Modification of polystyrene and poly(vinyl chloride) for the purpose of obtaining packaging materials degradable in the natural environment

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Abstract

For the purpose of increasing degradability of polystyrene (PS) and poly(vinyl chloride) (PVC), they were modified by means of introducing 1–5% addition of ketone (acetophenone or benzophenone). The influence of UV radiation on thin films of polymers modified in this way was studied. The changes in chemical structure of PS and PVC were studied using UV–vis and FTIR spectroscopy, the degradation reactions were monitored by determining the average molecular weights and polydispersity by gel chromatography, and the crosslinking reactions were estimated by determining the weight content of insoluble gel. The mechanical properties were studied by using standard tensile testing measurements. It was found that the ketones used, acting as sensitizers and/or initiators, caused some considerable changes of photochemical stability of both polymers. The oxidative photodegradation of PS, carried out in the same conditions and presence of the same quantity of modifying additives, is accelerated by a considerably higher rate in comparison to the analogous processes occurring in PVC. The differences in the course of photochemical processes of both irradiated polymers are related to the different miscibility of components. At the same time the limited efficiency of photocrosslinking and only slight deterioration of mechanical properties in PS with added acetophenone or benzophenone suggest the possibility of using such compositions for the manufacture of plastics degradable in natural environment.

Introduction

Poly(vinyl chloride) (PVC) and polystyrene (PS) are, after polyolefins, the most widespread polymers both in industry and everyday life, successfully replacing some natural raw materials.

Plastics from PS and PVC used in the industry of packaging materials make up a considerable share in waste disposed on dumping grounds, therefore, the acceleration of their decomposition is particularly desirable. It is generally known that the following factors induce degradation processes of polymer waste in the natural environment: sun rays, changeable temperature, moisture and humidity, impurities of different kind (including inorganic and organic chemical compounds), as well as bacteria and moulds [1], [2], [3]. Individual specific stages of decomposition are frequently interdependent on each other. Bacteria more easily attack short polymer chains having chemical groups with oxygen atoms (at the ends of, or inside the macromolecules). Branched and crosslinked polymers are, however, less susceptible to biodegradation. Therefore, the course of initial processes induced in polymers by light, heat and moisture is very important for further decomposition of polymer during the attack of microorganisms. It is supposed that some increase of biodegradability of plastics can be attained by exposing them to preliminary irradiation during which the polymer chains become shorter as a result of photodegradation. If the irradiation is carried out in air, some groups containing oxygen atoms (e.g. carbonyl and/or hydroxyl/hydroperoxide) will be additionally built into the structure of the macromolecules as a consequence of photooxidation [4], [5], [6]. Studies concerning this issue have so far been of only a fragmentary character. The constantly growing problem related to the increasing quantities of used packaging made from plastics creates the need for more systematic research in this field to be oriented towards the development of effective, cheap, and ecological ways of utilising the subject waste materials.

The purpose of this work was to study the effect of small contents of low-molecular weight organic substances such as benzophenone or acetophenone on the course of photochemical transformations in films of polystyrene and poly(vinyl chloride). Oxidative photodegradation of PS and PVC modified with the addition of above-mentioned ketones was carried out in accelerated way by using an artificial source of UV radiation.

It is generally known that organic ketones, owing to the presence of Cdouble bondO groups absorbing UV radiation at about 270–280 nm, are one of the more important groups of compounds accelerating photochemical reactions in polymers [6], [7], [8]. Absorption of UV radiation results in the excitation of molecules, which then can undergo decomposition leading to the formation of small active radicals capable of initiating degradation in the given polymer. They may also transfer their excitation energy to the neighbouring macromolecules, which afterwards may undergo some secondary photochemical processes. Both photoinitiation and photosensitisation caused by certain compounds absorbing UV radiation contribute considerably to the increased degradability of polymers, which are by their nature hardly susceptible (or even totally non-susceptible) to photochemical decomposition. The analysis of photochemical processes running simultaneously in polymer samples of different composition, as well as the identification of products of photodegradation, may allow assessment and evaluation of the usefulness of tested organic ketones for obtaining plastics of increased photodegradability, and consequently also of higher biodegradability.

Section snippets

Experimental

The following polymers of Polish make were used in this study: polystyrene—the Chemical Works in Oświęcim, and poly(vinyl chloride)—the Anwil in Włocławek.

Acetophenone and benzophenone (99%) were purchased from Sigma-Aldrich Chemie GmbH, Steinheim (Germany).

The following solvents of high purity, manufactured by the POCH in Gliwice, were used: benzene for PS, and the mixture of tetrahydrofuran (THF)+dichlorobenzene (1:1) for PVC.

For the purpose of obtaining polymer films, 2% (v/m) solutions of

Polystyrene

The course and efficiency of photochemical processes in films of pure polystyrene, as well as in films with 1–5% addition of benzophenone and acetophenone, were studied by spectroscopic methods. The analysis of infrared absorption spectra (Fig. 1) has proved that during the exposure of samples to UV radiation, some small changes take place within the range of appearance of bands corresponding to the stretching vibrations of C–H in the main chain (of methylene CH2 and methine CH groups)

Acknowledgements

Financial support by a grant No. 3T09B 088 18 from the Polish State Committee for Scientific Research (KBN) is gratefully acknowledged.

References (22)

  • A. Torikai et al.

    Polym. Degrad. Stab.

    (1995)
  • B. Mailhot et al.

    Polymer

    (2000)
  • B. Mailhot et al.

    Polym. Degrad. Stab.

    (2000)
  • M. Veronelli et al.

    Polym. Degrad. Stab.

    (1999)
  • A. Torikai et al.

    Polym. Degrad. Stab.

    (1999)
  • U. Gesenhues

    Polym. Degrad. Stab.

    (2000)
  • W.H. Starnes

    Progress in Polym. Sci.

    (2002)
  • Scott G. In: Guillet J. editor. Polymer and ecological problems. N. York: Plenum Press Publishing Corporation; 1973. p....
  • G. Scott et al.

    Degradable polymers. Principles and applications

    (1995)
  • Guillet JE. In: Barenberg SA, Brash JL, Narayan R, Redpath AE. editors, Degradable materials. Boca Raton, FL: CRC...
  • J.F. Rabek

    Polymer photodegradation—mechanisms and experimental methods

    (1993)
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