Alicia Certain

Purdue University

Project Title: Selective Surface Modification of Biopolymers

Advisor: Prof. Jeffrey Youngblood

Introduction

Biopolymers have seen an increase in attention within the last decade because of their natural biodegradability and sustainability. These polymers, produced from plant and microbial factories, differ from traditional polymers, which are typically petroleum based. Advantages of biopolymers over petroleum based polymers include biodegradability, production from a renewable resource, and non-toxicity. Poly(lactic acid) (PLA) and poly(propyleneterephthalate) (PPT) are biopolymers that have gained attention for industrial applications in a variety of uses such as packaging, textiles, and hygiene products. However, these natural polymers in many cases do not have the same material properties as the synthetic polymers. The wettability of the surface is a property of significant importance based on intended application. For example, use in textiles would require an increase in wettability which would increase dyeability and softness of the material, while use in packaging would require a decrease in wettability such that the material would be durable when exposed to moisture.

Project Objectives

  • Surface modification to change wettability
  • Optimization of reaction times

Approach

  • Chemical surface modification
    • APTES modification
    • Addition of 3-aminopropyltriethoxysilane to the surface of the polymers
    • Creates an amine functionalized surface
    • Hydrolysis
    • Immersion in an aqueous alkaline base
    • Creates a hydrolyzed surface
    • Aminolysis
    • Immersion in a lithiated amine (n-lithioethylenediamine)
    • Creates an amine functionalized surface
    • Characterization
    • Contact angle analysis
    • Drop of water on the surface of a material has a characteristic contact angle based on the three interfacial tensions of solid/liquid, liquid/vapor, and solid/vapor
    • Smaller contact angle indicates greater wettability
    • Goniometer and Drop Image Advanced program used to measure contact angle of treated samples
    • AFM imaging
    • Atomic force microscopy used to investigate roughness of treated samples

Findings

  • Aminolysis and hydrolysis were successful techniques in increasing the wettability of PLA
  • APTES modification was successful in increasing the wettability of PPT
  • APTES modification did little to increase the wettability of PLA, however subsequent fluorination was successful in significantly decreasing the wettability
  • Future work
    • More subsequent modifications of functionalized surfaces to decrease wettability rather than increase
    • Further optimization of reaction times
    • Investigation into vapor phase reactions

Figure 1: Untreated PLA, roughness ratio
1.10:1. 1 µm x 1 µm AFM image.
Figure 2: PLA aminolyzed for 2 min, roughness
ratio 1.01:1. 1 µm x 1 µm AFM image.

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