Effects of Citric Acid on Structures and Properties of Thermoplastic Hydroxypropyl Amylomaize Starch Films.

Yang Qin,Hanxue Hou,Yangyong Dai,Wentao Wang,Hui Zhang,Haizhou Dong

doi:10.3390/ma12091565

Abstract

Hydroxypropyl amylomaize starch (HPAS) films were prepared by hot press. The effects of initial pH of HPAS on the mechanical properties, molecular interaction, structure, and cross-linking degree of the resultant films were investigated. A weak acidic condition was suitable for cross-linking of citric acid and HPAS by reactive extrusion. The film of HPAS with an initial pH of 5.66 had the maximum tensile strength of 7.20 MPa and elongation-at-break of 94.53%, and the weight average molecular weight of HPAS increased to 4.17 × 105 g/mol. An appropriate initial pH facilitated the formation of diester bonds between HPAS and citric acid during extrusion, but too low initial pH levels resulted in hydrolysis of starch molecules and reduced the mechanical properties.

Highlights

Starches are promising materials for the preparation of biodegradable plastic and their industrial application can reduce the environmental costs of petroleum-derived materials [1]
The NaOH in hydroxypropyl high amylomaize starch was neutralized and alkali hydrolysis was inhibited, the Hydroxypropyl amylomaize starch (HPAS)-Citric acid (CA) film became colorless with increasing citric acid amount
The cross-linking reaction between citric acid and hydroxypropyl high amylomaize starch was achieved by reactive extrusion while preparing thermoplastic starch

Summary

Introduction

Starches are promising materials for the preparation of biodegradable plastic and their industrial application can reduce the environmental costs of petroleum-derived materials [1]. The poor processability of starch is one of the main reasons that limited the application of starch film. Natural starch granule has a hierarchical periodic structure formed by alternating amorphous and semicrystalline growth rings [3]. This unique lamellar structure makes starch a nonthermoplastic material as the pyrolysis point is lower than the melting point of the crystalline regions [4]. Even some plasticizers (e.g., urea, water, glycerol, glycol, sorbitol, and sugars) are added into starch to disrupt the semicrystalline structure [5]; the starch films remain brittle and have poor mechanical properties compared to low-density polyethylene [6]

Methods

Results

Conclusion