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bioplasticsMAGAZINE_1306

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bioplasticsMAGAZINE_1306

People Films | Flexibles

People Films | Flexibles | Bags New heat-resistant By Mohammad Kazem Fehri a , Patrizia Cinelli a , Thanh Vu Phoung a , Irene Anguillesi a , Sara Salvadori a , Monia Montorsi b , Consuelo Mugoni b , Stefano Fiori c , Andrea Lazzeri a a Inter University Consortium Materials Science and Technology (INSTM),University of Pisa Pisa, Italy b University of Modena and Reggio Emilia Modena, Italy c Condensia Química S.A Barcelona, Spain uring the last decade, among biodegradable and biocompatible polymers, polylactic acid PLA has been considered as a potential alternative for synthetic plastic materials on the basis of its good processability, and relatively low cost. However applications using conventional PLA are limited by low mechanical properties, poor thermal stability and a slow crystallization rate. In particular amorphous PLA is not suitable for packaging of hot-filled food or beverage bottles or other containers, i.e. filled at the food-manufacturing or beveragebottling plant while the food or beverage is still hot from pasteurization. Examples include tomato ketchup or some kinds of fruit juice. In order to modify some of the limitations in properties, additives such as plasticizers, coupling agents and fillers can be used. As part of the EC Project DIBBIOPACK (Development of injection and extrusion blow moulded biodegradable and multifunctional packages by nanotechnologies), the project team considered the use of a biodegradable plasticizer, GLYPLAST OLA8, (a low molecular weight modified PLA produced from renewable raw materials by Condensia Quimica, Spain), in combination with two nucleating agents, PDLA and LAK301. To compare the relative effectiveness of PDLA and LAK301 (LAK) the crystallization time of PLA in the blends was measured since this in an extremely important parameter in polymer processing and in industrial production. Using a DoE (Design of Experiments) approach, a mixture design was prepared to study the effect of OLA8 as a plasticizer and of LAK301 and PDLA as nucleating agents on the time to reach 50% of crystallization of PLLA in the blends. Some of the studied blends are reported in Table I. Tensile tests were performed with an Instron 4302 at room temperature and with a crosshead speed of 10 mm/min. Dynamic Mechanical Thermal Analysis (DMTA) was carried out by means of a GABO Eplexor 100N. Table I: Compositions Sample Code Composition in Weight [%] PLA OLA8 LAK PDLA STD 1 90 10 - - STD 2 78.2 20 - 1.8 STD 3 72.2 20 2.8 5 STD 4 70 20 5 5 STD 5 75 20 5 - Table II : Mechanical properties STD Composition by weight [%] Mechanical Properties E [GPa] σ y [MPa] σ U [MPa] ε b [%] STD1 (PLA-OLA8 10) 2.7 47 38 5.6 STD2 (PLA 78.2-OLA8 20 - PDLA 1.8) 1.24 16 23 310 STD3 ( PLA 72.2 - OLA 20 - LAK 2.8 - PDLA 5) 2 18 23 285 STD4 ( PLA 70 - OLA8 20 - LAK 5 - PDLA 5) 1.2 11.2 20 278 STD5 ( PLA 75 - OLA8 20 - LAK 5 ) 2.2 28 18 247 (E: Modulus of elasticity, σ y : yielding stress, σ U : ultimate stress, ε b : elongation at break) 26 bioplastics MAGAZINE [06/13] Vol. 8

From Science & Research PLA blends (310%) in presence of 20 % by wt OLA8 and 1.8 % by wt PDLA (STD2) attest for a good interaction among all components that induce good dispersion, with no phase separation. While the addition of a plasticizer normally causes a drop in storage modulus the concurrent addition of a nucleating agent such as LAK leads to a higher degree of crystallinity and to an improvement in elastic modulus. In Table III, interesting values can be observed in terms of percent crystallinity, evaluated from melting enthalpy, glass transition temperature and crystallization kinetic, for the blend based on OLA8 20 % by wt, LAK 2.8 % by wt PDLA 5 % by wt (STD3). Dependence between the time of crystallization and the type of nucleating agent, LAK301 versus PDLA; and the relative amounts was observed. By this study it can be seen that both PDLA and LAK reduce the time of crystallization but the LAK seems to have a more relevant effect. In conclusion, LAK and PDLA are efficient nucleating agents for PLA. The effect of LAK is higher than the effect of PDLA. Fine tuning of the type and/or amount of nucleating agent can allow us to control the time of crystallization and adapt it to the industrial requirements. OLA8 confirmed to be an efficient plasticizer for PLA. For production of heat resistant packaging based on PLA the formulation including PLA, OLA8 (20 % by wt), and LAK (5 % by wt) exhibited relatively good values of elongation at break, associated with a reduced time of crystallization, and a moderate content of nucleating agent (5%). Table III : Thermal properties STD Compostion by weight [%] t 1/2 [sec] ΔH m [J/g] ΔH c [J/g] Cryst. [%] STD 1 (PLA-OLA8 10) n.d. 1.5 23.4 25.1 STD 2 (PLA 78.2-OLA8 20 - PDLA 1.8) 152 4.3 21.4 23.0 STD 3 ( PLA 72.2 - OLA 20 - LAK 2.8 - PDLA 5) STD 4 ( PLA 70 - OLA8 20 - LAK 5 - PDLA 5) 46 6.8 12.2 13.1 48 6.1 14.7 15.9 STD 5 ( PLA 75 - OLA8 20 - LAK 5 ) 61 3.9 16.2 17.4 (t 1/2 :half time crystallization, ΔH m : melting enthalpy, ΔH c : crystallization enthalpy, Cryst: percent crystallinity, n.d.: not determined) www.dibbiopack.eu bioplastics MAGAZINE [06/13] Vol. 8 27

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