Fracture behavior of quenched poly(lactic acid)

機(jī)譯：淬火聚（乳酸）的斷裂行為

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摘要

The effect of a quenching treatment applied on heated cast sheet extruded films of two poly(lactic acid) (PLA)\udcommercial grades, with different optical purities, was studied. The thermal and mechanical properties of the films, as well\udas their fracture behavior, were assessed by differential scanning calorimetry (DSC), tensile tests, and the essential work of\udfracture (EWF) approach. The heating-quenching treatment causes a de-aging effect with an increase in the free volume of\udpolymer chains evidenced by a decrease in the glass transition temperature (Tg) and a decrease in the tensile stiffness and\udyield stress. As a result, there is an abrupt increase in ductility, finding a dramatic change in the fracture behavior, from brittle\udto ductile. The use of digital image correlation (DIC) of the strain field analysis during fracture testing has allowed relating\udthe decrease on the yield stress promoted by quenching with the crack propagation kinetics. The use of the EWF method\udto characterize the fracture toughness of PLA has allowed to measure this enhancement on toughness, finding that the specific\udessential work of fracture (we) and the plastic term (!wp) parameters increased 120% and 1200%, respectively, after\udthe quenching process.

機(jī)譯：研究了淬火處理對兩種光學(xué)純度不同的兩種聚乳酸（PLA）\商品級熱流延片材擠出薄膜的影響。通過差示掃描量熱法（DSC），拉伸試驗和\斷裂（EWF）方法的基本工作評估了膜的熱和機(jī)械性能，以及斷裂性能。加熱淬火處理會導(dǎo)致老化現(xiàn)象，其中\(zhòng) ud聚合物鏈的自由體積增加，這由玻璃化轉(zhuǎn)變溫度（Tg）的降低以及拉伸剛度和\ udyi屈服應(yīng)力的降低證明。結(jié)果，延展性突然增加，從脆性到延展性，發(fā)現(xiàn)了斷裂行為的顯著變化。在斷裂測試過程中使用應(yīng)變場分析的數(shù)字圖像相關(guān)性（DIC）可以將淬火促進(jìn)的屈服應(yīng)力的降低與裂紋擴(kuò)展動力學(xué)聯(lián)系起來。使用EWF方法來表征PLA的斷裂韌度可以測量這種韌性的提高，發(fā)現(xiàn)斷裂的特定\必要功（we）和塑性項（！wp）參數(shù)分別增加了120％和1200％在淬火過程之后。