STARCH-G-PLA IN ONE POT PROCESS: THE USE AS A COMPATIBILIZER FOR PLA/TPS BLENDS AND THE DEVELOPMENT OF EXTERNAL STIMULI RESPONSIVE FIBER

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1 STARCH-G-PLA IN ONE POT PROCESS: THE USE AS A COMPATIBILIZER FOR PLA/TPS BLENDS AND THE DEVELOPMENT OF EXTERNAL STIMULI RESPONSIVE FIBER Nathapol Chinivirojsatian a, Autchara Pangon c, Suwabun Chirachanchai* a,b a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand b Center of Excellence on Petrochemical and Materials Technology, Chulalongkorn University, Bangkok, Thailand c National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency, Bangkok, Thailand ABSTRACT Poly(lactic acid) (PLA) is the most feasible biodegradable plastic to be substituted the commodity plastic. However, the limitation are cost and mechanical properties. Starch is a polysaccharide which is inexpensive and renewable. The way to apply starch in plastic products is to modify it to be thermoplastic starch (TPS) by adding glycerol as a plasticizer. TPS can be molten and the price is cheap, it is an ideal candidate additive to reduce cost. TPS was considered as additive for PLA to overcome the brittleness. Therefore, this work proposes the synthesis of starch-g-pla and fabrication of external stimuli responsive fiber. To our idea, starch-g-pla act as a macro-initiator for lactide ring opening polymerization. Moreover starch-g-pla provides the hydroxyl groups to further functionalization with responsive molecule. Here, an introduction of pyrene fluorophore is considered. The present work demonstrate the starch-g-pla functionalized with pyrene is further electrospun to obtain responsive PLA nanofiber. The presentation will include the preparation of starch-g-pla to use as a compatibilizer in PLA/TPS blending and the electrospining to obtain nanofiber with fluorescence responsive properties. *csuwabun@chula.ac.th INTRODUCTION Nowadays, the renewable and biodegradable polymers are attractive materials due to the environmental concerns. Poly(lactic acid) (PLA) is a biodegradable polymer which is comparable to commodity thermoplastics in terms of large scale production, good processibility and high strength, However, PLA has limitations in cost and mechanical properties. Therefore, their developments of PLA are mostly related to the cost reduction and mechanical properties improvement especially brittleness. Starch is a natural abundance polysaccharide which is inexpensive and renewable biopolymer. Thermoplastic starch (TPS) is a form of starch that is plasticized with H-bond formable species, e.g. glycerol to process it as a thermoplastic materials. Thus, TPS is an ideal candidate as an organic additive to reduce cost and improve toughness (Yang et al., 2015). In fact, the improvement of mechanical properties is related to miscibility of blend. But, the direct blend of PLA and TPS causes phase seperation due to thermodynamically immiscible (Longberg et al., 2006). This results in poor mechanical properties of the blend in term of low elongation at break and brittleness materials. To reduce phase separation, modification Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 1

2 of starch or addition of compatibilizers were considered, for examples, the introducing of silane into starch (Jariyasakoolroj et al., 2014), adding of maleic anhydride (Carlson et al., 1999), and adding of starch-g-pla (Chen et al., 2005). Starch-g-PLA is a potential compatibilizer of PLA/TPS blending due to a presence of both characteristics of PLA and starch. In the past, starch-g-pla was prepared by preswelling of starch and then ringopening polymerization of lactide (Chen et al., 2005). However, the multi-step preparation of starch-g-pla is not suitable for large scale production due to the cost and difficulty of solvent removal. Therefore, this work proposes the synthesis of starch-g-pla in one pot reaction without solvent. In our idea, starch-g-pla will be considered in the pathway of lactide ring opening by initiation of hydroxyl group of starch in the presence of tin(ii) octoate catalyst in melt process. Moreover, the use of grafting of PLA on starch via ring opening polymerization of lactide not only potentially improves compatibility between those two polymers but also simultaneously provide available hydroxyl groups for further modifications to use as high value added products Pyrene is a fluorphore used as fluorescent probe to monitor change in physical properties and/or chemical structure of a system. It comes to our view points that starch-g-pla with pyrene labelling will show thermal and humidity response. PLA is responsible for thermal transitions whereas starch is responsible for swelling/shrinking transition. This work proposes an approach to create stimuli-responsive nanofiber from starch-g-pla, and trace its transition in response to external stimuli (temperature and moisture) by labelling with pyrene. This work will cover the preparation starch-g-pla in one pot reaction, the use as compatibilizer in PLA/TPS blending, the fabrication of starch-g-pla with pyrene labelling fiber and also responsive properties. EXPERIMENTAL A. Materials Tapioca starch was purchased from ETC International Trading Co., Thailand. Commercial PLA (2002D) was purchased from Naturework LLC. L-lactide was purchased from Chiang Mai University, Thailand. Tin(II) 2-ethylhexanoate (Sn(Oct) 2, 97% purity), Ƴ-Oxo-1- pyrenebutyric acid, dicyclohexylcarbodiimide and 4-dimethylaminopyridine were purchased from Sigma Aldrich, USA. Chloroform, including HPLC-grade chloroform, and methanol were from RCI Labscan, Thailand. Deuterated chloroform (CDCl 3 ) and dimethylsulphoxide (DMSO) were purchased from Sigma-Aldrich, USA. If not specified, the chemicals in used were analytical grade and used without any further purification. B. Preparation of starch-g-pla Starch-g-PLA was synthesized through ring-opening polymerization of L-lactide and starch by using tin(ii) 2-ethylhexanoate (Sn(Oct) 2 ) as a catalyst. Starch was dried in hot air oven at 60 C for 12 hours to remove moiture. The ring-opening polymerization was carried out at 140 C for 4 hours under nitrogen atmosphere. The purification was done by precipitation in methanol. The precipitate was dissolved in chloroform to remove a homo-pla. The weight feed ratio of starch to lactide is 1:2 to obtained starch-g-pla Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 2

3 C. Melt blending of TPS and PLA with starch-g-pla TPS was prepared by mixing of starch and glycerol (60/40% wt). The PLA/TPS blends done in Barbender mixer using an operating temperature of C, mixing time of 10 min and screw speed for 80 rpm. The TPS contents in PLA/TPS blends were 20/40/60/80 and 100% wt. Starch-g-PLA was used as a compatibilizer and its contents were 1.25, 2.5, 5 and 10 phr. A Wabash compression molding machine was used to compress the products obtained from the mixing. The conditions were preheated at 160 C for 5 min, compressed at 160 C for 5 min at 10 tons loading and cooling 5 min. D. Preparation of starch-g-pla-py 5 g of starch-g-pla, g of DCC ( mol), g of DMAP ( mol), g of Py and 10 ml of DMSO were added to a 50 ml three-naked flask. The mixture reacted first at 0 C for 1 hour and then room temperature for 24 hours under nitrogen atmosphere. The product (starch-g-pla-py) was precipitated in cold methanol. Then crude products was redissolved in DMSO and precipitated again in cold methanol. The product with brown colour was obtained and dried in hot air oven at 60 C for 12 hours. E. Sample prepartation and electrospining of starch-g-pla-py fiber 1.2 g of PLA was dissolved in 4.34 g of DMC and g of starch-g-pla-py was dissolved in 4.34 g of DMF. The PLA and starch-g-pla-py solution were mixed together and continuous stirring. The mixed solution were loaded to a plastic syringe equipped with a 20-gauge metal needle. A high voltage power supply (Spellman CZE1000R) was connected to the needle and grounded plate collector provide an electrical potential at 18 kv. Electrospining of all mixed solutions was carried out at flow rate of 0.05 ml/h with tipto-collector distance of 15 cm. RESULTS AND DISCUSSION A. Structural Characterization The FTIR spectrum of the starch-g-pla show the broad peaks at 3297 and 887 cm -1 corresponded to O-H stretching and pyranose ring of starch, respectively. Meanwhile, the PLA shows peaks at 2990, 1745 and 1350 cm -1 which corresponded to C-H stretching, carbonyl and C-O-H bending, respectively The FT-IR spectra of starch-g-pla shows peaks at 3295, 2987, 1748, 1344 and 887 cm -1 which corresponded to O-H stretching, C-H stretching, carbonyl, C-O-H bending and pyranose ring, respectively. The structural characterization of starch-g-pla are also investigated by 13 C-NMR. Figure 6.2 shows 13 C- NMR spectra with the corresponding carbon resonance signals assigned. This spectra occurring at 17.2 ppm (position a) corresponds to carbon of carbonyl groups (-COCH(CH 3 )OH) and carbon resonance signal at 69.4 ppm corresponds to carbon of methylene group (-COCH(CH 3 )OH in terminal group. B. Compatibility of PLA/TPS blends The compatibility of PLA/TPS blends were observed by SEM and AFM technique. As SEM observation, there are some droplets with voids along the surface in PLA/TPS film (Fig. A(a)). In case of PLA/TPS with starch-g-pla film showed the smooth surface Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 3

4 (Fig. A(b)). This implies the starch-g-pla can improve miscibility between PLA and TPS. The surface of the films was observed by AFM in non-contact mode to confirm compatibility. PLA/TPS film (Fig. B(a)) shows the roughness surface. In case of PLA/TPS with starch-g-pla film (Fig. B(b)) shows the smooth surface and this confirm the less phase separation when starch-g-pla was added. (A) (a) C. Mechanical Properties D. Fluorescence Properties (b) [ type your text here] CONCLUSIONS 50 µm 50 µm (B) (a) (b) Figure 1 (A) SEM micrographs, (B) AFM micrographs (a) PLA/TPS without starch-g-pla film (b) PLA/TPS with starch-g-pla film. E. Mechanical properties The tensile strength and percent elongation at break of PLA/TPS tend to be increased after adding the starch-g-pla as additive. Those mean that the starch-g-pla was used to improve mechanical properties of PLA. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 4

5 Tensile strength (Mpa) Elongation at break (%) PLA PLA/TPS PLA/TPS/Additive Figure 2 The tensile strength and percent elongation at break of the film products from PLA, PLA/TPS film, and PLA/TPS with starch-g-pla. CONCLUSION The objective of the work is to develop the mechanical properties PLA blended with TPS. The work proposes the preparation of the additive by simple melt process and its melt blending. Moreover, the additive can further modification to add function by labelling pyrene molecule. The additive was successfully synthesized by simple reaction and used to blend with PLA and TPS. The tensile strength and percent elongation at break tend to be increased after adding the additive. This implies the additive functions as a compatibilizer for PLA blended with TPS. The additive can reduce phase seperation under the concept of like dissolves like. ACKNOWLEDGEMENTS The authors would like to acknowledge Thailand Graduate Institute of Science and Technology scholarship, the Petroleum and Petrochemical College, Chulalongkorn University, Center for Excellence on Petrochemical and Materials Technology, Chulalongkorn University, for research funds. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 5

6 REFERENCES Carlson, D., Nie, L., Narayan, R., and Dubois, P. (1999). Maleation of polylactide (PLA) by reactive extrusion. Journal of Applied Polymer Science, 72(4), Chen, L., Qiu, X., Deng, M., Hong, Z., Luo, R., Chen, X., and Jing, X. (2005). The starch grafted poly(l-lactide) and the physical properties of its blending composites. Polymer, 46(15), Jariyasakoolroj, P. and Chirachanchai, S. (2014). Silane modified starch for compatible reactive blend with poly(lactic acid). Carbohydrate Polymers, 106( Yang, Y., Tang, Z., Xiong, Z., and Zhu, J. (2015). Preparation and characterization of thermoplastic starches and their blends with poly(lactic acid). International Journal of Biological Macromolecules, 77( Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 6