Elsevier

Desalination

Volume 287, 15 February 2012, Pages 290-300
Desalination

Effects of irradiation with vacuum ultraviolet xenon excimer lamp at 172 nm on water vapor transport through poly(lactic acid) membranes

https://doi.org/10.1016/j.desal.2011.08.026Get rights and content

Abstract

The diffusivity, solubility, and permeability of water vapor and nitrogen were systematically investigated for Vacuum Ultraviolet (VUV)-irradiated poly(lactic acid) (PLA) membranes by a xenon excimer lamp at 172 nm. The photon was completely absorbed in the surface membrane, and the VUV irradiation did not depend on the color center and bulk structure of the PLA membrane. Additionally, surface hydrophilicity increased in the irradiation time range of 0–10 min and settled at a steady state in the irradiation time range of 30–100 min. We discovered the surface photo-oxidation, scission reaction, and crystallization of PLA membranes by VUV irradiation. The PLA chemical structure changed as chain cleavage and formation of Cdouble bondC double bonds and hydroperoxide Osingle bondH at newly formed chain terminals through a Norrish II mechanism. The water vapor permeability of VUV-irradiated PLA membrane for 60 min was equal to that of unirradiated PLA membranes because the water vapor diffusivity reduction for surface crystallization counteracted the solubility enlargement for surface hydrophilicity. The temperature dependence on water vapor permeability of VUV-irradiated PLA membrane at low relative feed pressure showed that diffusivity-controlled behavior and that, at high relative feed pressure, diffusivity- and solubility-controlled behavior.

Highlights

► Surface modification of amorphous PLA was performed with VUV excimer lamp. ► VUV caused surface photo-oxidation, scission reaction, and crystallization of PLA. ► Water vapor permeability at low pressure showed diffusivity-controlled behavior.

Introduction

Poly(lactic acid) (PLA) is an environmentally friendly biodegradable polymer substance with low melting point and good moldability. PLA is used as a material in packaging, electronic, and automobile applications. For such applications, water vapor permeability is an important factor in preventing material degradation because the material is exposed to air during their use.

On the other hand, surface modification technologies have been extensively used in the material industrial fields, and they play an important role in improving general materials [1]. In particular, surface modification by ultraviolet (UV) irradiation has been applied to various materials such as polymers, glasses, ceramics, and metals [2]. For such a surface modification technology, vacuum ultraviolet (VUV) by excimer lamp irradiation enables irradiation in conditions of atmospheric pressure and lower temperature with no damage to the materials. The VUV modification process by excimer lamp is also faster than the low pressure mercury lamp for high generative capacity of oxygen radicals [3]. For such characteristics, this surface modification technology is generally used for the development of the adhesion of materials and surface cleaning [4], [5], [6]. However, the water vapor transport properties of such surface-modified polymer membranes have yet to be studied.

Hence, in the current study, surface modification of PLA membrane was performed with a 172 nm VUV excimer lamp. The effects of VUV irradiation on the bulk and surface properties, as well as their PLA membrane structure were studied. Moreover, the water vapor transport properties (i.e., diffusivity, solubility, and permeability) of VUV-irradiated PLA membrane were systematically investigated. This is the first study on PLA membranes irradiated with VUV xenon excimer lamp at 172 nm and on the water vapor permeation properties of surface-modified polymer membranes.

Section snippets

Preparation of membranes

The PLA membranes were the same samples employed in our previous study [7]. The PLA polymer used in this study had a 4032D product (NatureWorks LLC, Minnetonka, USA). The isomer ratio was in the range of L:D = 96.0:4.0–96.8:3.2. PLA membranes were prepared by casting 2 wt.% dichloromethane solution of each solvent onto a flat-bottomed Petri dish in a glass bell-type vessel, and then drying under atmospheric pressure at room temperature. Each solvent was allowed to evaporate for 48 h. The dried PLA

Membrane bulk characterization

Bulk properties of the VUV-irradiated and unirradiated PLA membrane were systematically studied. The photographs of the PLA membrane for VUV-irradiated and unirradiated PLA membranes are presented in Fig. 1. The UV–vis spectra of these PLA membranes are shown in Fig. 2. The transmittance of their PLA membranes did not change in the 400–700 nm range, and the values were higher than 90%. However, almost no transmittance was found at values below 200 nm. This result indicated that the photon with 172

Conclusions

Surface modification of amorphous PLA membrane was performed by 172 nm excimer lamp irradiation. Water vapor and nitrogen transport properties (i.e., diffusivity, solubility, and permeability) of the VUV-irradiated PLA membrane were systematically investigated. We discovered the surface photo-oxidation, scission reaction, and crystallization of PLA membranes by VUV irradiation. The PLA chemical structural changed as chain cleavage and formation of Cdouble bondC double bonds and hydroperoxide Osingle bondH at newly

References (27)

Cited by (20)

  • Gas separation in polyimide membranes with molecular sieve-like chemical/physical dual crosslink elements onto the top of surface

    2018, Journal of Membrane Science
    Citation Excerpt :

    VUV does not enter into the membrane and can only be modified on the top membrane surface. Previous studies reported the influence of VUV irradiation on the surface characteristics and high-order structure of poly(lactic)acid (PLA) and poly(1-trimethylsilyl-1-propyne) (PTMSP) [9,10]. The reactive hydroxyl groups are thus predicted to form on the top membrane surface by VUV irradiation.

  • Recent advances on the ageing of flame retarded PLA: Effect of UV-light and/or relative humidity

    2017, Polymer Degradation and Stability
    Citation Excerpt :

    This study confirms that the molecular mass is a key parameter in the durability of polymeric materials and especially of flame retarded PLA. The effects of UV light on the degradation of neat PLA have been widely studied over the years [13–15,17–20,46–48]. Depending on the UV irradiation wavelength, two photo-degradation mechanisms have been evidenced.

  • Hydrophilic molecular sieve surface layer formation in hydrophobic poly(1-trimethylsilyl-1-propyne) membranes

    2013, Journal of Membrane Science
    Citation Excerpt :

    In this study, the surface modification of PTMSP membranes was performed with a 172 nm vacuum-ultraviolet (VUV) excimer lamp. VUV irradiation enables irradiation at atmospheric pressure and at low temperature conditions without any damage to the materials, in contrast to the sputtering and vapor deposition technologies [18]. VUV modification by an excimer lamp is likewise faster than that by a low-pressure mercury lamp in terms of the high capacity to generate oxygen radicals [19,20].

View all citing articles on Scopus
View full text