Triboelectric series and electrostatic separation of some biopolymers

Accepted Manuscript Triboelectric series and electrostatic separation of some biopolymers Marian Żenkiewicz, Tomasz Żuk, Ewa Markiewicz

PII:

S0142-9418(15)00013-6

DOI:

10.1016/j.polymertesting.2015.01.009

Reference:

POTE 4370

To appear in:

Polymer Testing

Received Date: 9 December 2014 Accepted Date: 12 January 2015

Please cite this article as: M. Żenkiewicz, T. Żuk, E. Markiewicz, Triboelectric series and electrostatic separation of some biopolymers, Polymer Testing (2015), doi: 10.1016/j.polymertesting.2015.01.009. 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 Material Characterisation Marian Żenkiewicza,*), Tomasz Żukb), Ewa Markiewiczc) a)

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Department of Materials Engineering, Kazimierz Wielki University, 30 Chodkiewicza St., 85-064 Bydgoszcz, Poland, [email protected] b) Institute for Engineering of Polymer Materials and Dyes, 55 M. Skłodowska-Curie St., 87-100 Toruń, Poland, [email protected] c) Institute of Molecular Physics, Polish Academy of Sciences, 17 M. Smoluchowski St., 60-179 Poznań, Poland, [email protected]

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Triboelectric series and electrostatic separation of some biopolymers

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Abstract

Results of examination of order of positions in the triboelectric series of three biodegradable polymers, i.e., polylactide (PLA), polycaprolactone (PCL) and poly(3-hydroxybuterate-co-

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hydroksyvalerate) (PHBV) are presented. Results of electrostatic separation of binary mixtures of these polymers are also shown. The following order in the triboelectric series was

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found: (+)PHBV, PCL, PLA(–). Positions of these biopolymers in relation to some synthetic polymers were also determined. These results were confirmed by the results of measurements

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of dielectric constants of PLA, PCL and PHBV. The process of the electrostatic separation of the PLA/PCL mixture appeared to be entirely successful.

1. Introduction

The growing amount of polymeric waste worldwide is a negative effect of the increase in the manufacture of polymers. Disposal of that waste requires large landfill space while of the very slow decomposition of the polymeric waste causes significant contribution of that

*)

Corresponding author

ACCEPTED MANUSCRIPT waste to pollution of the natural environment. Effective management of the polymeric waste is a difficult task in respect of organization and technology [1,2]. This situation implies the necessity to develop various techniques for recycling of the polymeric waste, including mechanical recycling, that enables reuse of materials recovered from the waste. These

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techniques consist of many individual operations, segregation being one of the most important. This consists in isolating particular polymers from the waste after other impurities are removed [3,4].

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The necessity of segregation results mainly from the fact that most polymers are immiscible on a molecular level. This precludes the waste being mixtures of different

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polymers since products made of such mixtures exhibit too low mechanical strength, especially impact strength [5,6,7]. Therefore, thorough segregation is a necessary condition for proper management of the polymeric waste recovered by the process of mechanical recycling [8]. Electrostatic segregation, or electrostatic separation, is one of the methods for

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segregation of polymeric mixtures, including multicomponent mixtures containing the polymeric waste. Experience acquired so far confirms the usefulness, small environmental load and economic effectiveness of this method when applied to the mechanical recycling of

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waste containing commonly used polymers [8,9,10,11]. The electrostatic separation consists in suitable electrical charging of particles of a

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polymeric mixture and segregating them in the electrostatic field. Adequate electrical charging of the particles is of vital importance. Mechanical triboelectric charging and fluidized-bed triboelectric charging belong to basic methods for the electrical charging of polymers. The former technique is based on both the mutual friction of the mixture particles moving in a tribocharger and the friction of the particles against tribocharger walls [12,13,14,15], while the latter is a method in which friction between the particles occurs in a fluidized moving bed [16,17].

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ACCEPTED MANUSCRIPT During the triboelectric charging of binary mixtures, electric charges of opposite signs accumulate on the surfaces of the particles of different polymers. The charges appear due to transfer of electrons, ions and mass between these particles, as well as between the particles and the tribocharger walls [18,19,20]. Values and signs of the charges depend on the types of

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polymer and positions they occupy in the triboelectric series. The distance in this series between polymers of a pair of interest constitutes an important criterion for evaluating the possibility of electrical charging of these polymers and segregating them in the electrostatic

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separation process. The larger the distance in the series, the more effective is the electrical

dielectric constant [8,10,15,21,22,23].

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charging and separation. A positive electrostatic charge occurs on a polymer with a larger

Many results of the electrostatic separation of various polymeric mixtures and applied relevant devices have been reported in the literature. Binary mixtures, composed of commonly used polymers such as poly(methyl methacrylate) (PMMA), polycarbonate (PC),

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polyamide (PA), acrylonitrile/butadiene/styrene (ABS) terpolymer, polystyrene (PS), polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET) and poly(vinyl chloride) (PVC), were most frequently studied [14,16,24,25], although the possibility of two-

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stage separation of ternary mixtures such as ABS/PS/PVC were also examined [10]. Biopolymers belonging to the group of polyesters and polyester-urethanes, the

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production of which has grown rapidly in recent years, undergo biodegradation relatively easily under conditions of industrial composting, which is one of their important advantages. Thus, they constitute no serious environmental load [26,27,28,29]. However, this advantage limits interest in mechanical recycling of these polymers. Nevertheless, such polymers as polylactide (PLA) and polycaprolactone (PCL) can be multiprocessed with no essential deterioration of their physical properties, as follows from recent publications [30,31]. As a result, the mechanical recycling of waste from these polymers, and thus the electrostatic

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ACCEPTED MANUSCRIPT separation of them, may become profitable. However, there is no information in the available literature on the electrostatic separation of mixtures composed of biodegradable polymers like PLA, PCL and polyhydroxyalkanoates (PHA), as well as of mixtures of these polymers with commonly used traditional polymers.

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The purpose of the present work was to experimentally evaluate positions in the triboelectric series of three biodegradable polymers, PLA (which can be used not only in medicine and packaging industry but also in automotive applications [32]), PCL, and poly(3-

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hydroxybuterate-co-hydroksyvalerate) (PHBV). This is very important for determination of conditions for carrying out electrostatic separation of these polymers. Initial determination of

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the possibility of electrostatic separation of binary mixtures, PLA/PCL, PLA/PHBV and PCL/PHBV, was also the aim of this work. These biopolymers were chosen because they are of basic importance in the group of biodegradable polymers. In addition, PLA and PCL can be multiprocessed [30,31], which enables repeated use of waste of these polymers as products

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from mechanical recycling, and implies a necessity to thoroughly segregate mixtures of them. Densities of PLA, PCL, and PHBV are close to one another (1.16-1.27 g/cm3), which makes segregation of these polymers by standard methods very difficult. Therefore, electrostatic

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separation of mixtures of these polymers may be a practical and beneficial technique.

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2. Experimental

2.1. Materials

The following materials were used in the investigation: 1. Biodegradable polymers:

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ACCEPTED MANUSCRIPT a) Polylactide (PLA), type 2002D (NatureWorks®, USA), density (d) equal 1.27 g/cm3, containing 96.5 and 3.5% of monomeric units L and D, respectively. A structural formula of PLA is shown in Fig. 1.

structural formula of PCL is presented in Fig. 2.

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b) Poly(ε-caprolactone) (PCL), type Capa FB100 (Perstorp, Sweden), d = 1.16 g/cm3. A

c) Poly(3-hydroxybuterate-co-hydroksyvalerate) (PHBV), type SoGreen-2001a (Tianjin GreenBio Materials, China), d = 1.24 g/cm3. A structural formula of PHBV is shown

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in Fig. 3.

2. Synthetic polymers: poly(methyl methacrylate) (PMMA), type Altuglas HT 121

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(ARKEMA, Italy), d = 1.19 g/cm3; polycarbonate (PC), type Makrolon 2405 (Bayer, Germany), d = 1.20 g/cm3; polyamide (PA), type Ultramid B33 L (BASF, Germany), d = 1.15 g/cm3; and acrylonitrile/butadiene/styrene (ABS) terpolymer, type Terluran GP-35 (BASF, Germany), d = 1.20 g/cm3. The choice of these polymers was justified

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by the fact that their densities are similar to those of PLA, PCL, and PHBV. Thus, they cannot be separated from these biopolymers by standard methods, while their positions in the triboelectric series are favorable.

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3. Powder dyes: GREEN, BLUE, and RED (Evonik Colortrend B.V., The Netherlands).

2.2. Instruments

The following research instruments were used:

1. Laboratory drying oven, type SLW 53 (POL-EKO, Poland), intended for drying polymers that were used to prepare granulated materials meant for examination. 2. Co-rotating twin-screw extruder type BTSK 20/40D (Bühler, Switzerland), equipped with three automatically controlled screw feeders type VIP 6200 (INNO-PLAST, Germany), double-nozzle head provided with sensors of pressure and temperature of

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ACCEPTED MANUSCRIPT the plasticized material, conveyor belt provided with a set of fans to cool the extruded material, granulating device and vacuum pump was used to prepare and dye the studied granulated polymers. 3. Gas pycnometer type Ultrapycnometer 1000, model UPY-20 (Quantachrome

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Instruments, USA), used to measure densities of the extruded and granulated polymers. 4. Moisture balance, type MAX 50/1Do (Radwag, Poland), reading to ±1·10-4 g, provided with a drying chamber including a halogen lamp, meant for measuring moisture content

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in the extruded and granulated polymers.

5. Laboratory balance, type PS/600/C/2 (Radwag, Poland), of readability ±1 mg, used to

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weigh the studied samples and their fractions after electrostatic separation. 6. Prototype of an electrostatic drum-type separator, made at the Institute for Engineering of Polymer Materials and Dyes in Toruń (Poland), designed for segregation of the studied polymeric mixtures (Fig. 4).

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Basic structural units of this separator are as follows: a charging hopper (1), mechanical tribocharger (2), vibratory feeder (3), earthed cylindrical electrode (4), high-voltage elliptical electrode (5), slidable baffles (6), chambers for segregated materials (7) and

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high-voltage generator (8). Alternatively, the separator may be equipped with a fluidized-bed tribocharger, composed of a fluidizing chamber base with an air heater

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(9), exchangeable fluidizing chambers made of borosilicate glass (10), and a fan forcing air into the fluidized bed. This design of the separator enables various ways and conditions to be used for triboelectric charging.

7. Electrostatic meter, type Static Locator, model 983v2 (Meech, UK), intended for measurements of electrostatic potential of a charged polymeric mixture. 8. Single-screw extruder, type PlastiCorder, model PLV 151 (Brabender, Germany), the characteristic features of which are: e screw diameter of 19.5 mm, L/D ratio of 25, flat

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ACCEPTED MANUSCRIPT head with a nozzle of 170-mm width and with an adjustable gap size. The extruder was coupled to a calender consisting of three temperature-controlled rolls of 110 mmdiameter. The device was used to extrude a flat film, intended for measurements of the dielectric constant (εr) of the studied polymers.

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9. Broad-band impedance analyzer, type Alpha-A (Novocontrol GmbH, Germany), used for the measurements of the dielectric constant (εr) of the studied polymers.

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2.3. Methods

The sample preparation procedure included: (a) drying of the polymers intended for

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the investigation, (b) dyeing of PLA, PCL and PHBV and extruding all of the studied polymers in the form of granules, (c) conditioning of the granulated polymers, (d) measurement of density and moisture content of the conditioned granulated polymers, and (e) weighing of samples of binary mixtures meant for electrostatic separation. Samples were dried under the conditions specified by the polymer manufacturers,

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using the type SLW 53 laboratory drying oven with forced air circulation. The drying temperature of the particular polymers ranged from 50 to 120°C while the drying time was 6 h

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for all of the polymers.

Dyeing and extrusion of the polymers were performed in order to obtain polymeric

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granules of various colors and similar sizes and shapes. Because densities of the polymers differed very little, formation of granules of similar shapes and sizes was necessary in order to provide similar conditions for the electrostatic separation of individual mixtures. Various colors of the granules enabled identification of the polymers during separation. The dyeing and extrusion were carried out by using the type BTSK 20/40D twin extruder. The extrusion process was performed without outgassing, at a constant screw rotational speed of 250 min–1. Dyes in the form of granulated concentrates were added at 0.5 wt%. Polymers were poured into the extruder feed zone while taking care that the screws were not fully covered up. The 7

ACCEPTED MANUSCRIPT extruded material was cooled with eight fans placed over the belt conveyer. The granules were obtained in the form of cylinders of similar size (h ≈ 4 mm, r ≈ 2.7 mm). The granulated polymers were conditioned at 23ºC and 50.0% RH for 96 h, according to standard PN-EN ISO 291:2010. After conditioning, the measurements of density and

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moisture content of the particular polymers were carried out. The densities were determined by a type UPY-20 gas pycnometer, according to standard PN-EN ISO 1183-3:2003. Helium was used as the test gas, which could penetrate slits and pores of the sizes of 10-10 m. Prior to

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the measurements, the pycnometer was calibrated by using a calibrating sphere of known volume, while the samples were outgassed by purification in the pulsed mode. The

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purification cycle was repeated 30 times for every sample. The density results are given above in section 2.1. as characteristic data of each polymer.

Moisture contents of individual granulated polymers were determined with the use of the type MAX 50/1Do moisture balance. All the polymers were dried under the same

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conditions, including: (a) drying temperature, (b) drying profile, and (c) way of terminating the drying process. The drying temperature of 50ºC was assumed considering the lowest melting point exhibited by PCL (Tm ≈ 58-60ºC). The drying was continued until a change in

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the material mass was less than 1 mg in 60 s, when the drying process was automatically terminated. The moisture contents of all the granulated polymers were found to be less than

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0.2 wt%.

Considering the results of preliminary investigation of various polymeric mixtures,

fifteen binary polymeric mixtures were prepared for further examinations: (1) PLA/PCL, (2) PLA/PHBV, (3) PCL/PHBV (4) PLA/PMMA, (5) PLA/PC, (6) PLA/PA, (7) PLA/ABS, (8) PCL/PMMA, (9) PCL/PC, (10) PCL/PA, (11) PCL/ABS (12) PHBV/PMMA, (13) PHBV/PC, (14) PHBV/PA, and (15) PHBV/ABS. These mixtures were composed of equal contributions of the components (50 wt%). Ten samples of particular mixtures were weighed (200 g each).

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ACCEPTED MANUSCRIPT They were intended for treating with the electrostatic separator equipped with a fluidized-bed triboelectric charger with borosilicate glass walls (Fig. 4). The samples prepared this way were stored under standard conditions (T = 23ºC, RH = 50%). Taking into account earlier experiments [33,34,35] and the results of preliminary

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investigations, certain constant values of the separator parameters were assumed to be applied while determining positions of particular polymers in the triboelectric series. These values were as follows: (a) rotating speed of the earthed cylindrical electrode, 30 min–1, (b) vibration

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frequency of the vibratory feeder, 50 Hz, (c) voltage of the high-voltage elliptical electrode, 20 kV, and (d) interelectrode gap, 5 cm, which corresponded to average intensity of the

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electrostatic field in the interelectrode space of 4 kV/cm. It was also accepted that the electrical charging of particles of a studied mixture should attain a level that corresponds to electrostatic potential of at least 2 kV, which was to be measured in this investigation with the type 983v2 Static Locator electrostatic meter. At that level of electrical charging, the

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segregation process can properly proceed in the separator. In order to achieve this, the time of electrical charging in the fluidized-bed tribocharger had to be differentiated for different mixtures and was in the range 120-300 s. Attempts to separate biodegradable polymers were

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carried out at different values of rotational speed of the cylindrical electrode (15-30 min-1) and of voltage of the high-voltage elliptical electrode (10-22 kV). Application of these relatively

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wide ranges of the mentioned parameters was aimed at a more detailed study of this process. Flat films of PLA, PCL and PHBV were obtained by using the type PLV 151

PlastiCorder extruder. The thickness of the prepared films ranged from 150 to 160 µm. The samples were subjected to measurements of dielectric constant, which were performed with the type Alpha-A analyzer at ca 23ºC, within the frequency range of 0.01-1 MHz and at excitation voltage amplitude of 1 V. Prior to the measurements, gold electrodes (1 nm thick) were deposited on the samples by cathode sputtering in a type BALTEC SCD 050 vacuum

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ACCEPTED MANUSCRIPT coating machine. The measurement results were processed by WinDETA software. The values of εr were calculated from the determined values of sample capacitance, using the following relationship:

C ⋅ 4d ε 0 ⋅ π ⋅ D2

(1)

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εr =

Here, D is the electrode diameter, d, sample thickness, C, sample capacitance and ε0, permittivity of free space (8.854·10–12 F/m). The value of d was assumed as the arithmetic

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mean of the results of thickness measurements for ten samples. The effect of the electric field distortion on the periphery of the samples covered with the electrodes was also taken into

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account in the calculations [36]. The error resulted from that phenomenon was eliminated due to carrying out measurements while using several electrodes of different diameters. This procedure enabled determination of the permittivity corresponding to the electric field of a

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sample of infinite surface area.

3. Results and discussion

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3.1. Triboelectric series

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Signs of electrostatic charges of particular polymers in electrically charged binary mixtures that were further segregated by using the electrostatic separator shown in Fig. 4 are presented in Tables 1-3.

Signs “+” and “–” shown in these tables denote the positive and negative charges,

respectively, of the polymers, the symbols of which are given in the column headings. The charges occurred on triboelectric charging of these polymers when mixed with the particular polymers, the symbols of which are give in the row labels. The symbol “×” corresponds to mixtures of the same polymer, which were not examined. It follows from Table 1 that the

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ACCEPTED MANUSCRIPT order in the triboelectric series of the studied biodegradable polymers is (+) PHBV, PCL, PLA (–). The results shown in Table 2 indicate that the order in the triboelectric series of the studied synthetic polymers is (+) PMMA, PC, PA, ABS (–). This order generally agrees with

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the results reported in the literature. The published triboelectric series of various materials are very similar to one another. However, there are also differences [22] caused by different conditions of carrying out relevant experiments or by different additives introduced to the

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studied polymers by the manufacturer [37]. While limiting the analysis to nine commonly used polymers, independently of the results reported by Diaz and Felix-Navarro [22], one may

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present the following fragments of the triboelectric series of these polymers: (+) PMMA, PC, PA, ABS, PS, PE, PP, PET, PVC (–) [21]; (+) PMMA, PS, ABS, PC, PET, PE, PP, PVC (–) [15], and (+) PA, PMMA, ABS, PC, PET, PS, PE, PP, PVC (–) [23]. Two of them begin with PMMA, followed by PC, PA, and ABS or by PS, ABS, and PC. The remaining series contains

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also three of these polymers (PMMA, ABS, and PC) at the beginning, but they are preceded by PA. Thus, the above fragments of the triboelectric series are similar to one another to a great extent. The results obtained in the present work, shown in Table 2, conform to the data

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reported by Brück [21]. When the results presented in Tables 2 and 3 are combined, the following order in the triboelectric series of the studied polymers is obtained: (+) PMMA,

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PHBV, PC, PCL, PA, PLA, ABS (–). It must be mentioned, however, that during the triboelectric charging carried out in a standard separator, friction occurs not only between particles of polymers of a given pair, but also between polymer particles and tribocharger walls. This may be one of the reasons for differences between results published by various authors.

3.2. Dielectric constant

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ACCEPTED MANUSCRIPT The relative dielectric constant (εr) is an important property of a polymer that affects the triboelectric charging process. The measured εr values of the studied biodegradable polymers are shown in Fig. 5 and Table 4. As follows from Fig. 5, the εr values for PLA and PHBV depend to a small extent on the applied voltage frequency, whereas the value of εr for

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PCL increases considerably as the voltage frequency decreases below 100 Hz.

Several authors [38,39] concluded from the εr measurements that two relaxation processes occurred in PLA and PHBV: (i) the α process, connected with the glass transition,

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and (ii) the β process, associated with local oscillations of the polymeric main chain. They found that the α glass transition appeared in PLA and PHBV at temperatures ranging from 40

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to 120 and from –5 to 75°C, respectively, while the β transition, in the temperature ranges from 0 to 50 and from –115 to –20°C in PLA and PHBV, correspondingly. The results obtained in the present work (Fig. 5) indicate that both processes are reflected at ca. 23°C in a small increase in the εr values, occurring as the voltage frequency decreases below 1 Hz.

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PCL behaves slightly differently, revealing three types of relaxation: α, β, and additionally γ, the latter associated with oscillations of side groups of the polymeric chain,

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occurring at temperatures below 0°C [40,41]. Thus, the observed considerable increase in εr over the range of the lowest voltage frequencies at ca. 23°C (Fig. 5) is caused by direct

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current conductivity, which agrees with the results reported by Sabater i Serra et al. and Grimau et al. [40,41].

The most important conclusion drawn from the data shown in Fig. 5 is that the εr

values for the particular biodegradable polymers, measured at the voltage frequencies above 1 Hz, fulfill the inequality: εr(PHBV) > εr(PCL) > εr(PLA). The relative dielectric constants measured at the voltage frequencies of 50 and 1000 Hz are listed in Table 4. Thus, the εr values of PLA, PCL, and PHBV are arranged in a series consistent with the order of these polymers in the triboelectric series, determined in the present work. This 12

ACCEPTED MANUSCRIPT fact confirms validity of the results shown in Table 1. Difference in εr of two polymers electrically charged due to mutual friction significantly influences surface density of the generated electric charges and, thus, the process of their electrostatic separation. This density may be calculated from an empirical formula that takes into account differences in the relative

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dielectric constants of these polymers [42].

Different values of the dielectric constants of PLA, PCL and PHBV can be found in the literature [38,39,43,44]. These values for a given polymer produced on an industrial scale

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may vary because of different types and contents of additives introduced into that polymer by particular manufacturers. The other reason for the differences in εr may be significant if the

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phenomenon of the electric field distortion on the periphery of the samples covered with electrodes was not taken into account in the calculations (pt. 2.3). However, independently of these limitations, the εr value is an important indication used to evaluate the possibility of

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applying triboelectric charging to a given pair of polymers.

3.3. Electrostatic separation

Results of preliminary investigation of the electrostatic separation of mixtures of the

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studied biodegradable polymers are shown in Table 5. Only the purity of individual polymeric fractions obtained during the electrostatic

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separation process was used to estimate effectiveness of the segregation. The purity was defined as a quotient of the mass of a polymer included in the separated fraction and the mass of that fraction, expressed as percentage. As follows from Table 5, purities of the PLA and PCL fractions obtained due to segregation of the PLA/PCL mixture were very high (99.3 and 98.7%, respectively). Purities of the PLA and PCL fractions obtained due to segregation of the PLA/PHBV and PCL/PHBV mixtures were even higher (99.8 and 99.7%, respectively). On the other hand, purity of the

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ACCEPTED MANUSCRIPT PHBV fraction in both cases was insufficient since it equaled ca. 80%, which implies repeated segregation of this fraction.

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4. Summary

Triboelectric series of various materials published previously do not contain biodegradable polymers such as PLA, PCL and PHBV. The triboelectric series presented in

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the literature are similar to one another, but sometimes unexpected differences occur. They are caused not only by different conditions of carrying out examination, but also by

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differences in the content of various additives introduced to polymers by manufacturers of these materials.

Results of the present work indicate that PLA, PCL and PHBV are located in the triboelectric series close to its positive end, and are ordered in relation to some synthetic

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polymers as follows: (+) PMMA, PHBV, PC, PCL, PA, PLA, ABS (–). The order of PLA, PCL, and PHBV in the triboelectric series determined due to the triboelectric separation was verified by the results of measurements of dielectric constants of these polymers.

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Because PLA and PCL can be multiprocessed with no considerable deterioration of their functional qualities, the mechanical recycling of these polymers may be a beneficial

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alternative to composting. Thus, getting knowledge of the possibility of electrostatic separation of PLA and PCL is very important. The preliminary assessment of this issue made in the present work indicates, on the one hand, that the electrostatic separation of a PLA/PCL mixture provides fractions of these polymers of very high purity. On the other hand, effects of segregation of PLA/PHBV and PCL/PHBV mixtures were less good, because purities of the PHBV fractions in both cases were at a level of 80%, although the fractions of PLA and PCL were of high purity.

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ACCEPTED MANUSCRIPT In order to learn in more detail and improve the process of the electrostatic separation of PLA, PCL and PHBV when mixed with commonly used synthetic polymers, further investigation will be performed. Determination of suitable conditions for carrying out the

individual fractions, will be a subject of that investigation.

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26. R. Ukielski, F. Kondratowicz, D. Kotowski, Production, properties and trends in

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development of biodegradable polyesters with particular respect to aliphatic-aromatic copolymers, Polimery 58 (3) (2013) 167-176 (in Polish).

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27. J. Ganster, J. Erdmann, H-P. Fink, Biobased polymers, Polimery 58 (6) (2013) 423-434. 28. M.M. Reddy, S. Vivekanandhan, M. Misra, S.K. Bhatia, A. K. Mohanty, Biobased plastics and bionanocomposites: Current status and future opportunities, Progress in Polymer Science 38 (2013) 1653-1689. 29. J. Brzeska, P. Dacko, H. Janeczek, H. Janik, W. Sikorska, M. Rutkowska, M. Kowalczuk, Synthesis, properties and application of new (bio)degradable poliester urethanes, Polimery 59 (5) (2014) 365-371 (in Polish).

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1-9.

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Polish).

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blends with different ABS and PMMA contents, Polimery 59 (6) (2014) 495-504 (in

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ACCEPTED MANUSCRIPT 40. R. Sabater i Serra, J.L. Escobar Ivirico, J.M. Meseguer Duenas, A. Andrio Balado, J.L. Gómez Ribelles, M. Salmerón Sánchez, Dielectric relaxation spectrum of poly(ε-caprolactone) networks hydrophilized by copolymerization with 2-hydroxyethyl

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43. T. Nakatsuka, Polylactic acid-coated cables, Fujikura Technical Review (2011) 39-46 44. V.V.Meriakri, D.S. Kolenov, M.P. Parkhomenko, S. Zhou, N.A. Fedoseev, Dielectric properties of biocompatible and biodegradable polycaprolactone and polylactide and their nanocomposites in the millimeter wave band, American Journal of Materials Science 2 (6)

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(2012) 171-175.

19

ACCEPTED MANUSCRIPT Captions

Fig. 1. Structural formula of PLA.

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Fig. 2. Structural formula of PCL.

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Fig. 3. Structural formula of PHBV.

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Fig. 4. Prototype of electrostatic separator (for meaning of symbols, see text).

Fig. 5. Plots of the frequency (f) variation of relative dielectric constant (εr) for PLA, PCL,

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and PHBV at 23°C.

ACCEPTED MANUSCRIPT Tables

Table 1. Signs of electrostatic charges of biodegradable polymers PCL +

PHBV +

PCL

–

×

+

PHBV

–

–

×

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PLA ×

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Polymer PLA

Table 2. Signs of electrostatic charges of synthetic polymers PC –

PA –

ABS –

PC

+

×

–

–

PA

+

+

×

–

ABS

+

+

+

×

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PMMA ×

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Polymer PMMA

Table 3. Signs of electrostatic charges of studied polymers PLA × –

PHBV

–

PHBV +

PMMA +

PC +

PA +

ABS –

×

+

+

+

–

–

–

×

+

–

–

–

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PCL

PCL +

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Polymer PLA

Table 4. Relative dielectric constants (εr) of biodegradable polymers Polymer

Voltage frequency [Hz]

PLA

PCL

PHBV

50

2.2

2.9

3.3

1000

2.3

2.9

3.1

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Table 5. Maximum purity of polymeric fractions obtained during the electrostatic separation process PLA/PCL PLA PCL

PLA/PHBV PLA PHBV

Fraction purity [%]

99.3

99.8

80.4

99.7

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98.7

PCL/PHBV PCL PHBV

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Mixture Polymer

80.2

ACCEPTED MANUSCRIPT Fig. 1.

O O n

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SC

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CH3

ACCEPTED MANUSCRIPT Fig. 2. O O

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SC

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n

ACCEPTED MANUSCRIPT Fig. 3.

CH3

H3C

O

O

O

O m

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SC

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n

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AC C

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SC

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Fig. 4.

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Fig. 5.