WO2006010233A1

WO2006010233A1 - Photodegradable films derived from polyethylene

Info

Publication number: WO2006010233A1
Application number: PCT/BR2004/000137
Authority: WO
Inventors: Marco Aurélio DE PAOLI; Ralf Giesse
Original assignee: Universidade Estadual De Campinas - Unicamp
Priority date: 2004-07-29
Filing date: 2004-07-29
Publication date: 2006-02-02

Abstract

This patent describes a process to obtain Low Density Polyethylene (LDPE) film derivatives via the sorption of acrylic and vinyl acetate monomers by the polyethylene matrix, followed by the photo-polymerization of the soaked material. The method provided thin films, in which a vinyl acetate or acrylic polymer is blended in the polyethylene matrix in very small quantities (in concentrations from 1 to 2 %), with no material deposited on the surface. These films showed through transmittance and reflectance (attenuated total reflectance, ATR) infrared spectra and visible-UV spectrophotometry that: 1) the greater photo-degradability of LDPE/PX [PX means PAA for poly(acrylic acid), PEA for poly(ethyl acrylate), PMA for poly(methyl acrylate), PMNA for poly(methyl metacrylate), and PVA for poly(vinyl acetate)] compared to pure LDPE; 2) the beginning of the photo-degradation being registered in the bulk of the films and not on their surface; and 3) a significative mass loss during the photo-degradation. Regarding the mechanical properties according to ASTM D 882 standard, the LDPE/PAA films gave stress at failure and elongation at break values similar to pure LDPE, while the ones obtained by LDPE/PX (X=EA, MA, MMA and VA) were smaller values (from 25 to 30% smaller). Photo-degraded samples of LDPE/PX (X=EA, MA, MMA and VA) gave stress at failure and elongation at break ca. 50% smaller values than the ones obtained by photo-degraded pure LDPE films. At the half lifetime of pure LDPE under UV radiation, the LDPE/PX film samples (X=AA, EA, MA, MMA and VA) were already brittle. The results show that the introduction of the second component in the studied matrix made it possible to obtain photo-degradable polymer films derived from pure polyethylene, which can help to solve problems like, for instance, plastic residues in interaction with the environment.

Description

PHOTODEGRADABLE FILMS DERTVED FROM POLYETHYLENE

The invention deals with the application of acrylic polyesters into low-density polyethylene (LDPE) films, which is a polymer commercially used in packaging materials. This invention serves to reduce LDPE lifetime under solar light (ultraviolet radiation) after its use, i.e., to turn it into a photodegradable LDPE, i.e., degradable under solar light or ultraviolet (UV) radiation.

Our invention enabled the production of derived films from LDPE, in a simple way, with usable life reduced by half, under UV radiation, compared to pure LDPE. However, the existing processes in the market don't reveal the necessary amount of time, for their respective invented plastics being completely photodegraded, a part from the fact that their processes present more production steps. BACKGROUND OF THE INVENTION

One of the processes, which exist nowadays in the market in the same invention area, is the making of modified plastic granules for producing plastic biodegradable films, involving the composition of carbohydrates with polymeric additives at high temperatures and the granulation in a special projected extruder. Technical problems, although minimized, found are of blocking pipes and of suffering fungi, algae and bacterial attack. Another process of biodegradable and photodegradable plastic films production involves the composition of plastic filler to prepare plastic films, which contain inorganic oxide powders and a polymeric resin (3). Technical problems presented were worker exposure risks in the handling of the inorganic oxide powders, extremely hazardous to health.

Another invention describes a composition, which includes modified starch, photosensibilizer, degradation controlling agent and talcum powder, to produce biodegradable and photodegradable polyethylene (4). Evaluated technical problems were in the manipulation of aluminum-titanium coupling agents, to treat starch and talcum powder, the latter offering exposure risk. Another process presents the formation of a basic material capable of suffering under light and biological degradation, which includes polyolefin resin, modified starch, photodegradation agent, oxidation accelerator, auto-oxidation agent, degradation controlling agent and calcium carbonate (5). It was not informed how much polyethylene useful lifetime was reduced.

Another variation shows the preparation of a degradable additive composed material for polyolefinic resins, which contains an polyhydroxi-carbonyl aliphatic acid (citric acid or monosodic citrate), a metal carboxilate (preferably cobalt stereate), and stabilizers compounds or oxidants (calcium oxide and iron oxide pigments), specially for the use in bin and agricultural application bags (6). One improvement in relation to the previous patent involves the polyolefinic resin production containing degradable additives and in their composition: a metallic carboxilate, a polyhydroxi-carboxylic acid and an iron oxide pigment (7). This invent is used in polymers to make dustbin bags, shop bags, material for disposable napkins, packaging films, films for using in agriculture, etc. The last two invents present technical problems as exposure risks to employed oxide and iron oxide pigment dusts.

Thus, it would be interesting to develop a photodegradable plastic that could not suffer fungi, algae or bacterial attack; could not need the manipulation with inorganic oxide dusts, nor with aluminum-titanium coupling agents; and could not need the exposure to iron oxide pigments, as described above.

SUMMARY OF THE INVENTION

The present invention presents less amount of ingredients for producing the photodegradable films derived from LDPE, by only sorbing the pure LDPE into the liquid monomer containing the dissolved photoinitiator, followed by its photopolimerization in the LDPE matrix. As this photodegradable material has no natural fibers nor starch in it, it does not suffer microorganisms attack during its use before being discarded. Furthermore at the half lifetime of pure LDPE under UV radiation, the derived film samples were already brittle. DESCRIPTION OF THE INVENTION

Our method supplied thin films, in which a vinyl and acrylic polymer is inserted in the LDPE matrix, in small amounts (from 1 to 5 % by weight), with no material deposited on the surface. The used monomers were: acrylic acid (AA), ethyl acrylate (EA), methyl acrylate (MA), methyl metacrylate (MMA), and vinyl acetate (VA). In this research it was studied how the photochemical modification in the LDPE affects in its photodegradation compared to the pure LDPE. This was motivated by the fact that the oxygen transport properties in the different compositions (LDPE/PAA, LDPE/PMA, and LDPE/PVA) are significantly altered in relation to pure LDPE. Samples of pure LDPE and LDPE/PX (X = AA, EA, MA, MMA, and VA) films, of approximately 100

μm thickness, were prepared triplicate for studying the photodegradation in experiments

of exposure to UV radiation (medium pressure mercury vapor lamps with main emission at 254 nm, with average intensity of 1.7 mW/cm² and average energy of 0,018 J/cm², both measured 10 cm from radiation source) at room temperature. These films show through differential transmittance infrared spectrophotometry and ATR (attenuated total reflectance) and differential UV/visible spectrophotometry that: 1) a greater photo degradability of LDPE/PX in relation to pure LDPE, 2) the beginning of the photodegradation registered inside the films and not on the surface, and 3) the significant loss of mass of the LDPE/PX films during the photodegradation. In the case of pure LDPE, the carboxylic acid is the chemical species present in more proportion (circa 50 %) as a product of photodegradation compared to ketone, aldehide, etc. The benzophenone, used as a photoinitiator in the process of photopolymerization of the monomer X, is not responsible for the initiation of the photodegradation of the LDPE/PX films, because it is totally consumed in the preparation of the materials by photochemical polymerization. Regarding the mechanical properties according to ASTM D 882 Standard, the LDPE/PAA films presented stress strain and relative elongation values similar to pure LDPE, while the ones obtained by LDPE/PX (X = EA, MA, MMA, and VA) presented smaller values. As it would be expected, photodegraded LDPE/PX (X = EA, MA, MMA, and VA) samples showed stress train and relative elongation values circa 50 % smaller than the photodegraded ones of pure LDPE. By reaching half lifetime of pure LDPE under UV radiation, the samples of LDPE/PX (X = AA, EA, MA, MMA, and VA) films were already brittle.

The polyethylene plastics absorb the acrylic monomers, passing under UV radiation for 0 to 5 hours, for the photopolymerization of these monomers in the LDPE matrix. These plastics, containing now the acrylic polyesters, are employed as packaging materials, always protected from solar or UV irradiation. When discarded, they must be exposed to the sun or to UV irradiation, to undergo the photodegradation process. The photochemical degradation of pure LDPE occurred in a 500 to 1000 h period, while of LDPE/PX films occurred from 250 to 500 h. The pure LDPE needs several decades to degrade in the environment. The introduction of a second component, PX, in the studied matrix enabled us to obtain photodegradable polymeric films derived from pure LDPE, and all of it will allow helping the resolution of problems, such as of plastic residues in interaction with the environment. The greater photodegradability of LDPE would lead to the formation of lower molar mass fragments, and we can predict that this pretreatment would turn LDPE more easily degradable. References- Pryor Art:

1) M. I. Felisberti, R. Giesse, M. -A. De Paoli, Polym. Bull., 13, 163 (1985).

2) S. S. Nevgi, Patent Number AU200150642-A; WO200168744-A2.

3) Y. K. Ko, Patent Number AU9950683-A; WO200031166-A1. 4) C. Liu, X. Liu, Patent Number CN1242390-A.

5) X. Zhao, Patent Number CN1193026-A,

6) R. A. Garcia, J. G. Gho, Patent Number NZ286678-A.

7) R. A. Garcia, J. G. Gho, Patent Number AU730451-B; AU9654537-A; NZ286678- A..

Claims

1 PHOTODEGRADABLE FILMS DERIVED FROM

POLYETHYLENE, characterizing by comprising the production of them by sorbing the acrylic esters and vinyl monomers in the polyethylene matrix, followed by its photopolymerization.

2. PHOTODEGRADABLE FILMS DERIVED FROM

POLYETHYLENE according claim 1 having less amount of ingredients for producing these photodegradable films, by only sorbing the pure polyethylene into the liquid monomer containing the dissolved photoinitiator, followed by its photopolimerization in the LDPE matrix.

3 PHOTODEGRADABLE FILMS DERIVED FROM

POLYETHYLENE, according claim 1 characterizing by the fact that the lifetime of these thermoplastics is reduced by half under ultraviolet radiation compared to the thermoplastics without the above mentioned treatment.

4 PHOTODEGRADABLE FILMS DERIVED FROM

POLYETHYLENE according claim 1 containing a small amount of the second component in the polyethylene matrix, which is enough to turn the films efficiently photodegradable.

5. THE METHOD SUPPLYING THIN PHOTODEGRADABLE FILMS DERIVED FROM POLYETHYLENE, in which a vinyl and acrylic polymer is inserted in the LDPE matrix, by sorbing the liquid acrylic esters and vinyl monomers, containing respectively the dissolved photoinitiator, in the polyethylene matrix, followed by its photopolymerization, yielding small amounts (from 1 to 5 % by weight), with no material deposited on the surface. The used monomers were: acrylic acid (AA), ethyl acrylate (EA), methyl acrylate (MA), methyl metacrylate (MMA), and vinyl acetate (VA), and other monomers of the same organic functional groups. Samples of pure LDPE and LDPE/PX (X = AA, EA, MA, MMA, and VA) films, from

approximately 50 to 300 μm thickness, were prepared for studying the photodegradation

in experiments of exposure to UV radiation (preferably medium pressure mercury vapor lamps with main emission at 254 nm, with average intensity of 1.7 mW/cm² and average energy of 0,018 J/cm², both measured 10 cm from radiation source) at room temperature.