した。GPC装置として、東ソー社製8020システムを用いた。カラムは東ソー社製のKF803L×1、KF806F×2を用い、THFを溶媒として流速1ml/minで測定を行った。ポリスチレンを分子量標準試料として用いた。
【００３２】
（２）顕微ラマン分光法による厚み方向のブレンド組成割合の測定
傾斜構造材料の厚み方向の成分濃度変化を調べるため、試料を切断し、断面を顕微ラマン分光分析器（RENISHAW社製、RAMASCOPE JRS-SYSTEM-1000）を用いて、小さなスポット領域（Φ2μm）を測定、評価した。成分比はラマンスペクトルで得られる各成分固有のピークを比較することで行った。例えば、ポリ乳酸ピークは873cm-1、PEOは844cm-1である。
【００３３】
（３）引っ張り試験
傾斜構造を有する成形体を10mm×30mmの短冊状に切断し、試料とし、オートグラフ（島津製作所製DSS-5000）を用いて引っ張り試験を行った。引っ張り試験はチャック間距離10mm、引っ張り速度5mm/minであった。測定はそれぞれ3回行い、その平均値を測定結果とした。
【００３４】
（４）酵素による分解実験
酵素溶液はpH7に調整した0.02％のアジ化ナトリウムを含有する10mMリン酸カリウム緩衝溶液にプロテイナーゼK（フナコシ（株）より購入）を5mg/mlだけ加えて調整した。さらに実験に用いた酵素分解実験溶液は酵素溶液2に対し、蒸留水42.5、2％アジ化ナトリウム水溶液0.5、リン酸カリウム緩衝溶液（0.5M、pH7）5の割合で混合することにより調整した。酵素分解実験溶液10mlに100mgのポリ乳酸フィルムを浸漬し、その重量減少および、形状変化を観察した。反応は振盪培養器中、27℃で振盪しながら行った。
【００３５】
ただし、重量減少は、ポリ乳酸成分の重量減少率を以下の方法によって算出した。酵素のない溶液を用いて同じフィルムの分解実験を行い、この重量減少量はポリ乳酸以外の成分の重量減少分であるとしてフィルム全体の重量減少量から除いた。この値をポリ乳酸の重量減少分として、はじめのポリ乳酸量（1g）に対する重量減少率を計算した。
【００３６】
（５）土中分解実験
フィルム状の成形体を用いて土中分解実験を行った。10cm×10cmの各種傾斜構造を有する（または有さない）試料を屋外の土壌の地下5cmに埋設し、重量変化および形態変化を観察した。観察期間は５ヶ月間で、平均気温は25℃、降雨量は750mmであった。
ただし、回収した試料を秤量してGPC測定を行い、実験前のポリ乳酸ピークの減少量をポリ乳酸成分の重量減少率として算出した。
【００３７】
実施例1〔溶液拡散法による傾斜構造材料の作製〕
ポリ乳酸（カーギル・ダウ社製、平均分子量210,000）1gにクロロホルム40mlを加えて溶解させた後、シャーレにキャストし、室温で溶媒を留去することによりポリ乳酸フィルムを得た。次ぎに、ポリエチレンオキサイド（PEO）（ポリエチレングリコール4000、平均分子量3,000、和光純薬工業より購入）0.6gをクロロホルムに溶解し、溶液をシャーレ中のポリ乳酸フィルム上にキャストした。さらに、クロロホルムの量を60mlおよび80mlとすることで異なる傾斜構造を有する3種類の試料を調整した。得られたフィルムはラマン分光法により、傾斜組成を確認した後（図１）、引っ張り試験（図３、表１）、酵素分解試験（図４、表１）、土中分解試験（図５、表１）を行った。結果はそれぞれ図表に示した。
【００３８】
実施例2〔積層法による傾斜構造材料の作製〕
ポリ乳酸0.2gおよびPEO0.32gにクロロホルム40mlを加えて溶解させた後、シャーレにキャストし、室温で溶媒を留去することによりポリ乳酸ブレンドフィルムを得た。さらにポリ乳酸は0.2gのまま、PEOをそれぞれ0.16g、0.08g、0.04g、0gとして同様にブレンドフィルムを作製した。これらのフィルムをPEOの組成比の順に重ね合わせて、170℃、5秒間、熱プレスした。すぐに冷却し、傾斜構造を有するフィルムを得た。得られたフィルムは、引っ張り試験（図３、表１）、酵素分解試験（図４、表１）、土中分解試験（図５、表１）を行った。結果はそれぞれ図表に示した。
【００３９】
実施例3〔積層法による傾斜構造材料の作製〕
ポリ乳酸0.33gおよびPEO0.4gにクロロホルム40mlを加えて溶解させた後、シャーレにキャストし、室温で溶媒を留去することによりポリ乳酸ブレンドフィルムを得た。さらにポリ乳酸は0.33gのまま、PEOをそれぞれ0.2g、0gとして同様にブレンドフィルムを作製した。これらのフィルムをPEOの組成比の順に重ね合わせて170℃、5秒間、熱プレスした。すぐに冷却し、傾斜構造を有するフィルムを得た。得られたフィルムは、引っ張り試験（図３、表１）、酵素分解試験（図４、表１）、土中分解試験（図５、表１）を行った。結果はそれぞれ図表に示した。
【００４０】
比較例1〔ポリ乳酸フィルムの作製〕
ポリ乳酸1.6gにクロロホルム40mlを加えて溶解させた後、シャーレにキャストし、室温で溶媒を留去することによりポリ乳酸フィルムを得た。得られたフィルムは、引っ張り試験（図３、表１）、酵素分解試験（図４、表１）、土中分解試験（図５、表１）を行った。結果はそれぞれ図表に示した。
【００４１】
比較例２〔均一ブレンド材料の作製〕
ポリ乳酸1gおよびPEO0.6gにクロロホルム40mlを加えて溶解させた後、シャーレにキャストし、室温で溶媒を留去することによりポリ乳酸-PEO均一ブレンドフィルムを得た。得られたフィルムは、引っ張り試験（図３、表１）、酵素分解試験（図４、表１）、土中分解試験（図５、表１）を行った。結果はそれぞれ図表に示した。
【００４２】
比較例３〔二層構造材料の作製〕
ポリ乳酸1gにクロロホルム40mlを加えて溶解させた後、シャーレにキャストし、室温で溶媒を留去することによりポリ乳酸フィルムを得た。次ぎに、PEO0.6gをメタノール50mlに溶解し、溶液をシャーレ中のポリ乳酸フィルム上にキャストした。室温でメタノールを留去し、二層構造を有するフィルムを得た。得られたフィルムは、引っ張り試験（図３、表１）、酵素分解試験（図４、表１）、土中分解試験（図５、表１）を行った。結果はそれぞれ図表に示した。
【００４３】
実施例４〔溶液拡散法による傾斜構造材料の作製〕
PEOの代わりにビオノーレ（ビオノーレ＃1010、平均分子量80,000、昭和高分子社製）を用いた以外は実施例１と同様に傾斜構造フィルムを作製した。ただし作製したフィルムは1種類のみである。得られたフィルムはラマン分光法により、傾斜組成を確認した後（図２）、引っ張り試験、酵素分解試験、土中分解試験を行った。結果を表1に示した。
【００４４】
比較例４〔均一ブレンドフィルムの作製〕
PEOの代わりにビオノーレを用いた以外は比較例２と同様に均一ブレンドフィルムを作製した。得られたフィルムは、引っ張り試験、酵素分解試験、土中分解試験を行った。結果をそれぞれ表1に示した。
【００４５】
実施例５〔溶液拡散法による傾斜構造材料の作製〕
PEOの代わりにBis(butyldiglycol)adipate（BXA）（大八化学社製）0.3gを用いた以外は実施例1と同様に傾斜構造フィルムを作製した。ただし作製したフィルムは1種類のみである。得られたフィルムはラマン分光法により、傾斜組成を確認した後（図２）、引っ張り試験、酵素分解試験、土中分解試験を行った。結果を表1に示した。
【００４６】
比較例５〔均一ブレンドフィルムの作製〕
PEOの代わりにBXA0.3gを用いた以外は比較例２と同様に均一ブレンドフィルムを作製した。得られたフィルムは、引っ張り試験、酵素分解試験、土中分解試験を行った。結果を表1に示した。
【００４７】
実施例６〔積層法による傾斜構造材料の作製〕
PEOの代わりに硫酸ナトリウム（和光純薬工業より購入）を用いた以外は実施例２と同様にキャストフィルムを作製した。作製したフィルムは硫酸ナトリウムの組成比の順に重ね合わせ、170℃で5秒間、熱プレスした後、急冷し、傾斜構造フィルムを得た。得られたフィルムは、引っ張り試験、酵素分解試験、土中分解試験を行った。結果を表1に示した。
【００４８】
比較例６〔均一ブレンドフィルムの作製〕
PEOの代わりに硫酸ナトリウムを用いた以外は比較例２と同様に均一ブレンドフィルムを作製した。得られたフィルムは、引っ張り試験、酵素分解試験、土中分解試験を行った。結果を表1に示した。
【００４９】
実施例７〔積層法による傾斜構造材料の作製〕
PEOの代わりにタルク（MICEL-TONE、平均粒径1.4μm、林化成社製）およびPEOを用いた以外は実施例2と同様にキャストフィルムを作製した。タルクとPEOの割合は1：1であった。作製したフィルムはタルクとPEO混合物の組成比の順に重ね合わせ、170℃で5秒間、熱プレスした後、急冷し、傾斜構造フィルムを得た。得られたフィルムは、引っ張り試験、酵素分解試験、土中分解試験を行った。結果をそれぞれ表1に示した。
【００５０】
比較例７〔均一ブレンドフィルムの作製〕
PEOの代わりにタルクとPEO混合物を用いた以外は比較例２と同様に均一ブレンドフィルムを作製した。得られたフィルムは、引っ張り試験、酵素分解試験、土中分解試験を行った。結果を表1に示した。
【００５１】
実施例８〔積層法による傾斜構造材料の作製〕
PEOの代わりにポリビニルアルコール（PVA）（ポリビニルアルコール、平均重合度2,000、和光純薬工業より購入）、クロロホルムの代わりにヘキサフルオロイソプロパノールを用いた以外は実施例２と同様にキャストフィルムを作製した。作製したフィルムはPVAの組成比の順に重ね合わせ、170℃で5秒間、熱プレスした後、急冷し、傾斜構造フィルムを得た。得られたフィルムは、引っ張り試験、酵素分解試験、土中分解試験を行った。結果を表1に示した。
【００５２】
比較例８〔均一ブレンドフィルムの作製〕
PEOの代わりにPVAを用いた以外は比較例２と同様に均一ブレンドフィルムを作製した。得られたフィルムは、引っ張り試験、酵素分解試験、土中分解試験を行った。結果を表1に示した。
【００５３】
【表１】
図１の結果から、溶液拡散法によって傾斜構造材料が得られたことが確認できた。図３および表１の結果を見ると、傾斜構造材料を有するフィルムの強度はポリ乳酸フィルムや二層構造フィルムに比較しても同等の強度を保持していることがわかる。均一ブレンドフィルムでは強度の低下が顕著である。
【００５５】
図４、図５および表１からは傾斜構造材料におけるポリ乳酸成分の分解が均一ブレンドフィルムに比べても非常に速いことがわかる。二層構造材料およびポリ乳酸フィルムではポリ乳酸の分解は非常に遅い。
【００５６】
以上の結果から、傾斜構造を有するポリ乳酸成形体はポリ乳酸の強度は保ったまま、他の構造のポリ乳酸成形体に比べて分解速度が著しく速くなることがわかった。したがって、本発明のポリ乳酸成形体は、ポリ乳酸成型品の強度は保ったまま、分解性を向上することが可能となった。
【００５７】
【発明の効果】
本発明によれば、ポリ乳酸成形体の強度を保ったまま、分解性を向上させることが可能となった。
【図面の簡単な説明】
【図１】実施例１で得られたフィルムについて、ラマン分光法によるフィルム厚み方向に対するポリ乳酸比率を示した図である。
【図２】実施例４および５で得られたフィルムについて、ラマン分光法によるフィルム厚み方向に対するポリ乳酸比率を示した図である。
【図３】実施例１〜３、比較例１〜３で得られたフィルムについて引っ張り強度を示した図である。
【図４】実施例１〜３、比較例１〜３で得られたフィルムについて酵素による分解結果を示した図である。
【図５】実施例１〜３、比較例１〜３で得られたフィルムについて土中での分解結果を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polylactic acid molded article having an inclined structure.
[0002]
[Prior art]
In recent years, from the viewpoints of depletion of natural resources and environmental protection, mass-production / mass-consumption economic activities have been reviewed, and it has been forced to shift to a recycling-oriented society. For plastics, consumption of fossil fuels that cannot be reproduced and processing after use are problematic. In the case of landfill disposal, there is a shortage of disposal sites, environmental pollution due to harmful substances exuding from the landfilled waste, and in the case of incineration, the combustion temperature is too high and the incinerator is damaged, and environmental pollution is caused by the generation of harmful substances such as dioxins. and so on.
[0003]
Development and utilization of biodegradable plastics have been regarded as important measures for solving these problems, and recently, they have begun to be used in various fields due to a decrease in price. At present, the use of biodegradable plastics is less than 1% of the total plastic market, but it is estimated that it will reach 10% in 2017.
[0004]
Among biodegradable plastics, polylactic acid obtained from agricultural wastes is a plastic produced from renewable resources, and is expected to be most popular in terms of mechanical properties and price. In addition, because it is biodegradable in terms of environment, there is no waste problem.
[0005]
However, if it decomposes too easily in the natural environment, it will interfere with daily use. Usually, the strength and biodegradability required for plastics are contradictory and difficult to achieve. Biodegradable plastics also require a certain amount of time to decompose in the natural environment, so it is necessary to accelerate the decomposition. In particular, polylactic acid decomposes rapidly in an environment above the glass transition temperature (for example, compost), but it takes several years to decompose at an outside air temperature (such as buried in the soil).
[0006]
So far, blending methods with components other than polylactic acid have been studied in order to improve the degradability of polylactic acid. For example, polyethylene glycol (J. Appl. Polym. Sci., 1997, 66, 1495), citric acid ester (J. Appl. Polym. Sci., 1997, 66, 1507), polyvinyl alcohol (J. Appl. Polym. Sci., 2001, 81, 2151), polycaprolactone (J. Appl. Polym. Sci., 1998, 67, 405), pluronic (polyalkylene oxide copolymer) (Macromolecules, 1992, 25, 116), gelatin ( J. Biomater. Sci. Polym. Ed., 1995, 7, 23).
[0007]
[Problems to be solved by the invention]
However, it is difficult to maintain the original strength of polylactic acid by the method of uniformly blending polylactic acid and different components, which has been a problem in practical use.
An object of the present invention is to provide a polylactic acid molded article that can be easily biodegraded in the environment while maintaining the original strength of polylactic acid.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have made a molded body that forms an inclined structure with polylactic acid and other components other than polylactic acid, while maintaining the original strength of polylactic acid. The present inventors have found that it is possible to promote decomposition and have reached the present invention.
[0009]
That is, the present invention is a molded article having an inclined structure with polylactic acid and one or more substances selected from the group consisting of the following (a) to (e) which are components other than polylactic acid, And a polylactic acid molded article characterized by having biodegradability.
(a) water-soluble substance, (b) biodegradable substance, (c) water-insoluble inorganic substance (except for titania fiber), (d) plasticizer, (e) surfactant
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
In the present invention, the inclined structure refers to a molded body obtained from a mixture of polylactic acid and other components other than polylactic acid (hereinafter referred to as different components in the present specification), and is different from polylactic acid in a certain direction. It refers to a structure in which the mixing ratio of components changes continuously or intermittently.
Since the polylactic acid molded article having the inclined structure of the present invention has a portion having a high polylactic acid content, this portion can maintain the original strength of polylactic acid. In the conventional molded body in which the polylactic acid and the different component are uniformly mixed, there is no portion having a high polylactic acid content, and it is difficult to maintain the strength of the polylactic acid. Therefore, when the uniformly mixed shaped body and the polylactic acid content as a whole are equal, the gradient structure material of the present invention has higher strength.
[0011]
In the polylactic acid molded body of the present invention, the entire molded body may have an inclined structure, or a part of the molded body may have an inclined structure. There is no restriction | limiting in particular in the content rate of the polylactic acid and a different component in the part which forms the inclination structure, and if it exceeds 0% and less than 100%, it is possible. However, in order to maintain the strength characteristics of polylactic acid, it is preferable that a portion where the content of polylactic acid is 30% or more is present in a part of the molded body, and more preferably 50% or more.
[0012]
As the different component in the present invention, any substance may be used as long as it is an organic substance and / or an inorganic substance and a molded body is obtained together with polylactic acid and does not inhibit the decomposition of polylactic acid. The different component may be one type or two or more types, or may be a mixture of two or more types. Furthermore, the different component may be a mixture or copolymer containing polylactic acid.
[0013]
When the foreign component is an organic substance, a water-soluble substance or a biodegradable substance is preferable.
When the polylactic acid molded product is discarded, the water-soluble substance starts to dissolve when it comes into contact with moisture, forming fine holes in the molded product, and increasing the surface area of the polylactic acid. The water-soluble substance also has an effect of adsorbing moisture and promoting contact between polylactic acid and moisture. It is considered that the degradation of polylactic acid is promoted by these effects.
[0014]
Examples of such water-soluble substances include natural or modified polysaccharides, oligosaccharides or monosaccharides, synthetic polymers, proteins, and the like. Specifically, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, cellulose acetate, agar, gelatin, pullulan, dextran, polyethylene oxide, polypropylene oxide, polyisopropyl alcohol, polymethacrylic acid, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl alcohol, Examples include polyethyleneimine, polyallylamine, polyamine, aminoethylated polymer, cationized starch, polyvinylamine, and cationized polyacrylamide. Further, these copolymers and chemically modified products may be used. Among these, polyethylene oxide is preferable in terms of compatibility with polylactic acid. However, it is not limited to these, and anything that does not significantly inhibit the degradation of polylactic acid can be used.
[0015]
The number average molecular weight of the polyethylene oxide used here is preferably 100,000 or less, more preferably 10,000 or less, from the viewpoint of water solubility.
[0016]
Biodegradable substances used as different components are decomposed by contact with water or soil where bacteria are present when the polylactic acid molded product is discarded, forming fine holes in the molded product. Increase surface area. The biodegradable substance also has an effect of adsorbing moisture and promoting contact between polylactic acid and moisture. It is considered that the degradation of polylactic acid is promoted by these effects.
[0017]
Examples of such biodegradable substances include natural or modified polysaccharides, oligosaccharides or monosaccharides, natural polymers, microorganism-produced polymers, synthetic polymers, proteins, and the like. Specifically, cellulose, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, cellulose acetate, polyvinyl alcohol, polyether urethane modified product, xanthan gum, agar, gelatin, carrageenan, curdlan, albumin, casein, alginic acid, alginic acid ester, hyaluronic acid, collagen, Starch, natural rubber, arabinan, chitin, chitosan, silk fibroin, guar gum, locust bean gum, glycogen, glucomannan, mannan, dextran, pullulan, polyglycolic acid, polycaprolactone, polyethylene succinate, polytetramethylene succinate, polyester carbonate , Polyhydroxybutyrate, polyhydroxyvalylate, polybutylene terephthalate / adip Such as theft, and the like. Further, these copolymers and chemically modified products may be used. However, it is not limited to these, and anything that does not significantly inhibit the degradation of polylactic acid can be used.
[0018]
In the present invention, an inorganic substance may be used as the different component. When the polylactic acid molded body is discarded, the inorganic substance starts to dissolve when it comes into contact with moisture, forming fine holes in the molded body, and increasing the surface area of the polylactic acid. Alternatively, it is considered that moisture is adsorbed to promote contact between polylactic acid and moisture, or growth of degrading bacteria in soil is promoted. It is considered that the degradation of polylactic acid is promoted by these effects.
[0019]
Such inorganic substances include heat stabilizers, stabilization aids, plasticizers, antioxidants, light stabilizers, nucleating agents, heavy metal deactivators, flame retardants, lubricants, antistatic agents, fertilizers, coloring. A material, a thickener, etc. can be considered. Specifically, ammonium sulfate, ammonium nitrate, sodium sulfate, sodium nitrate, potassium chloride, sodium chloride, lime nitrogen, calcium carbonate, calcium bicarbonate, urea, aluminum hydroxide, magnesium chloride, magnesium hydroxide, guanidine sulfamate, phosphoric acid Water-soluble substances such as guanidine, triethyl phosphate, polymerizable phosphorus compounds and polyphosphoric acid are preferred. However, it is not limited to these, and anything that does not significantly inhibit the degradation of polylactic acid can be used.
[0020]
In addition, as a different component in the present invention, a water-insoluble substance is mixed with a surfactant, or when mixed with a water-soluble or biodegradable substance, the polylactic acid molded product is easily detached. When detached, a fine hole is formed to promote the decomposition of polylactic acid.
[0021]
Such water-insoluble substances include heat stabilizers, stabilization aids, plasticizers, antioxidants, light stabilizers, nucleating agents, heavy metal deactivators, flame retardants, lubricants, antistatic agents, fertilizers Coloring agents, thickeners, etc. are conceivable. Specifically, talc, layered silicate, hydrotalcite, zeolite, carbon black, silica, alumina, hydroxyapatite, silicone, calcium carbonate, molybdenum, zirconium, tin oxide, phosphorus pentoxide, antimony trioxide, boric acid Examples include zinc and clay. However, it is not limited to these, and anything that does not significantly inhibit the degradation of polylactic acid can be used.
[0022]
As the different component in the present invention, a plasticizer or a surfactant can also be used. When the polylactic acid molded body is discarded, the plasticizer and the surfactant start to dissolve when they come into contact with moisture, thereby forming fine holes in the molded body and increasing the surface area of the polylactic acid. Alternatively, it has an effect of adsorbing moisture and promoting contact between polylactic acid and moisture. It is considered that the degradation of polylactic acid is promoted by these effects.
[0023]
Such plasticizers include polyalkylene oxides, polyalkylene oxide copolymers, polyalkylene oxide triols, citric acid derivatives, sorbitol, mannitol, pentaerythritol esters, glycerin esters, hydrogenated castor oil, epoxidized vegetable oils, polyester oligomers. And phosphoric acid esters, dibasic acids (sebacic acid, azelaic acid, adipic acid, phthalic acid, etc.) esters, trimellitic acid esters, epoxy oligomers, and the like. However, it is not limited to these, and anything that does not significantly inhibit the degradation of polylactic acid can be used.
[0024]
Surfactants include phosphate esters, soaps (fatty acid salts), polyoxyethylene ethers of higher alcohols, sulfated ester salts, aliphatic amine or amide sulfates, aliphatic amine and amide salts, alkyl ethers. Alkyl esters, oxyethylene sorbitan fatty acid ester, glycerin fatty acid ester, polyoxyethylene, polyoxyethylene fatty acid ester, polyoxypropylene, polyalkylene oxide copolymer, polyether-modified silicone and the like. However, it is not limited to these, and anything that does not significantly inhibit the degradation of polylactic acid can be used.
[0025]
In the polylactic acid molded article of the present invention, in addition to polylactic acid and the above-mentioned different components, a plasticizer is added to improve the properties of polylactic acid itself, or the affinity between polylactic acid and the different components is improved. May contain a surfactant and the like.
[0026]
As a form of the polylactic acid molded body of the present invention, it may be processed into various forms such as a fiber, a film, and a spun bond.
[0027]
Next, a method for producing the polylactic acid molded body of the present invention will be described.
In order to produce the polylactic acid molded article of the present invention, a solution diffusion method or a lamination method can be employed. However, it is not limited to these.
The solution diffusion method is a method in which an inclined structure is formed in a direction perpendicular to the surface by bringing a solution in which a different component is dissolved into contact with the surface of a polylactic acid molded body prepared in advance and mixing the polylactic acid and the different component. . Therefore, the solvent used here needs to have a property of dissolving or swelling polylactic acid. Further, when a different component solution is brought into contact with a part of the surface, an inclined structure can be formed in a direction parallel to the surface. Further, the polylactic acid solution may be brought into contact with the surface of the molded body formed by uniformly mixing polylactic acid and the different component, and the same operation may be performed, or the solution to be contacted may be a mixture of polylactic acid and the different component.
[0028]
The lamination method is a method in which molded bodies having different mixing ratios of polylactic acid and different components are produced, and an inclined structure is obtained by superposing them.
[0029]
When the polylactic acid molded body having an inclined structure according to the present invention is used in, for example, a packaging container, the portion that comes into contact with the outside air has a structure with a large amount of polylactic acid components, and the inside has a structure with many different components. Thus, after use, when disposing of the interior, it will be quickly decomposed when exposed to the external environment. It is also possible to control the decomposition rate by controlling the inclined structure of the polylactic acid molded body.
[0030]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
In addition, the various analysis methods in an Example are as follows.
[0031]
(1) Measurement of molecular weight The molecular weight of polylactic acid was measured by GPC method. An 8020 system manufactured by Tosoh Corporation was used as the GPC apparatus. The columns were KF803L × 1 and KF806F × 2 manufactured by Tosoh Corporation, and measurement was performed at a flow rate of 1 ml / min using THF as a solvent. Polystyrene was used as a molecular weight standard sample.
[0032]
(2) Measurement of blend composition ratio in the thickness direction by micro-Raman spectroscopy In order to investigate the change in the component concentration in the thickness direction of the gradient structure material, the sample was cut and the cross-section was analyzed by a micro-Raman spectroanalyzer (manufactured by Renishiwa, RAMASCOPE JRS Using SYSTEM-1000), a small spot area (Φ2μm) was measured and evaluated. The component ratio was determined by comparing peaks specific to each component obtained by Raman spectra. For example, the polylactic acid peak is 873 cm −1 and the PEO is 844 cm −1 .
[0033]
(3) Tensile test A compact having an inclined structure was cut into a strip of 10 mm x 30 mm, used as a sample, and subjected to a tensile test using an autograph (DSS-5000 manufactured by Shimadzu Corporation). In the tensile test, the distance between chucks was 10 mm, and the tensile speed was 5 mm / min. Each measurement was performed three times, and the average value was taken as the measurement result.
[0034]
(4) Enzymatic degradation experiment The enzyme solution was prepared by adding 5 mg / ml of proteinase K (purchased from Funakoshi Co., Ltd.) to a 10 mM potassium phosphate buffer solution containing 0.02% sodium azide adjusted to pH 7. Furthermore, the enzyme decomposition experimental solution used in the experiment was prepared by mixing the
[0035]
However, the weight reduction was calculated by the following method for the weight reduction rate of the polylactic acid component. The same film degradation experiment was performed using a solution without an enzyme, and this weight loss amount was excluded from the weight loss amount of the entire film as being a weight loss amount of components other than polylactic acid. Using this value as the weight loss of polylactic acid, the weight reduction rate relative to the initial polylactic acid amount (1 g) was calculated.
[0036]
(5) Decomposition experiment in soil Decomposition experiment in soil was performed using a film-like molded product. Samples having (or not having) various inclined structures of 10 cm × 10 cm were embedded in 5 cm underground of outdoor soil, and changes in weight and morphology were observed. The observation period was 5 months, the average temperature was 25 ° C, and the rainfall was 750 mm.
However, the collected samples were weighed and subjected to GPC measurement, and the decrease amount of the polylactic acid peak before the experiment was calculated as the weight reduction rate of the polylactic acid component.
[0037]
Example 1 (Production of gradient structure material by solution diffusion method)
After adding 40 ml of chloroform to 1 g of polylactic acid (Cargill Dow, average molecular weight 210,000) and dissolving, cast into a petri dish, and the solvent was distilled off at room temperature to obtain a polylactic acid film. Next, 0.6 g of polyethylene oxide (PEO) (polyethylene glycol 4000, average molecular weight 3,000, purchased from Wako Pure Chemical Industries) was dissolved in chloroform, and the solution was cast on a polylactic acid film in a petri dish. Furthermore, three types of samples having different inclined structures were prepared by adjusting the amounts of chloroform to 60 ml and 80 ml. After confirming the gradient composition by Raman spectroscopy (FIG. 1), the obtained film was subjected to a tensile test (FIG. 3, Table 1), an enzymatic degradation test (FIG. 4, Table 1), a soil degradation test (FIG. 5, Table 1) was performed. The results are shown in the chart.
[0038]
Example 2 (Production of gradient structure material by lamination method)
After adding 40 ml of chloroform to 0.2 g of polylactic acid and 0.32 g of PEO and dissolving, it was cast in a petri dish and the solvent was distilled off at room temperature to obtain a polylactic acid blend film. Furthermore, blend films were prepared in the same manner with polylactic acid at 0.2 g and PEO at 0.16 g, 0.08 g, 0.04 g, and 0 g, respectively. These films were superposed in the order of the composition ratio of PEO, and hot-pressed at 170 ° C. for 5 seconds. The film was immediately cooled to obtain a film having an inclined structure. The obtained film was subjected to a tensile test (FIG. 3, Table 1), an enzymatic degradation test (FIG. 4, Table 1), and a soil degradation test (FIG. 5, Table 1). The results are shown in the chart.
[0039]
Example 3 (Production of gradient structure material by lamination method)
After adding 40 ml of chloroform to 0.33 g of polylactic acid and 0.4 g of PEO and dissolving, it was cast in a petri dish and the solvent was distilled off at room temperature to obtain a polylactic acid blend film. Further, a blend film was prepared in the same manner with the polylactic acid remaining at 0.33 g and the PEO at 0.2 g and 0 g, respectively. These films were superposed in the order of the composition ratio of PEO and hot-pressed at 170 ° C. for 5 seconds. The film was immediately cooled to obtain a film having an inclined structure. The obtained film was subjected to a tensile test (FIG. 3, Table 1), an enzymatic degradation test (FIG. 4, Table 1), and a soil degradation test (FIG. 5, Table 1). The results are shown in the chart.
[0040]
Comparative Example 1 (Production of polylactic acid film)
After adding 40 ml of chloroform to 1.6 g of polylactic acid and dissolving, it was cast into a petri dish and the solvent was distilled off at room temperature to obtain a polylactic acid film. The obtained film was subjected to a tensile test (FIG. 3, Table 1), an enzymatic degradation test (FIG. 4, Table 1), and a soil degradation test (FIG. 5, Table 1). The results are shown in the chart.
[0041]
Comparative Example 2 [Production of Uniform Blend Material]
After adding 40 ml of chloroform to 1 g of polylactic acid and 0.6 g of PEO and dissolving, it was cast into a petri dish and the solvent was distilled off at room temperature to obtain a polylactic acid-PEO uniform blend film. The obtained film was subjected to a tensile test (FIG. 3, Table 1), an enzymatic degradation test (FIG. 4, Table 1), and a soil degradation test (FIG. 5, Table 1). The results are shown in the chart.
[0042]
Comparative Example 3 [Production of two-layer structure material]
After adding 40 ml of chloroform to 1 g of polylactic acid and dissolving, it was cast in a petri dish and the solvent was distilled off at room temperature to obtain a polylactic acid film. Next, 0.6 g of PEO was dissolved in 50 ml of methanol, and the solution was cast on a polylactic acid film in a petri dish. Methanol was distilled off at room temperature to obtain a film having a two-layer structure. The obtained film was subjected to a tensile test (FIG. 3, Table 1), an enzymatic degradation test (FIG. 4, Table 1), and a soil degradation test (FIG. 5, Table 1). The results are shown in the chart.
[0043]
Example 4 [Production of gradient structure material by solution diffusion method]
A gradient structure film was produced in the same manner as in Example 1 except that Bionore (Bionore # 1010, average molecular weight 80,000, Showa Polymer Co., Ltd.) was used instead of PEO. However, only one type of film was produced. The obtained film was confirmed for the gradient composition by Raman spectroscopy (FIG. 2), and then subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1.
[0044]
Comparative Example 4 [Production of Uniform Blend Film]
A uniform blend film was prepared in the same manner as in Comparative Example 2 except that Bionore was used instead of PEO. The obtained film was subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1, respectively.
[0045]
Example 5 [Production of gradient structure material by solution diffusion method]
A gradient structure film was produced in the same manner as in Example 1 except that 0.3 g of Bis (butyldiglycol) adipate (BXA) (manufactured by Daihachi Chemical Co., Ltd.) was used instead of PEO. However, only one type of film was produced. The obtained film was confirmed for the gradient composition by Raman spectroscopy (FIG. 2), and then subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1.
[0046]
Comparative Example 5 [Preparation of Uniform Blend Film]
A uniform blend film was prepared in the same manner as in Comparative Example 2 except that 0.3 g of BXA was used instead of PEO. The obtained film was subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1.
[0047]
Example 6 [Production of Gradient Structure Material by Laminating Method]
A cast film was produced in the same manner as in Example 2 except that sodium sulfate (purchased from Wako Pure Chemical Industries) was used instead of PEO. The produced films were superposed in the order of the composition ratio of sodium sulfate, hot-pressed at 170 ° C. for 5 seconds, and then rapidly cooled to obtain an inclined structure film. The obtained film was subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1.
[0048]
Comparative Example 6 [Production of Uniform Blend Film]
A uniform blend film was prepared in the same manner as Comparative Example 2 except that sodium sulfate was used instead of PEO. The obtained film was subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1.
[0049]
Example 7 [Production of Gradient Structure Material by Lamination Method]
A cast film was produced in the same manner as in Example 2 except that talc (MICEL-TONE, average particle size 1.4 μm, Hayashi Kasei Co., Ltd.) and PEO were used instead of PEO. The ratio of talc to PEO was 1: 1. The produced film was superposed in the order of the composition ratio of talc and PEO mixture, hot-pressed at 170 ° C. for 5 seconds, and then rapidly cooled to obtain an inclined structure film. The obtained film was subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1, respectively.
[0050]
Comparative Example 7 (Preparation of uniform blend film)
A uniform blend film was prepared in the same manner as in Comparative Example 2 except that talc and PEO mixture were used instead of PEO. The obtained film was subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1.
[0051]
Example 8 [Production of gradient structure material by lamination method]
A cast film was prepared in the same manner as in Example 2 except that polyvinyl alcohol (PVA) (polyvinyl alcohol, average polymerization degree 2,000, purchased from Wako Pure Chemical Industries, Ltd.) was used instead of PEO, and hexafluoroisopropanol was used instead of chloroform. The produced films were superposed in the order of the composition ratio of PVA, hot-pressed at 170 ° C. for 5 seconds, and then rapidly cooled to obtain a gradient structure film. The obtained film was subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1.
[0052]
Comparative Example 8 [Production of Uniform Blend Film]
A uniform blend film was prepared in the same manner as in Comparative Example 2 except that PVA was used instead of PEO. The obtained film was subjected to a tensile test, an enzymatic degradation test, and a soil degradation test. The results are shown in Table 1.
[0053]
[Table 1]
From the result of FIG. 1, it was confirmed that the gradient structure material was obtained by the solution diffusion method. From the results shown in FIG. 3 and Table 1, it can be seen that the strength of the film having the gradient structure material maintains the same strength as compared with the polylactic acid film or the two-layer structure film. In the uniform blend film, the decrease in strength is remarkable.
[0055]
4 and 5 and Table 1 show that the degradation of the polylactic acid component in the gradient structure material is much faster than that of the uniform blend film. The degradation of polylactic acid is very slow in bilayer structure materials and polylactic acid films.
[0056]
From the above results, it was found that the degradation rate of the polylactic acid molded product having an inclined structure was remarkably increased as compared with the polylactic acid molded products having other structures while maintaining the strength of the polylactic acid. Therefore, the polylactic acid molded product of the present invention can be improved in degradability while maintaining the strength of the polylactic acid molded product.
[0057]
【The invention's effect】
According to the present invention, it is possible to improve the decomposability while maintaining the strength of the polylactic acid molded body.
[Brief description of the drawings]
1 is a graph showing the ratio of polylactic acid in the film thickness direction by Raman spectroscopy for the film obtained in Example 1. FIG.
FIG. 2 is a graph showing the polylactic acid ratio in the film thickness direction by Raman spectroscopy for the films obtained in Examples 4 and 5.
FIG. 3 is a diagram showing the tensile strength of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 3.
FIG. 4 is a diagram showing the results of enzymatic degradation of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 3.
FIG. 5 is a diagram showing the results of decomposition of the films obtained in Examples 1 to 3 and Comparative Examples 1 to 3 in soil.
Claims (1)
(ａ)水溶性物質、（ｂ）生分解性物質、（ｃ）非水溶性無機物質（ただし、チタニアファイバーを除く）、（ｄ）可塑剤、（ｅ）界面活性剤A molded body having an inclined structure with polylactic acid and one or more substances selected from the group consisting of the following (a) to (e) which are components other than polylactic acid, and biodegradable in the environment A polylactic acid molded article comprising:
(a) water-soluble substance, (b) biodegradable substance, (c) non-water-soluble inorganic substance (excluding titania fiber), (d) plasticizer, (e) surfactant
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