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Film Performance of Poly(Lactic Acid) Blends for Packaging Applications

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RESEARCH ARTICLE Film Performance of Poly(lactic acid) Blends for Packaging Applications PREFACE API 2015 Carlos Diaz Hsun Yi (Sarah) Pao Rochester Institute of Technology Rochester Institute of Technology [email protected] [email protected] Sungyoung Kim Rochester Institute of Technology [email protected] ABSTRACT Poly(lactic acid) (PLA), a biodegradable thermoplastic derived from renewable resources, stands out as a substitute to petroleum-based plastics. PLA based films for food packaging has been an area of both commercial and research interest within the context of sustainability. In spite of its high strength, packaging applications have been limited because PLA is more brittle than traditional oil-based plastics. Because of this, films display low tear and impact resistance and produce a loud crackling sound when manipulated. Although many studies address the toughening of PLA in the bulk, little attention has been placed on the film performance. The present study is aimed at providing a survey of binary PLA based blends with other biodegradable and non-biodegradable plastics. Acrylic impact modifier (AIM, 5 wt. %), ethylene vinyl acetate (EVA, 20 wt.%), polyhydroxyalkanoate (PHA, 10 wt.%), polycaprolactone (PCL, 30 wt.%), polybutylene succinate (PBS, 20 wt.%) and polypropylene carbonate (PPC, 30 wt.%) were each blended with PLA through single-screw extrusion and converted into films via the blown-film process. Tear and impact resistance, heat seal strength, and noise level were measured. EVA, PHA, PCL, and PBS improved the tear resistance with EVA having the highest effect (>2x). Similarly AIM, EVA and PPC improved the resistance of the film to impact-puncture penetration. Heat seal strength was significantly improved by the PHA and moderately increased by AIM (2x) and EVA. Additionally, we proposed a method to quantify the annoyance of the noise made by the films upon manipulation. PCL and PBS significantly reduced the annoyance level of the films. KEY WORDS: polylactic acid, films, packaging, noise measurement, blends Film Performance of Poly(lactic acid) Blends 43 1.0 INTRODUCTION in elongation at break, over 300% compared with <10% for pure PLA [8]. The past decade has witnessed a steady growth Although some studies have addressed the for the market of bio-based and biodegradable resins toughening of PLA through blending, the sample [1], [2]. Plastics are being approached in a more manufacturing and characterization has focused responsible and holistic way, taking into account on thick samples such as dog-bone shape and thick the sources from which they are derived as well as bars for flexural and impact test. Little attention has the ultimate fate of the materials. As the technol- been placed on the film performance. The present ogy evolves, suppliers are able to tailor the polymer study is aimed at providing a survey of binary PLA to specific applications by controlling the molecular based blends with other biodegradable and non-bio- weight and molecular architecture. As a result, new degradable plastics with the ultimate goal of identi- and improved grades of bioplastics resins are con- fying blend systems with the potential for property tinuously being introduced in the market. improvement targeting specific applications. The Polylactic acid (PLA) is at the forefront of com- material selection focused on newer resins with mercially available bioplastics. PLA is derived from high molecular weight intended for thermoplastic renewable resources and biodegradable. PLA based applications. The manufactured films were evalu- films for food packaging has been an area of both ated in terms of tensile properties, tear and impact industrial and research interest within the context resistance and heat seal strength. Additionally, of sustainability [3]. In spite of its excellent prop- noise level produced by the film upon manipulation erties, packaging applications have been limited was recorded and analyzed. because PLA’s brittle behaviour. Because of this, films display low tear and impact resistance, low 2.0 EXPERIEMNTAL elongation, and produce a loud crackling sound when manipulated. Different approaches have been proposed to 2.1 Materials overcome the brittleness of PLA including copoly- Table 1 lists the materials used in this study merization, plasticization and blending with other as well as the relative blend compositions (Ratio polymers [4]. Copolymerization is not economically by mass). Blend compositions were selected based viable unless produced in a large industrial scale. on a literature review and suppliers recommenda- Plasticization requires large amounts of plasticiz- tions for the case of AIM. Polylactic acid, Ingeo ers to achieve flexibility that can leach out after the 4043 D, was purchased from Natureworks, LLC. material is manufactured [5]. On the other hand, Acrylic impact modifier (AIM), Paraloid BPM 515, blending with other polymers is a convenient way was obtained from DOW Chemical Company. Eth- to modify the properties. Polyhydroxybutyrate ylene-vinyl acetate copolymer, Levamelt 500, was (PHB) [6], Popycaprolactone [7], poly(ethylene-co- supplied by Lanxess. The copolymer contains 50 vinyl acetate) (EVA) [8], among other resins have wt % vinyl acetate. Polyhydroxyalkanoate, M-vera been blended with PLA to improve toughness. Ma B5008, was supplied by Metabolix. Polycaprolac- and coworkers found that the compatibility between tone (PCL), CAPA FB 100, was kindly donated PLA and EVA could be adjusted by varying the vinyl by Perstorp. CAPA FB 100 has a slightly crossed- acetate (VA) content on EVA. Copolymers with 50 linked structure with a molecular weight of 100,000 wt.% VA content showed the highest improvement Daltons. Polybutylene succinate (PBS) Bionelle Journal of Applied Packaging Research 44 Table 1: Blend formulations information. MFI measured at 210°C and 2.16 kg Blends MFI Ratio Additive Full Name Target Level (g/10min) by Mass PLA 5.2 100:00 Natureworks 4043D PLA / AIM 6.1 95:05 Acrylic Impact Modifier Paraloid BPM-515 PLA / EVA 6.4 80:20 Ethylene co-vinyl acetate Lanxess Levamelt 500 PLA / PHA 7.5 90:10 Polyhydroxyalkanoate Metabolix Mirel P5001 PLA / PCL 9.3 70:30 Polycaprolactone Perstrop CAPA FB 100 PLA / PBS 21.0 80:20 Polybutylene succinate Showa Bionelle 1001MD PLA / PPC 5.7 70:30 Polypropylene carbonate Novomer 1001MD was supplied by Showa Denko America, Specimens were carefully selected and cut to 1” x Inc. Polypropylene carbonate (PPC) was kindly 6” strips with the machine direction. donated by Novomer. Tear resistance was determined according to ASTM D 1922 standard using an Elmendorf-type 2.2 Melt mixing and film manufacturing tester (200g pendulum). Test specimens in both Melt mixing of the components was carried machine direction and cross direction were cut out on a single-screw extruder (Wayne Machine & to 2.5” x 3” with a template such that the direc- Die Co.) followed by pelletizing. The temperature tion of the tear would be parallel to the 2.5” side. profile used, from die to feed throat, was 390, 390, A machine direction specimen is defined such that 380, 375, 375, 355, and 320 °F. Only for the PLA/ the direction of the tear is parallel to the machine EVA blend the profile was adjusted to 335, 335, 330, direction. Spencer Impact resistance of the films 310, 280, 250, and 120 °F. was measured according to ASTM D3420 proce- Films were manufactured in a LabTech blown dure B on a Thwing-Albert’s Protear Elmendorf film laboratory line (390 to 360 °F). Blown film Tear & Spencer. A 1600 grams pendulum was use conditions (i.e., blow up ratio, rotational screw for the test. speed) was adjusted targeting a nominal thickness The potential of using PLA and PLA blends as of 1.5 mils. All the materials were pre-dried before heat seal layers was investigated by determining the mixing and blown film process. heat seal strength (ASTM F88-06). Fin seals were produced on a Sencorp Bar Heat Sealer 24 AS/1 2.3 Testing using temperatures ranging from 120 to 140 °C for Tensile testing of all samples was performed on 1 second. an Instron 4301, 43K1 tensile tester with 5 kN load PLA films are known for producing a loud cell and pneumatic grips. The initial gauge length noise upon manipulation, which has been proved was set to five inches and a crosshead speed of 0.5 an undesirable characteristic in packaging applica- inch/min was used according to ASTM D 882-02. tions. Film samples of 9.5 by 9.5 inch squares were Film Performance of Poly(lactic acid) Blends 45 cut for noise characterization. At least four repli- 2.4 Results and Discussion cates of each sample were tested. Manual manipu- Table 2 shows the modulus of elasticity, tensile lation of the films was done in a recording studio at strength, elongation at break and impact resistance RIT (reverberation time is about 0.3 sec at 500 Hz). of the samples. The thickness in the last column is The noises from the films have been recorded using the average of 10 samples. All the blends decreased a Brüel & Kjær head-and-torso-simulator (HATS) the modulus of elasticity but only the changes model 4100. This simulator is a special microphone produced by EVA, PCL and PBS were statistically that captures precise psychoacoustic information as significant. The results were anticipated because a human hears. Among many psychoacoustic attri- EVA PCL and PBS are flexible and rubberlike (low butes, perceived “annoyance” should be the most modulus) imparting flexibility to the blends as the important attribute to be considered in manufac- content increase. Similarly, a decrease in tensile turing a film since high annoyance may degrade strength was observed in the PLA/PCL and PLA/ usability of a film by imposing negative impression. PBS blends. In the current analysis, the authors used the annoy- Only some of the blends showed a marginal ance prediction model proposed by Carletti et al.
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