Reactivity of weathered polyolefinic samples studied by means of TGA

Accepted Manuscript Reactivity of weathered polyolefinic samples studied by means of TGA Raffaele Gallo, Febo Severini PII:

S0141-3910(17)30210-0

DOI:

10.1016/j.polymdegradstab.2017.07.020

Reference:

PDST 8299

To appear in:

Polymer Degradation and Stability

Received Date: 4 July 2016 Revised Date:

6 July 2017

Accepted Date: 18 July 2017

Please cite this article as: Gallo R, Severini F, Reactivity of weathered polyolefinic samples studied by means of TGA, Polymer Degradation and Stability (2017), doi: 10.1016/j.polymdegradstab.2017.07.020. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT REACTIVITY OF WEATHERED

POLYOLEFINIC SAMPLES STUDIED BY MEANS OF TGA

Raffaele Gallo a,*, Febo Severini b,1 Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Università di

Messina, Viale F. Stagno d’Alcontres, 31, 98166 Messina, Italy b

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a

Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. *Natta”, Politecnico di

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Milano, Piazza Leonardo da Vinci, 32, 20133 Milano, Italy

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ABSTRACT

The reactivity of polyolefin films having different environmental exposure times was assessed by thermogravimetric curves. Tests in air at 200°C of all polyethylene samples show an initial steady weight time, an intermediate weight increase due to oxygen absorption and,

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subsequently, a continuous weight loss. The highest weight gain is obtained with weathered samples containing many oxygenated functional groups. In the same conditions no polypropylene sample displays the intermediate weight increase. Thermogravimetric data can

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be used to determine how the environmental stress affects oxidation, crosslinking and scission reactions in pristine and recycled polyolefins. Furthermore, the concept of induction time of

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the degradation can be redefined.

Keywords: weathered polyolefins, thermogravimetry, reactivity increase, degradation mechanism, induction time, natural aging.

*

Corresponding author. Tel.: +39 090 393134; fax: +39 090 391518. E-mail addresses: [email protected], [email protected] (R. Gallo). 1 Now retired. 1

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1. Introduction

The studies concerning environmental and artificial degradation of polyolefins are based on analytical methods which measure changes of the samples during aging. Time courses of

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these changes suggest that the instability of the macromolecules rises during the aging process. Usually the increasing instability is ascribed to the radical auto-oxidation mechanism in which peroxides and hydroperoxides play a key role [1,2]. Therefore the level of

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degradation of the specimens is mainly evaluated by methods related to oxygen inclusion in the polymeric structure, such as IR spectroscopy, oxygen uptake, chemiluminescence,

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titration of peroxide compounds. Results show that most natural and accelerated aging and photo- and thermo-oxidation tests are characterized by an initial time having constant values of the quantities under examination [3-7]. In the case of polypropylene, carbonyl detection by infrared spectroscopy is not the absolute probe to measure the photooxidation [8]. Moreover other features used to monitor the degradation process of polyolefins, such as molecular

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masses and mechanical properties, change after an initial period without variations [9,10]. So the induction time for the onset of an alteration path in a material has a limited value because

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it depends on the measured quantity and the aging type. Some studies have suggested an infectious model based on sample heterogeneity to justify time courses of reactions triggered

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by hydroperoxides [11,12]. It is evident that there is interest to evaluate the induction period for the occurrence of oxygenated groups according to the chemical structure of the polyolefin and the aging type. In fact, this may increase the knowledge on the interaction between atmospheric oxygen and macromolecular structures and the starting mechanism of the oxidative degradation with clear practical aspects on the stabilization of materials. However, the relationship between the incorporation of oxygen and the temporal variations of other important characteristics of weathered polyolefins needs to be investigated, in order to obtain a more satisfactory framework of the stability differences under real conditions.

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Studies based on the previously mentioned methods are indirect because they do not measure the reactivity of macromolecular systems, but provide indications of specific chemical or physical features of the samples that can be considered causes and/or effects of instability. A more direct method to test the reactivity of the individual weathered samples is to compare

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their behavior in surely reactive conditions for these organic structures, but not so extreme as to cancel the differences. A simple and reliable system is to study the changes in the behavior of the sample weight in air at a sufficiently high temperature, such as to highlight the

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reactivity of any modification introduced by aging. With this type of approach the induction time can be defined as an initial aging stage which does not introduce significant elements of

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instability. That is, a difference in weight changes in reactive conditions requires a characteristic initial time of aging, sufficient to introduce a critical concentration of structural anomalies. Even with this method the induction time depends on the initial macromolecular structure and the type of aging, however it is influenced by all possible causes of instability, even those that do not involve oxygen incorporation. Some works have already shown

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induction times by measuring the mass change as a function of degradation time, but the measurements were conducted at room temperature and therefore provide information on the

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incorporation of atmospheric oxygen, as an alternative to spectroscopic methods. Furthermore, these data refer to artificial tests of photo- and thermo-oxidation [13,14].

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Aim of this work is the study of weight changes at 200° C in air of polyolefin films having different environmental exposure times. Relations between exposure times and reactivity of the samples in the thermobalance are analyzed. Some mechanisms of the degradation process are proposed on the basis of the results.

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2. Experimental

2.1. Materials

polyethylene (LDPE) films used for greenhouse covering and stabilized with about

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0.2% of a mixture of Irganox 1076, a hindered phenol and a derivative of benzophenone; characteristics: density = 0.919 g cm-3, average thickness = 145 µm,

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average molecular weight Mw = 156,700 Da;

a set of six LDPE samples including a variable recycled amount, that is: 0%, 10%, 25%,

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78%, 91% and 100%;

biaxially oriented isotactic polypropylene (iPP) films not stabilized to light; characteristics: density = 0.873 g cm-3, average thickness = 26 µm, average molecular weight Mw = 328,000 Da;

three films of ethylene/octene copolymers (Affinity polymers: PL1880, VP8770 and

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EG8150) containing few p.p.m. of stabilizers; characteristics: density = 0.902 g cm-3 (PL1880), 0.885 g cm-3 (VP8770), 0.868 g cm-3 (EG8150); average thickness = 110 µm

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(PL1880), 90 µm (VP8770), 95 µm (EG8150); X ray crystallinity = 28.5% (PL1880),

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17.5% (VP8780), 14.8% (EG8150).

2.2. Weathering

All the samples were exposed in Messina, Italy (38° 11’ 20’’ north, 15° 33’ 30’’ east, 59 m from sea level). The samples were mounted on wooden frames inclined at 45° with respect to the horizon and were exposed facing southwest on a terrace at about 20 m above the ground.

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2.3. TGA

The weight changes of the pristine films and of the aged samples were obtained by thermogravimetric analysis (TGA) with isothermal curves in air at 200° C on a TGS-2 Perkin-

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Elmer thermobalance. Preliminary tests have shown that samples weighing less than 10 mg, cut as discs from the exposed films, at 200°C are melted and give reproducible results, regardless of polyolefin type and exposure hours. Samples in the form of discs (5-10 mg)

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were rapidly heated at 160°C min-1 up to 200°C and kept there monitoring the weight changes as a function of time. The isothermal temperature was reached with the uncertainty in the time

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of ± 2 s and when reached it had a maximum initial fluctuation of 1.5°C. For each exposure time the result is the average of three determinations obtained by independent samplings of the same aged film.

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2.4. Other characterizations

Mechanical tests (tensile strength and elongation at break) have been performed on an Instron

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tensile testing machine 1115 at a traction rate of 500 mm min-1, at 25°C and 50% humidity. Gel-permeation chromatograms for the molecular weight determinations of iPP and LDPE

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were obtained in ortho-dichlorobenzene at 135°C. Infrared spectra were recorded on film by a Nicolet FT 20SXB instrument. IR spectra were collected in trasmission mode. Further information on the characterization of the polymers under examination is given in previous works [15-19].

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3. Results and discussion

3.1. Previous studies

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Results of previous works has shown that some important features of aged polyolefins change before new oxygenated groups are visible, both in thin films and in plates [15-19]. In particular, mechanical properties and molecular masses of thin films undergo changes that

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occur before oxygenated groups are observed. This can be better highlighted during natural aging in a temperate climate, ie with low thermal and light energy compared to the usual

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methods of accelerated aging which can flatten the differences between the various types of macromolecules and make more difficult the study of the initial period of degradation. The tensile strength of LDPE increases strongly in the first 2400 hours, while that of iPP starts to decrease from about 700 exposure hours. The elongation at break of iPP drops after approximately 700 exposure hours; in the case of LDPE this indicator increases slightly

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during its induction period of carbonyl groups. Furthermore, the average molecular weight Mw of LDPE increases in the first 2400 hours and then drops; on the contrary, the average

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molecular weight Mw of iPP decreases from the beginning of exposure. The mechanical properties of ethylene-octene copolymer films (AFFINITY), similar to LLDPE or VLDPE,

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decreases steadily in the first 2500 exposure hours. Based on previously published discussions [15-19] the time required for the formation of new carbonyl groups is summarized: about 2400 exposure hours for the LDPE film; about 800 exposure hours for iPP, regardless of the underlying thickness; about 500 exposure hours for AFFINITY films. IR data concerning carbonyl groups are shown in Table 1. Because in the first exposure period the crystallinity of LDPE and iPP thin films changes little, early changes in mechanical properties and molecular masses are an evidence in favor of reactions in the amorphous phase able to modify length and structure of the

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macromolecules, even before the formation of stable bonds with atmospheric oxygen. Based on these results, we investigated the reactivity of aged samples by thermogravimetry, using thin films to facilitate comparisons and to exclude the complications arising from the study of

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thicker materials [17].

3.2. Thermogravimetric curves

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The behavior of pristine and aged polyolefins during the thermogravimetric tests at 200° C is depicted in Fig. 1 which shows three characteristic parameters:

B = max weight increase, % C = time for the weight loss start, min.

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A = initial steady weight time, min.

Table 2 summarizes A, B and C values for the polyolefins under examination.

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The pristine iPP film maintains its own weight for 81 minutes (A = 81 min) when it is kept in air at 200° C in the thermobalance. After this time the sample begins to lose weight without

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going through an intermediate increase of weight. B = 0% for all the iPP samples, so A = C. Fig. 2 shows that the samples exposed in the range between 0 and 500 exposure hours exhibit

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in the thermobalance an initial steady weight time (A) inversely proportional to their environmental aging. Since in the analysis at 200° C all samples are in molten phase, the rapid decrease of the period of constant weight indicates that the environmental aging which precedes the formation of new carbonyl groups not only alters the morphology, but changes the structure of the macromolecules. After 500 exposure hours and up to about 1800 exposure hours, the time of steady weight (A) remains practically unchanged, thus indicating the achievement of a stationary phase in the degradation mechanism, before the accumulation of carbonyl groups increases even more the reactivity.

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During the isotherm test at 200° C the propylene polymer chains split up to generate volatile fragments, and then weight loss. This result is in agreement with the drastic decrease in Mn of iPP heated in air in the temperature range between 160 and 220° C [20]. The environmental exposure shortens the macromolecules even before the formation of new oxygenated groups

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[15]. On the basis of theoretical calculations, the typical reaction of the auto-oxidation mechanism, that is the formation of hydroperoxides starting from peroxidic radicals by extraction of an H• from the polyolefin (PH):

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ROO• + PH → ROOH + P•

is possible when the polymer has structural defects such as allyl or vinylidene double bonds

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[21]. In the case of iPP the β-scission is the main cause of formation of double bonds that allow the auto-oxidation. The clear change of the curve slope in Fig. 2 strongly supports the hypothesis that at least 500 hours of environmental aging are necessary to maximize the βscissions and thus facilitating the auto-oxidation mechanism. The iPP samples exposed more

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than 1800 hours lose weight even more rapidly into the thermobalance (Fig. 2), in accordance with the drastic decrease of tensile strength and molecular mass and with the achievement of the maximum absorbance values of the oxygenated groups [15]. That is, only a high

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concentration of carbonyl groups can increase the number of scissions by means of the Norrish reactions that occur during environmental exposure. The observations discussed

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above indicate that cleavage reactions preceding the oxygen incorporation play an essential role in changes due to exposure. Anyway fast thermogravimetric tests can effectively summarize the course of the iPP environmental degradation.

The thermogravimetric curves of the polyethylene samples are very different from those of the polypropylene tests. In fact the LDPE and AFFINITY samples during analysis at 200° C in air maintain a steady weight for an initial period, then increase progressively their weight up to a maximum value, return gradually to baseline and immediately after start to lose 8

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weight. The duration of the initial steady weight time (Figs. 3 and 4), the percentage of max weight increase (Figs. 5 and 6), and the time for the weight loss start with regard to the initial value (Table 2) depend on the hours of environmental exposure of the tested sample and the type of polyethylene.

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Thermo-gravimetric methods in literature have already revealed that, in the presence of oxygen, LDPE samples increase their weight before the scissions [22]. The intermediate weight gain was attributed to formation of oxygenated compounds which decompose

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subsequently [23]. Figs. 3, 4, 5 and 6 show that the beginning and the magnitude of the weight increase change strongly as a function of the polymer type and are influenced by the

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length of aging in the environment under relatively mild conditions. Therefore the environmental stress modifies the oxidisability and the overall reactivity of the macromolecules.

The total time lengths required to obtain the weight loss start (C) first undergo a reduction when the induction period for the formation of oxygenated groups is not finished (this is also

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true for iPP that, with regard to the scheme in Fig. 1, does not have the intermediate phase of weight gain). Afterwards a large number of carbonyl groups accelerates the fragmentation of

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the macromolecular chains due to effect of Norrish reactions of type I and II that occur during environmental exposure. Even the chain scissions of macro alkoxy radicals contribute to the

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decrease in molecular mass [24,25]. The exposure hours necessary to shorten the time for the weight loss start (C) in the thermobalance can be an induction time for degradation in general terms, alternative to that measured with IR which concerns specifically the firm incorporation of oxygen, for example in the form of carbonyl groups. Results suggest that macromolecular structures containing a high amount of tertiary carbon atoms favor the scissions and limit the highest weight increase (B) inside the thermobalance. So a null increase is obtained with all aged sample of iPP that has chains of carbon atoms of which 50% are tertiary. The aged ethylene-octene copolymers give values of maximum weight increases between 0.35%, for

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the more amorphous (probably the most branched) and 0.6% for the more crystalline (probably the most linear). In LDPE analysis the maximum weight increase reaches 1.6%. Also, for each polyethylenic structure, the highest weight increase is obtained with samples aged longer than the induction time for the formation of carbonyl groups. In other words,

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polyethylene samples that have incorporated a lot of oxygen during aging can not decompose quickly at 200°C without showing in advance, at the same temperature, high absorptions of oxygen. So the fragmentation of the polyethylenic chains requires absorption of oxygen in

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addition to the one already incorporated in oxygenated functional groups. The intermediate weight gain is also well visible in the thermogravimetric curves of very aged LDPE samples

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which contain insoluble and therefore cross-linked material. The absorption of oxygen in the thermobalance to form decomposable compounds, like peroxides, seems therefore possible when the aged polyolefin contains macromolecules of high molecular mass with structures partially branched and crosslinked, resistant to thermal cleavage.

It is possible that in environmental exposure conditions the solid polymer absorbs oxygen

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with formation of weak interactions, as in the case of the charge transfer complexes studied by Chien [26]. These complexes have been proposed as initiators of the UV degradation

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process of PP and PE [27,28]. When the available energy is high, the formation of carbonyl groups from peroxides and hydroperoxides derived from alkyl radicals is very fast. However

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there is a delay in the occurrence of oxygenated groups even during thermo-oxidations at high temperature [3,9]. In addition, under artificial aging conditions with fluorescent light at low temperature, which should promote the formation of peroxides, volatile peroxides in the gas phase were revealed after an induction period [4]. In the case of iPP, the strong tendency to β -scissions precludes samples absorbing more oxygen during the tests at 200° C, before losing light fractions. Therefore, the weight increases in the thermo-gravimetric measurements do not take place. The pristine LDPE films are characterized by significant amounts of double bonds that can favor the classic auto-oxidation mechanism, but also branching and

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crosslinking. Therefore the β -scissions are initially unimportant and can influence the degradation only at longer times. In fact the samples exposed for more than 6000 hours are characterized by a more rapid growth of the optical density of carbonyls and decrease of the weight-average molecular mass following the scissions [18,24], after the initial increase due

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to crosslinking or radical coupling reactions [29]. The lower reactivity of the polyethylenes explains the complexity of their thermogravimetric curves. Fig. 3 indicates that the initial baseline before any change in weight lasts 12 minutes

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for all LDPE samples aged up to 6000 hours. Samples aged for more than 6000 hours show a sudden and progressive decrease of the initial time to constant weight, preceding the weight

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increase. Also the increase in weight reaches the maximum value for the sample of LDPE aged for 6000 hours in the environment (Fig. 5). Table 2 shows fluctuating values for the C parameter of the LDPE samples, probably because scissions and oxygen absorption can occur simultaneously. This superimposition has been invoked for an LDPE film aged in air at 95°C

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[30]. However the net changes in A parameter, that is the initial period of steady weight at 200° C (Figs. 3 and 4), are useful to determine the sudden change of reactivity of polyethylenes exposed in the outside environment.

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Table 2 shows that the rate of decay in A parameter of the AFFINITY films is comparable to that of iPP films and is much higher than that of LDPE films. However, as already mentioned

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and unlike iPP, after this initial time the AFFINITY films increase its own weight, although with maximum values (B parameter) always lower than LDPE. In addition, the C parameter of the AFFINITY polymers, after an initial decrease, shows fluctuating values that resemble the behavior of LDPE. Similarly to LDPE, the absolute maxima in weight increases occur after the appearance of carbonyl groups. Therefore the set of thermo-gravimetric data reveals important details about the environmental degradability, in real conditions, of ethylene polymers similar to LLDPE that, especially with accelerated tests, are considered less susceptible to oxidation than LDPE [14]. Probably the presence of tertiary carbon atoms with

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short substituents (six carbon atoms) and the morphology characterized by low density and crystallinity, make these polymers more reactive in the overall process of environmental degradation. The increased resistance to photo- and thermal degradability of the most dense polyolefins has been attributed to the lower permeability to gases and to the lower number of

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tertiary carbon atoms [31]. Fig. 7 shows that the increase in density causes a decreased tendency to the scissions (increase of the C parameter) in the thermogravimetric tests of pristine polyethylenes. Maybe the structural characteristics that originate due to variations of

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the solid state density affect at least one of the processes involved in the environmental degradation in the early stages of exposure. It follows that the overall process of

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environmental degradation is the result of the reciprocal influences between chemical reactions and morphological variations. Accordingly, changes in the chain microstructure during distinct thermo- and photo-oxidation tests can give more precise information than the carbonyl index, at least in the initial stages of degradation [32]. The pristine LDPE sample contains a small amount of stabilizer [18]. On the contrary, the three AFFINITY copolymers

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do not show significant changes in the IR spectra after extraction with diethyl ether for 8 hours at boiling temperature [19], therefore they contain negligible amounts of stabilizers as

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traces of process antioxidants and are comparable with regard to the degree of initial purity. On the basis of these considerations, the stabilizers should not have an important role on the

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trend of Fig. 7. It is also likely that during the environmental exposure the stabilizers decrease and therefore lose progressively any importance in time differences for weight loss. The thermogravimetric curves allow to study in a simple and effective way the reactivity in the course of natural aging that includes phenomena of photo- and thermo-oxidation, in addition to several factors such as wind, rain and dust. Indeed, the determination of the three parameters (A, B and C) shows that the variations of oxidizability of polyolefins are not directly proportional to the carbonyl index of the aged samples and are accompanied by other alterations of the original material.

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The thermogravimetric method to analyze the reactivity of polyolefinic samples was applied to assess the spread of "infections" present in the materials, according to the aforementioned infective model [11,12]. For this purpose LDPE films containing different percentages of recycled polyethylene were compared. The films of this group are characterized by

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thermogravimetric curves according to the pattern in Fig. 1; their A and B parameters are shown in Tab. 3. The initial time with a constant weight, before the beginning of the oxygen absorption, is inversely proportional to the percentage of recycled polyethylene. The highest

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value (0.50%) of the B parameter is shown by the sample which contains exclusively recycled polyethylene, however this parameter is not directly proportional to the percentage of

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recycled polyethylene. These data confirm that the environmental aging changes the reactivity of the macromolecules which undergo permanent modifications, able to act as "infection points", regardless of the initial incorporation of oxygen. It follows a lack of linear correlation

4. Conclusions

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between the percentage of the recycled material and the path of degradation.

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The increase of reactivity of polyolefins exposed outdoors is detected at 200° C in air with variations in time required for the volatilization which may be preceded by increase of the

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initial weight, regardless of the presence of oxygenated compounds in the weathered samples. The maximum weight increase may be used to evaluate the degradation mechanisms. The comparison between TGA curves of polyolefins with different exposure times and/or initial structures allows for identification of the relative contributions of reactions that occur during environmental degradation, which include: oxidation, crosslinking and scissions. The reactivity of polyolefins aged outside in a temperate climate can be summarized, on the basis of TGA curves, as follows:

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iPP: degrades rapidly with cleavage reactions that precede the observation of any increase in carbonyl groups; the formation of carbonyl groups further accelerates the volatility; the starting material and the aged samples did not undergo weight increases in air at 200° C. LDPE: exposure slowly shortens the start of oxidation at high temperature, but produces

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materials capable of absorbing a large amount of oxygen at high temperature; also samples extensively aged and characterized by a high carbonyl index and crosslinks

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absorb oxygen at 200° C; exposure weakly affects the scission reactions. The reactivity of the recycled samples is higher than that of the original polyethylene and is able to

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destabilize the materials that contain them.

AFFINITY: exposure quickly shortens the start of oxidation at high temperature and influences the absorption of oxygen at high temperature; the tendency to scission is strongly affected by aging. The overall environmental reactivity is inversely

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proportional to the density of the pristine structure and is encompassed between iPP and LDPE. The increases in weight of the pristine and aged materials are lower than those of LDPE samples.

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Thermogravimetry is a method for evaluating the induction period of the reactivity increase and the general trend of degradation throughout the environmental aging. The advantage of

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this method is the description of polymer changes due to external exposure by thermogravimetric curves affected by all the possible causes of instability, even those that do not involve the incorporation of oxygen. In conclusion this procedure provides more information on outdoor aging than the usual measures concerning a single phenomenon, such as the onset of oxidation or modification of a property. It is also easier to point out the differences in degradability when comparing various polymers or even materials containing a recycled amount.

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LDPE. Polym Degrad Stab 1988;22:53-61. Saccani A, Toselli M, Pilati F. Improvement of the thermo-oxidative stability of lowdensity polyethylene films by organic-inorganic hybrid coatings. Polym Degrad Stab 2011;96:212-9. 31.

Ammala A, Bateman S, Dean K, Petinakis E, Sangwan P, Wong S, et al. An overview of degradable and biodegradable polyolefins. Progr Polym Sci 2011;36:1015-49.

17

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Gauthier E, Laycock B, Cuoq FJJ-M, Halley PJ, George KA. Correlation between chain microstructural changes and embrittlement of LLDPE-based films during photo- and

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thermo-oxidative degradation. Polym Degrad Stab 2013;98:425-35.

AC C

32.

18

ACCEPTED MANUSCRIPT FIGURE CAPTIONS

Fig. 1. Scheme of a typical thermogravimetric curve in air at 200°C showing three characteristic

increase (%); C = time for the weight loss start (min).

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parameters of pristine and aged polyolefins: A = initial steady weight time (min.); B = max weight

Fig. 2. Time for the weight loss start (C) of iPP films vs. outdoor exposure hours, in TGA curves.

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For all the iPP samples C = A (initial steady weight time).

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Fig. 3. Initial steady weight time (A) of LDPE films vs. outdoor exposure hours, in TGA curves.

Fig. 4. Initial steady weight time (A) of AFFINITY films vs. outdoor exposure hours, in TGA

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curves.

Fig. 5. Max weight increase (B) of LDPE films vs. outdoor exposure hours, in TGA curves.

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Fig. 6. Max weight increase (B) of AFFINITY films vs. outdoor exposure hours, in TGA curves.

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Fig. 7. Time for the weight loss start (C) of pristine polyethylene films vs. density, in TGA curves.

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Table 1. Time dependence of the carbonyl groups for iPP, LDPE and AFFINITY (PL1880, VP8770 and EG8150). LDPE optical densities at 1712 cm-1 relative to the absorption peak at 4321 cm-1

0.04

0.05

R = ratio between the area of the band in the range 1861-1669 cm-1 and that of the band in the range 825-640 cm-1 PL1880 VP8770 EG8150 0.00

0.00

0.00

456

0.05

0.06

0.04

720

0.08

0.08

0.15

0.10

0.18

0.18

0.19

0.19

1.22

1.50

1.50

1.60

1.68

1.80

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0

iPP absorbance at 1713 cm-1

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Exposure hours

912 0.05

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1008

0.11

1152

0.12

2112

0.18

2400 3000 3752 6000 8160 10320 10820 11040

0.10

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1776

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0.08

0.18 0.24

AC C

1368

0.53 0.49 0.42

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Table 2. A, B and C values, as from Fig. 1, for the polyolefins under examination.

PL1880

AFFINITY VP8770

AFFINITY EG8150 1

336

504

672

A = C, min.

81

21

8

3.5

3

Exposure hours

0

2000

6000

7080

A, min.

12

12

12

B, %

0.8

1.1

C, min.

61

Exposure hours

1368

1776

2112

2424

3

3

3.5

1

1

8160

8880

9600

10320

11040

11760

9

8

8

7

6

3.5

4

1.6

1.1

1.0

1.3

54

71

42

0

168

312

A, min.

34.5

11.5

2.5

B, %

0.2

0.4

C, min.

49

21.5

Exposure hours

0

168

A, min.

8.5

4.5

B, %

0.2

0.2

C, min.

20.5

16

Exposure hours

0

A, min.

7

B, %

0.25

C, min.

21.5

B = 0% for all the iPP samples.

1008

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168

0.9

456

720

912

1152

2.3

1.2

1.2

1.2

0.35

0.4

0.62

0.4

20

17.3

20.5

14

312

456

720

912

1152

2

1.8

1

1

1

0.1

0.2

0.3

0.45

0.4

14.5

12.5

10.5

14

13.5

168

312

456

720

912

1152

3752

1.8

1.5

1.3

1

1

1

0.5

0.1

0.18

0.22

0.35

0.28

0.2

8.5

14.5

11.5

13

10.5

7.5

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AFFINITY

0

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LDPE

Exposure hours

AC C

iPP1

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A = initial steady weight time (min.); B = max weight increase (%); C = time for the weight loss start (min.).

3752

3752

ACCEPTED MANUSCRIPT Table 3. Thermogravimetric data of LDPE films including a recycled amount. Max weight increase, % (B)

0

3.5

0.38

10

2.5

0.35

25

2.2

0.39

78

1.6

0.22

91

1.4

100

1.2

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Initial steady weight time, min (A)

0.36

0.50

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Recycled LDPE, %

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AC C

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AC C

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AC C

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AC C

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AC C

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AC C

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