Effect of Extrusion Screw Speed and Plasticizer Proportions on the Rheological, Thermal, Mechanical, Morphological and Superficial Properties of PLA.

Jaime Gálvez,Bairo Vera Mondragón,Miguel A Hidalgo Salazar,Juan P Correa Aguirre,Carolina Caicedo,Elizabeth Wagner

doi:10.3390/polym12092111

Abstract

One of the critical processing parameters—the speed of the extrusion process for plasticized poly (lactic acid) (PLA)—was investigated in the presence of acetyl tributyl citrate (ATBC) as plasticizer. The mixtures were obtained by varying the content of plasticizer (ATBC, 10–30% by weight), using a twin screw extruder as a processing medium for which a temperature profile with peak was established that ended at 160 °C, two mixing zones and different screw rotation speeds (60 and 150 rpm). To evaluate the thermo-mechanical properties of the blend and hydrophilicity, the miscibility of the plasticizing and PLA matrix, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), oscillatory rheological analysis, Dynamic Mechanical Analysis (DMA), mechanical analysis, as well as the contact angle were tested. The results derived from the oscillatory rheological analysis had a viscous behavior in the PLA samples with the presence of ATBC; the lower process speed promotes the transitions from viscous to elastic as well as higher values of loss modulus, storage modulus and complex viscosity, which means less loss of molecular weight and lower residual energy in the transition from the viscous state to the elastic state. The mechanical and thermal performance was optimized considering a greater capacity in the energy absorption and integration of the components.

Highlights

Commercial grade acetyltributyl citrate (ATBC) with a density of 1.05 g/cm3 and purity < 99% was purchased from SUCROAL S.A
The samples were abbreviated as PLAX-Y with X = extrusion screw speed and Y = acetyl tributyl citrate (ATBC) proportion is enough, for example, PLA60-20 is a poly-lactic acid (PLA) obtained at 60 rpm screw speed and Y = ATBC proportion is enough, for example, PLA60-20 is a PLA obtained at 60 rpm and and containing
The curves corresponding to the storage and loss modulus were analyzed according to the angular frequency for the target samples in this study (PLA, PLA: ATBC), which are presented in Figures 2 and 3

Summary

Introduction

There is a great need to resolve problems associated with the high consumption of non-renewable resources, to produce non-degradable polymers, which is generating a high amount of plastic waste [1]; biodegradable aliphatic polymers, such as poly-hydroxyalkanoates (PHAs), poly-butylene succinate (PBS), poly-butylene succinate-co-adipate (PBSA), poly(butylene adipate-co-terephthalate) (PBAT) or poly-lactic acid (PLA), are an important alternative [2,3,4].Among these biopolymers, PLA is the key and promising biopolymer to develop new materials both in industry and in academy [5], commercially is the most traded and it is obtained from the fermentation of renewable sources such as whey, corn, potato, molasses, or sugar feed stocksPolymers 2020, 12, 2111; doi:10.3390/polym12092111 www.mdpi.com/journal/polymersPolymers 2020, 12, 2111 to produce the monomer lactic acid [6,7], which is subsequently polymerized to a linear aliphatic thermoplastic polyester by a ring-opening synthesis procedure [8].PLA possesses interesting features, such as sustainability, relatively easy processing, the capacity for heat sealing, high transparency, gloss, printing ability [2]; it has excellent optical properties and high tensile strength but, it is rigid and brittle [9]. There is a great need to resolve problems associated with the high consumption of non-renewable resources, to produce non-degradable polymers, which is generating a high amount of plastic waste [1]; biodegradable aliphatic polymers, such as poly-hydroxyalkanoates (PHAs), poly-butylene succinate (PBS), poly-butylene succinate-co-adipate (PBSA), poly(butylene adipate-co-terephthalate) (PBAT) or poly-lactic acid (PLA), are an important alternative [2,3,4]. Among these biopolymers, PLA is the key and promising biopolymer to develop new materials both in industry and in academy [5], commercially is the most traded and it is obtained from the fermentation of renewable sources such as whey, corn, potato, molasses, or sugar feed stocks. The plasticization process should, at the optimal percentage of the biocompatible plasticizer, be compatible with the PLA, stable at the processing temperatures, reduce the glass transition of the polymeric amorphous domain, reducing the melting point of the crystalline phase, all this to enhance the molecular mobility of the PLA chains [9,14,15,16,17]

Methods

Results

Conclusion