Vol.:(0123456789)1 3

Journal of Packaging Technology and Research (2017) 1:165–180 https://doi.org/10.1007/s41783-017-0017-y

RESEARCH ARTICLE

Extrusion and Evaluation of Chitosan Assisted AgNPs Immobilized Film Derived from Waste Polyethylene Terephthalate for Food Packaging Applications

Amandeep Singh1 · Kamlesh Kumari2 · Patit Paban Kundu1,3

Received: 8 August 2017 / Accepted: 14 November 2017 / Published online: 28 November 2017 © Indian Institute of Packaging 2017

AbstractAntimicrobial Polyethylene terephthalate (PET) film was fabricated from PET waste by the process of 2° recycling, and then characterized and demonstrated at various environment conditions to evaluate its potential for for food packaging application. Blown PET film with thickness of 0.03 mm was extruded by simultaneous in situ extrusion of vPET and rPET in the ratio of 90:10. The obtained PET90:10 film was then impregnated in 3% chitosan solution under controlled pH in order to furnish a thin layer by pre-wetting phenomenon that works as a substrate for AgNPs immobilization. The immobilization of AgNPs over PET90:10 film was asserted by FESEM and EDX. Bactericidal property of film against Escherichia coli and Staphylococ-cus aureus are evaluated by disk diffusion assay method. Fabricated Ag-CC-PET90:10 blown film is proposed for the purpose of food packaging. The controlled migration of Ag from packaging film to food stuff is beneficial as it prevents microbial growth in packaged food stuff. The migration kinetics of Ag from Ag-CC-PET90:10 packaging film into packaged food stuff (food simulants), in terms of Ag content and the factors influencing the migration are also studied. Two food simulants; 40% EtOH and 4% HAc are used for migration study. Migration kinetics of Ag was studied for three ST; 10, 30, and 50 °C as well as for four St; 1, 24, 72 and 168 h. Results indicate that the maximum migrations of Ag in the alkaline and acidic food simulants are found to be 0.01812 and 0.07272 ppm respectively, at maximum ST and St. Migration of Ag content was found to be higher in acidic food simulant as compare to alkaline food simulant due to oxidative dissolution. The maximum Ag migrated content (50 °C, 168 h) was found under the permissible range prescribed by USFDA. The application of Ag-CC-PET90:10 blown film as food packaging material is itself an innovative and ecofriendly approach as post-consumption discarded PET waste can brought be up in utilization by means of 2° recycling.

* Patit Paban Kundu ppk923@yahoo.com

1 Advanced Polymer Laboratory, Department of Polymer Science and Technology, University ofCalcutta, Kolkata 700009, India

2 High Technology Laboratory, Department of Chemical Engineering, Sant Longowal Institute ofEngineering and Technology, Longowal 148806, India

3 Department of Chemical Engineering, Indian Institute of Technology, Roorkee 247667, India

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Graphical Abstract

Keywords PET · Secondary recycling · Antimicrobial · AgNPs migration · Food packaging

AbbreviationsEtOH EthanolHAc Acetic acidddH2O Double distilled waterPET Poly (ethylene terephthalate)vPET Virgin PETrPET Recycled PETPET90:10 vPET and rPET in 90:10 ratioAgNPs Silver nanoparticlesCC-PET90:10 Chitosan coated PET90:10Ag-CC-PET90:10 AgNPs immobilized chitosan coated

PET90:10 filmFE-SEM Field emission scanning electron

microscopyTEM Transmission electron microscopyEDX Energy dispersive X-ray spectroscopyST Storage temperatureSt Storage durationUSFDA United States Food and Drug

AdministrationEFSA European Food Safety Authorityppm Parts per millionsATR-FTIR Attenuated total reflectance fourier

transform infrared spectroscopy

Introduction

PET is a thermoplastic polymer and is widely in use for many end products like plastic films, food packaging, syn-thetic fibers, water bottles, wrappers, insulation materi-als, bottles/containers for soft drinks, alcoholic beverages, detergents, cosmetics, pharmaceutical products, edible oils etc. A major fraction of total PET is consumed by beverage industry itself to make bottles. Bottles are preferred over other containers for lots of reasons, for instances; durabil-ity, sealing easiness, aesthetic designs, reusability etc. The empty PET bottles discarded by the consumer after use is known as ‘PET waste’ or ‘post-consumer PET’. Recycling or reuse of PET waste becomes a need of hour as PET is one of the major material being introducing to environment rapidly. By keeping various aspects in mind, at present, the established methods of PET recycling are broadly divided into two methods—physical recycling and chemical recy-cling. Under physical methods, the PET wastes are reused to produce some plastic products with significantly inferior properties, whereas in chemical methods, the PET waste is put down into their respective monomers, which can further be used as raw materials to produce virgin plastic products. Physical method is a one of the way to hold the product ‘in

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use’ for maximum period of time. Since last decade, the recycling and modifications of post-consumer PET, being a valuable recyclable material, has gained keen attention as a source to obtain valuable products from them [1–7]. In recycling industry, PET waste bottles are set on a process—crushing, cutting, washing and drying to get ‘PET flakes’. PET flakes are further used as raw material for a variety of products such as polyester fibres, polyester sheet, strap-ping, or back into PET bottles [8]. APR (The Association of Postconsumer Plastic Recyclers) and NAPCOR (National Association for PET Container Resources) has claimed that United States observed 31.2% recycling rate for ‘PET pack-aging’ in 2013. Approximately 475 million pounds of recy-cled PET has been put forwarded for utilization out of 5764 million pounds of PET bottles [9].

Nanoparticle is a single unit or cluster of atoms in the size range of 1–100 nm or 10−9–10−7 m. Recently, nano-technology has been incorporated into food packaging industry. Nanocomposite packaging materials provides the desirable packaging properties by raising the enduringness to spoilable products [10–13]. Spoilage of food brings a great economic loss to any nation. Various antimicrobial based products and processes have been opted to prevent the food spoilage. Polymeric bioactive films containing nano sized antimicrobial agents have been found very effective for packaging applications. In ancient time, water tanks of seafaring ships were usually lined up with silver to keep water free from microbes [14–23]. Metallic nanoparticles especially AgNPs have been found as antimicrobial in many applications and their characteristic antimicrobial properties depend on size and shape; hence various combinations of size and shape of AgNPs have been found in wide appli-cations as a catalyst, optic sensor, antibacterial, data stor-age etc. [24–29]. It has been accounted that the antimicro-bial ability of AgNPs remains alive when incorporated in various materials, including polymers [30, 31]. AgNPs are well-known for wide-ranging antimicrobial activity against gram-positive and gram-negative bacteria, fungi and several viruses [32, 33]. It has already been reported that the size of metal NPs is inversely proportional to the degree of anti-microbial potential. Nano sized metallic particle has been reported as a good antimicrobial agent than their respective cluster form. It has also been investigated that antimicrobial

potential and/or toxicity of NPs is influenced by the concen-tration of NPs [34].

USFDA has framed several acceptable and tolerable limits for various migrants regarding food stuff packaging where rPET packaging remains in-contact with food stuff [35–40]. Since, food packaging is a sensitive stream due to health concerns, it needs proper fulfilling of parameters pre-scribed by various regulatory authorities. In conclusion, PET waste, being a non-biodegradable polymer, can be reused in packaging applications, especially for food packaging by the means of 2° recycling. The primary objective of this work is to utilize the PET waste so that it may retain ‘in-use’ for extended period of time. In sequence, the secondary objec-tive of this work is to incorporate antimicrobial property to CC-PET blown film in order to make it compatible as pack-aging material. In last, the assessment of Ag content migra-tion from packaging film to food stuff and its comparison with USFDA and European Food Safety Authority (EFSA) standards, is another objective of this research.

Materials and Instrumentations

Extruder Assembly

Single screw extruder (L/D ratio 28) with five temperature zones accomplished with assembly line was used to extrude the PET90:10 film. The extruder was placed horizontally. It consists of screw, barrel with heaters, gear box, 5 HP AC motor to drive the machine. Screw profile was designed as per the polymer being used (vPET and rPET). Extruder and its accessories are supplied by Extrumech Private Lim-ited, India. Foot mounting AC motor drives the extruder at 1440 rpm (revolutions per minute) as base shaft revo-lution. The temperature, pressure profile and screw speed while pelletizing and blow process are reported in Table 1. Ceramic heaters were inbuilt and capable to raise tempera-ture up to 600 °C. The extruder assembly is lined up as- extruder, chilled water sink connected with electric chiller, take up machine, cutter, bottle crusher, roll up machine, dehumidifier-cum-pre-heater.

Table 1 Temperature, pressure and screw speed for the pelletizing and blown film extrusion

Process Temperature (°C) RPM Pressure Material temp (°C)

Internal air flow speed

Barrel Gate Die

Z-1 Z-2 Z-3 Z-4 Z-5

Pelletizing 215 210 230 230 225 30 >30 MPa 225 NilBlown film 240 235 245 245 240 35 32–28 MPa 240 110 psi

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Reagents and Analytical Materials

The vPET (IV1 = 0.86 dl/g) in granule form was obtained as a gift from Dhunseri Petrochem, India. rPET granules (IV(see Footnote 1) = 0.80 dl/g) were pelletized by the extruder (2° recycling). Only transparent bottles are consid-ered as PET waste for this experiment. The chitosan used for wetting PET90:10 film was medium molecular weight chitosan (Mw—222 kDa, 98% Deacetylated) purchased from Sigma Aldrich (India) and was used as received. Sil-ver nitrate, acetic acid, sodium hydroxide, nitric acid, CaCl2 and CTSM (Sorbitol MacConkey agar with CefiximeTell-urite) were obtained from Sigma Aldrich India. Water solu-ble starch powder was purchased from Amrut International, India. Elvaloy® PTW containing 63, 31, and 6% (by weight) of ethylene, butyl acrylate and glycidyl methacrylate was obtained from DuPont, USA; ethanol was purchased from Merck India. Escherichia coli (gram negative, CECT 516) and Staphylococcus aureus (gram positive) were obtained from HiMedia India.

Extrusion of  PET90:10 Film

For hot melt EBM (Extrusion Blow Moulding) a single screw extruder was preheated to 330 °C melt temperature. Before starting the feeding for blown film purging was done by polyethylene pellets for 10 min and this procedure was done for each individual batch. PET90:10 film was fabricated by process, in which simultaneous in situ extrusion of vPET pellets and rPET pellets, in the ratio of 90:10 by mass and 1% (w/w of total batch) of Elvaloy® PTW as an impact mod-ifier, was carried out. The blend of PET and plasticizer was placed in the hopper and extruded to obtain a homogenous film with a thickness of 0.03 ± 0.002 mm. As the extrusion temperatures and screw speed for each process depends on the kind of extrudate, so the extruder parameters are opti-mized and then tabulated in Table 1. Prior to pelletizing, PET waste bottles were washed in 2N NaOH, followed by washing with double distilled water, dried and cut into small pieces by crusher. Uniformly cut pieces (flakes) were again rinsed and dried, and then kept in dryer-cum-dehumidifier, where flow of hot air has been provided over the flakes at 100 °C for 3 h and placed in desiccator for 6 h. Afterwards, flakes were subjected to pelletizing process in order to main-tain identical shape and size as vPET pellets had. Prior to in situ extrusion of vPET pellets and rPET pellets, they were kept into dryer-cum-dehumidifier at 100 °C for 30 min. From 1 kg of feed, about 11.1 m long film with 0.03 mm thick-ness (Ellipsometer, Nano Views SG/SM 1000) and 30 cm

width was drawn. Extruded film with above dimensions was weighted about 30 mg/cm2.

Physical Properties of Extruded PET Film

The crystalinity of PET90:10 film was evaluated by X-ray dif-fraction (XRD, Bruker D8 ADVANCE, with nickel filtered CuKα radiation, l = 1.54060 Å) measurements. A cut piece of the film with dimensions 4 mm × 4 mm was subjected to the instrument. XRD scans of the PET90:10 film were col-lected at 40 kV and 10 mA with 120 s exposure time.

To determine the dimensional stability of PET film the water absorption test and thickness swelling test, both were conducted as per ASTM D570-98. According to this standard samples with known thickness and weight, were immersed in ddH2O for 24 h at a temperature 25 °C. Before weighing and thickness measurement, specimens were oven-dried after the test at 100 °C for 6 h to obtain the oven dry mass and then moisture gain content was calculated with the help of following equation:

In above equation m2 and m1 are the oven-dry mass and the mass before the immersion test, respectively.

The dimensional stability of fabricated PET90:10 film was also evaluated against acidic medium as well as alkaline medium. As most of the food products are alkaline or acidic, hence packaging film is supposed to be withstand the pH of the food. Although, the PET is known as an inert polymer against mild acidic and alkaline solution, accordingly, the nature of fabricated PET90:10 film has been verified. A piece of known dimensions was kept into 0.1N NaOH solution and 3% acetic acid solution, separately. The piece of film then was analyzed by measuring its dimensions after 48 h. In addition to length and breadth, the thickness of the film was also measured and taken into account.

The physical–mechanical properties of PET90:10 film were determined utilizing Universal Testing Machine (Tinius Olsen 5KN) instrument with a head speed of 5 mm/min, and steady grip distance 100 mm. The standard and approved test method to determine the tensile properties of thin plas-tic film as prescribed by the American Society for Testing Materials (ASTM), method D638 was opted for PET90:10 film. Testing was carried out for four samples and then aver-age was taken with standard deviation.

Preparation of Silver AgNPs

In this work, 0.1 M AgNO3 and 8% (w/w) solution of sodium dodecyl sulphate (SDS) were used as metal salt precur-sor and stabilizing agent, respectively. Citrate of sodium solution (0.1 M) and NaOH were used as reducing agent.

(1)Moisture gain content % =(m2 − m1)

m1× 100

1 ASTM D4603, 60:40 of phenol and 1,1,2,2-tetrachloroethane

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Though, 0.1 M solution of citrate of sodium also works as a stabilizing agent at room temperature. The procedure to synthesize AgNPs is reported earlier by Guzmán et al. [53]. After completion of the reaction transparent colourless solu-tion of reaction mixture was converted to the characteristic pale yellow colour which further changed into pale red col-our. The appearance of pale red colour was indicated the for-mation of AgNPs. Further, the synthesized AgNPs were iso-lated by centrifugation. In order to remove excess Ag ions, the Ag colloids were washed gently with deionized water under nitrogen stream, and kept for freeze–drying. Thereaf-ter, a dried powder of nanosized AgNPs was obtained. EDX (Energy-dispersive X-ray spectroscopy, JEOL JSM-7600F, Japan) analysis of synthesized nanoparticles confirmed the presence of silver and no peaks of other impurity were detected. TEM (JEOL JSM-7600F, Japan) analysis for scal-ing the size and shape of AgNPs was carried out. Ultra Vio-let–Visible spectroscopy was executed during the reduction of AgNO3 to acknowledge the extent of reaction.

Functionalization of  PET90:10 Film by Chitosan Coating Followed by Immobilization of AgNPs onto CC‑PET90:10 Film

Chitosan is a linear polysaccharide consisting of 1,4-linked 2-amino-deoxy-β-d-glucan and found to be nontoxic, bio-degradable, bio functional and biocompatible in addition to having antimicrobial characteristics. Functionalization has been done by adsorbing a thin layer of chitosan over PET90:10 film in order to prepare a substrate for AgNPs immobiliza-tion. Chitosan solution (3% w/w) was prepared in double distilled water and the pH of solution was maintained less than 4 by the addition of dilute HCl solution. Thereafter, clean and dry PET90:10 film was immersed into the chitosan solution and placed on a platform shaker for 24 h. Later on, the film was dried at 60 °C in a vacuum oven to a con-stant weight, followed by drying in a dust free chamber at 40 °C for 3 h. It was reported that chitosan forms a thin layer at the water-plastic interfaces and the formation of interfacial layer of starch takes place by a process termed as pre-wetting [41]. Pre-wetting is expected to occur when chitosan is dissolved in a thermodynamically poor solvent (i.e. water). Therefore, formation of chitosan thin film onto

PET90:10 film surface leads to reduction in the interfacial tension. Abbreviations used for PET film, functionalized PET film and activated PET film are reported in Table 2. To confirm the successful functionalization of PET90:10 film by chitosan, a ATR-FTIR (Attenuated total reflectance Fourier transform infrared spectroscopy, Alpha E Bruker, Germany) was used to collect the spectra of the wave number, rang-ing from 500 to 4000 cm−1. When complete reduction of AgNO3 is confirmed after 24 h from beginning, some pieces of CC-PET90:10 film (50 mm × 20 cm) were immersed into the above reaction mixture followed by 10 ml addition of 1% acetic acid with constant stirring. Temperature of reac-tion mixture was maintained as 30 °C and reactor was kept in dark for 48 h. After 48 h, samples were washed with de-ionized water gently and dried by placing them in a vacuum oven (HIPL-028a, Hexatec, India) for 12 h.

Selection of Food Simulants

Two food simulants were taken for the study of AgNPs migration. One was taken as an alkaline simulant (EtOH 40%) and the other as an acidic simulant (HAc 4%). The selection of simulants to mimic the food stuff was made as described in the Directive 85/572/EEC by JRC (Joint Research Centre) European Commission in 2009 [42]. Moreover, the selection of food simulants depends on vari-ous factors like the material being tested, the food products for which the study is being carried out etc. All food prod-ucts are found either alkaline or acidic in nature; neutral foods are very few in number. Some examples for alkaline food products are dates, figs, kelp, limes, mango, pears, pineapple, raisins, vegetable juices, almonds, cherries, coco-nut (fresh), cucumbers, eggplant, honey, leeks, mushrooms, okra, onions, radishes, sea salt, spices, tomatoes etc. Like-wise, acidic foods may be enlisted as- beef, breads, brown sugar, cereals, chocolate, fish, molasses (sulphured), pasta (white), pastries and cake, pickles, pork, poultry, seafood etc. [43].

Instrumentation for Migration Tests

Migration of various elements from packaging material to food stuff can be tested mainly in four ways: either by using

Table 2 Abbreviations used for different films

Film notation Film constituents Process quotation

PET90:10 PET film fabricated by in situ extrusion of vPET pellets and rPET pellets (2° recycling) in the ratio of 90:10 by mass, followed by 1% (w/w of total batch) addition of Elvaloy® PTW

In-situ extrusion

CC-PET90:10 Chitosan coated PET90:10 blown film Functionalization of PET90:10 filmAg-CC-PET90:10 AgNPs immobilized CC-PET90:10 blown film Activation of CC-PET90:10 film

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a migration test cell, or by article filling, or by preparation of a pouch or by total immersion of article. As Ag-CC-PET90:10 film has sufficient seal strength to form durable pouches, single sided testing by pouch method was opted for this research. According to this method two pouches (total inner area 20 cm × 5 cm = 100 cm2) were taken and filled with 50 ml of each liquid food simulant (EtOH 40% and HAc 4%). In result of that, the surface to volume ratio in a pouch to be 2 cm2 for 1 ml of food simulant. The migration tests were carried out in accordance with the EU (European Unions) Regulation for plastic materials and articles intended to be in contact with food (Regulation 10/2011/EU). Neverthe-less, the total migration of Ag content must be below the permitted limit (0.05 mg Ag/kg food), in accordance with the EU Regulation (EFSA 2006) [44] and 0.22 mg/kg as per the USFDA [45]. The migrating amount of Ag content into food stuff is a sensitive issue as more than permissible level of Ag content may cause harm to human health.

The mathematical theory for diffusion in isotropic mate-rials states that the rate of transfer of diffusing substance through unit area of a section of the material is proportional to the concentration gradient at the solid–liquid interface as shown in following equation:

where, h is the coefficient of transfer by convection in the liquid next to the surface, CL,t is the concentration of the diffusing substance on the surface of the solid, Ceq is the concentration of the diffusing substance on this surface required to maintain equilibrium with the concentration of this substance in the liquid at time t [52].

To evaluate the Ag content in 1 ml of simulant sample, calcination was done at 600 °C in a muffle oven followed by an acid digestion of the ashes by HNO3. The resultant digestive is reduced in volume by excessive heating and then diluted to a final volume of 50 ml. Corresponding amount of Ag content was then measured for active surface of the packaging film (50 mm × 20 cm = 100 cm2). Determina-tion of 47Ag content was carried out by ICP–MS (Induc-tively Coupled Plasma—Mass Spectroscopy), assembled with NexION® 350D with dual-channel universal cell and

(2)−D(

dC

dx

)

= h(

CL,t − Ceq

)

dynamic reaction cell technology (Perkin Elmer, USA). Three replicates of each sample were analyzed.

Confirmation of Successful Adsorption of Chitosan Over PET90:10 Film was Ensured by XPS

The atomic composition of sample was measured after chi-tosan adsorption and then compared to the elemental chemi-cal composition of non-treated surface. For XPS analysis, samples were cut into 50 mm × 60 mm dimensions and subjected to XPS (K-Alpha™ Thermo Fisher Scientific Inc, USA, Al K micro-focused with vacuum system of 2 × 220 l/s turbo molecular pumps for entry and analysis chambers, auto-firing, 3 filaments with range of motion 100–4000 eV). The base pressure in the XPS analysis chamber was about 5 × 10−13 bar and the samples were excited with X-rays over a specific 400 µm area using monochromatic Al Kα1,2 radiations at 1486.6 eV. Since the samples were insulators, an additional electron gun was used to allow for surface neu-tralization during the measurements.

Fig. 1 XRD spectra of PET90:10 film

Table 3 Dimensions of PET90:10 film before and after immersion into the solutions

SD values are written in parentheses

Solutions At t = 0 h At t = 24 hLength: breadth: thickness: weight Length: breadth: thickness: weight

ddH2O 40 mm (0.01): 35 mm (0.01): 0.03 mm (0.01): 1.62 mg 40 mm (0.01): 35 mm (0.01): 0.03 mm (0.01): 1.63 mgMoisture gain content  % – 0.617%1 N NaOH 40 mm (0.01): 35 mm (0.02): 0.03 mm (0.01): NA 40 mm (0.01): 35 mm (0.02): 0.03 mm (0.01): NA3% Acetic acid 40 mm (0.02): 35 mm (0.02): 0.03 mm (0.01): NA 40 mm (0.02): 35 mm (0.02): 0.03 mm (0.01): NA

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Antimicrobial Assessment of Ag‑CC‑PET90:10 Film

Samples of PET film and Ag-CC-PET90:10 film were pre-pared in the form of disc of 8 mm in diameter for antimicro-bial activity assessment. Two specious of bacteria; Escheri-chia coli CECT 516 (gram negative) and Staphylococcus aureus (gram positive) were used for antimicrobial activity tests. The culture was diluted by sterile distilled water to 105–106 CFU/ml (Colony forming unit per milliliter). The resulting suspensions were swapped several times while

rotating the plate to ensure the uniform distribution using sterile cotton bud over the entire surface of culture plates containing CTSM agar. The film samples were placed on the surface of inoculated agar plate by using a sterile tweezers and gently pressed to ensure full contact to agar surface. The plates were then incubated at 37.5 °C for whole night, afterwards microbial zone and its surroundings were care-fully observed. Zones of inhibition were measured after 24 h of incubation at 35 °C. The comparative activity of discs containing PET and Ag-CC-PET90:10 were analyzed.

Fig. 2 Dimensional stability measurement set-up for PET90:10 film a 1N NaOH, t = 0 h, b 1N NaoH, t = 24 h, c 3% acetic acid, t = 0 h, and d 3% acetic acid, t = 24 h

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Sealing Unit

Ultra weld sealing machine manufactured and marketed by Crystal Electrodynamix Pune, India was used to seal the packaging pouches. This unit was situated at the last end of the production assembly line. Machine was mounted on the blown film line, vertically. Sealing machine consists of two pneumatic cylinders, sealing rods, toggle linkage, pistons, levers etc. While closing the sealing rods downward, the sealing action takes place as the prison got pinched itself by parallel sealing rods, subsequently opening of sealing rods provides time to toggle linkage for pulling next piece of film to be pouched. This mechanism goes repeated over again and again in automatic way, and pouches with desired properties without any serious defect were produced at take-away end of the sealing machine.

Statistical Procedures

The data were statistically analyzed using analysis of vari-ance (ANOVA) and linear regression analysis (Microsoft excel-2010).

Results and Discussions

Physical Properties of  PET90:10 Film

In current study, recycled PET is used as 10% (by mass) of the total mass of composition. After preparing the films of various compositions (vPET:rPET as 95:05, 90:10, 85:15, 80:20) they were tested for their mechanical properties e.g. tensile strength, Young’s modulus, elongation at break and F-5 values. By analyzing the mechanical tests result data (not mentioned in this paper) it was found that only PET95:05 and PET90:10 films could be used as packaging films. Further, out of these two, solo PET90:10 film was selected to carry out the current study, because it possesses more amount of rPET than precursor. PET90:10 film exhibits a typical diffraction pattern due to the crystalline nature of polyester. Crystal-lization peaks for sample is observed at 2θ ≈ 16.1°, 17.5°, and 22.6° corresponding to (0 1 0), (1 1 0), and (1 0 0) crys-tal planes, as shown in Fig. 1. The characteristic peaks of polyester have shown by the PET film which was fabricated from 90:10 ratio of virgin and recycled PET. The dimensions of PET film before and after immersion into ddH2O, 0.1N

Table 4 Physical properties of PET90:10 film

Stress to obtain 5% elongation is called F-5 value, SD values are written in parentheses

Properties Experiment value Standard Experiment conditions

Tensile strength 230 (6) N/mm2 ASTM-D638 Head speed 5 mm/min, 25 °C, 50% RHYoung’s Modulus 4500 (116) N/mm2 ASTM-D638 Head speed 5 mm/min, 25 °C, 50% RHElongation at break 98 (1)  % ASTM-D638 Head speed 5 mm/min, 25 °C, 50% RHF-5 value 105 (3) N/mm2 ASTM-D638 Head speed 5 mm/min, 25 °C, 50% RH

Fig. 3 FTIR spectrum of a PET90:10, and b CC-PET90:10

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NaOH solution and 3% acetic acid solution are quoted into Table 3. Water content absorbed by a known dimensions film was just 0.01 mg in 24 h, it represents that the mois-ture gain content percentage of PET90:10 film is found to be 0.617%, which facilitates the concept of utilization of this film in food packaging as far as water absorption is concern. Moreover, when film was kept immersed into 0.1N NaOH solution and 3% acetic acid solution, separately, neither the dimensions of the film were changed noticeably, nor the physical appearance of the film. It is clearly understand-able that the change in dimensional diameters and texture of the PET90:10 film were found negligible. It has been proved that the film is inert up to 24 h towards water, acidic and

basic solutions, chemically and physically both. In order to evaluate the dimensions of the film, simple academic scale is used having mm as smallest unit. The analysis of change in length, breadth and thickness of the film was carried out by a testing set-up as shown in Fig. 2. Physical properties of the PET90:10 were evaluated. The tensile strength, Young’s modulus, elongation at break and stress to obtain 5% elon-gation (F-5) tests were carried out as per the ASTM-D638 standard. Rectangle shaped (8 mm width × 50 mm length) pieces of film were taken for the test. Tensile strength of the film found to be 230 ± 6 N/mm2, whereas Young’s modulus was reported as 4500 ± 116 N/mm2. The value of Young’s modulus gives the information about change in the dimen-sion of film under tensile loads. In addition to above, the elongation of film at break was found 98%, whereas ‘stress to obtain 5% elongation’ (F-5 value) was found to be 105 N/mm2. All the physical–mechanical results about fabricated PET90:10 were found in the favor of film property for pack-aging applications. The physical–mechanical results are reported in Table 4.

Analysis of Functionalization of  PET90:10 Film by Chitosan

Figure 3 shows the FTIR spectrum for PET90:10 film (spec-tra-a) and CC-PET90:10 film (spectra-b). This analysis was carried out to confirm the tiny layer of chitosan adsorbed over PET90:10 film by means of pre-wetting phenomenon. The comparative analysis of both the spectrum leads to the fact that spectrum (b) exhibits additional characteristic peaks for chitosan. Characteristic FTIR peaks for PET were found at wave number of 3430, 1732, 1246, 1083 and 716 cm−1, for –OH, –C=O, –CHa

2, –CHb2 and –C–O–C, respectively

Fig. 4 XPS analysis of PET and CC-PET

Fig. 5 UV spectra during reduc-tion of AgNO3

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(spectra-a). The peak found at 2970  cm−1 correspond the oscillation/vibration of methylene group (–CH2–). In spectra-b, vibrational stretching for N–H, O–H, C–H, and C–O were found at 3233, 3190, 2878, 1090 and 1035 cm−1, respectively. Characteristic band at 3260 cm−1 was found due to symmetrical vibration of amine group. FTIR peaks for intermolecular bond stretching are found at 1550 and 1460 cm−1 for N–H, and C–H respectively. The additional peaks for chitosan in sample (b) confirm the presence of chitosan over the surface of CC-PET90:10 film. It has been undertaken from the result of FTIR that a tiny layer of

chitosan was adsorbed over CC-PET90:10 film, and further it was acted as substrate for AgNPs immobilization.

High resolution carbon spectra for the PET90:10 film and CC-PET90:10 film in the range of 280–296 eV is shown in Fig. 4. This analysis was executed to confirm the successful coating of chitosan over PET90:10 film. Characteristic peaks for carbon energy bonds in PET are observed at 285, 287 and 290 eV, for C–C, C–O and O–C=O, respectively. The CC-PET90:10 film exhibits an additional peak at 288 eV for C–N bond, which confirms the successful coating of chitosan over PET90:10. In the case of CC-PET90:10, due to insufficient dif-ference in bond energy for C–O and C–N bond, a single peak is observed at 288 eV.

Analysis of AgNPs Synthesis

Figure 5 shows the UV spectroscopic analysis that was car-ried out during the process of AgNO3 reduction to know the concentration of synthesized AgNPs. The band characteris-tics of AgNPs detected typical surface plasmon absorption maxima between 418 and 420 nm that strongly confirmed the formation of AgNPs. As the reaction time (reduction time of AgNO3) is increased, the intensity of the peak showed a gradual increment. This showed that the reduc-tion of the AgNO3 to Ag atoms was continued and resulted in an increase in the concentration of AgNPs. The successful synthesis of AgNPs by this route supported that the mixture of starch and NaOH acted as a good reducing as well as sta-bilizing agent. In order to carry out further analysis of syn-thesized AgNPs, obtained blackish colored mixture is dried in vacuum oven for 12 h. The size and shape of the AgNPs are examined by light scattering as well as by morphological

Fig. 6 Dynamic Light Scattering analysis of AgNPs

Fig. 7 a TEM image of AgNPs, b TEM image of AgNPs with dimentions

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analysis techniques. Figure 6 shows the DLS (Dynamic light scattering) results for particle size determination. From the figure, it is observed that the sizes of formed particles are in two ranges. Majority of AgNPs (> 80%) are in the range of 24–34 nm and the rest (< 20%) are in the range of 62–74 nm. Although, the opted route for AgNPs synthesis was uncon-trolled with respect to particle size, but obtained particles are in the desired range. The synthesized AgNPs are further immobilized onto chitosan without any sorting or sieving. In morphological point of view, the TEM analysis was carried out and the results are shown in Fig. 7. It is clearly visible in Fig. 5a that the synthesized nanoparticles are round in shape and are dispersed independently to each other, whereas,

Fig. 5b exhibits the size of particles. TEM analysis show that the sizes of the particles are of two ranges of 19.71–22.48, and 56–92 nm. Although, bigger sized particles are minors in count, hence no further sorting or sieving is done.

Analysis of Immobilization of AgNPs onto CC‑PET

FESEM (JEOL JSM-7600F, Japan) analysis has been car-ried out to examine the presence and dispersion of AgNPs onto CC-PET90:10 film. A small piece of film was cut for the FE-SEM (Field Emission Scanning Electron Micro-scope) analysis. Prior to putting the sample in the electron microscope, gold was sputter coated to make the sample

Fig. 8 SEM images of Ag-CC-PET90:10 showing the AgNPs dispersion. (White dots exhibit AgNPs)

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electro-conductive. Sputter coating for SEM is the process of applying an ultra-thin coating of electrically conducting metal such as Au (gold) onto a non-conducting specimen. Sputter coating prevents charging of the specimen which

would otherwise occur because of the accumulation of static electric fields. It also increases the amount of sec-ondary electrons that can be detected from the surface of the specimen in the SEM and therefore increases the signal to noise ratio. Fig. 8 shows the presence and dispersion of AgNPs over CC-PET90:10. Nano-sized AgNPs are clearly visible in white color in both the inset images. The elemental analysis of CC-PET90:10 film after immobilization of AgNPs (Ag-CC-PET90:10) was conducted to know the presence of 47Ag content (Fig. 9). Results obtained from EDX (JEOL JSM-7600F, Japan) characterization confirmed the presence of 6C, 7N, 8O, 47Ag, and 79Au. The carbon, nitrogen and oxygen were present in PET as well as in chitosan, whereas Au was detected due to gold sputter coating onto the sam-ple. The presence of 47Ag that came from AgNPs immobi-lization over CC-PET90:10 film, is confirmed by the EDX analysis. The output result stands in support to successful immobilization.

Fig. 9 Elemental analysis (EDX) for Ag-CC-PET90:10

Table 5 Total migrated amount of AgNPs from Ag-CC-PET film to food simulants in percentage, mg/cm2, and ppm

a Values are multiple of (10−6 mg/cm2)

Simulants ST (°C) St (hr) AgNPs migration% AgNPs migrationa ppm (± 0.00006)

Et-OH 40% 10 1 0.48 ± 0.02 0.96 ± 0.01 0.0019224 0.66 ± 0.02 1.31 ± 0.01 0.0026272 0.70 ± 0.02 1.39 ± 0.01 0.00278

168 0.83 ± 0.02 1.66 ± 0.01 0.0033230 1 1.80 ± 0.02 3.60 ± 0.01 0.0072

24 1.86 ± 0.02 3.71 ± 0.01 0.0074272 1.95 ± 0.02 3.90 ± 0.01 0.0078

168 2.37 ± 0.02 4.73 ± 0.01 0.0094650 1 4.12 ± 0.02 8.23 ± 0.01 0.01646

24 4.36 ± 0.02 8.71 ± 0.01 0.0174272 4.44 ± 0.02 8.88 ± 0.01 0.01776

168 4.53 ± 0.02 9.06 ± 0.01 0.01812HAc 4% 10 1 3.00 ± 0.02 6.01 ± 0.02 0.012

24 3.31 ± 0.02 6.61 ± 0.02 0.0132272 3.52 ± 0.02 7.03 ± 0.02 0.01406

168 4.17 ± 0.02 8.33 ± 0.02 0.0166630 1 5.18 ± 0.02 10.36 ± 0.02 0.02072

24 5.60 ± 0.02 11.21 ± 0.02 0.022472 6.01 ± 0.02 12.01 ± 0.02 0.02402

168 8.12 ± 0.02 16.23 ± 0.02 0.0324650 1 15.34 ± 0.03 30.67 ± 0.02 0.06134

24 15.66 ± 0.03 31.31 ± 0.02 0.0626272 16.50 ± 0.03 33.09 ± 0.02 0.066

168 18.18 ± 0.03 36.36 ± 0.02 0.07272

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Migration of AgNPs from Ag‑CC‑PET90:10 and Safety Assessment

According to Eq. (2) the change in the concentration of Ag in the Ag-CC-PET90:10 film with respect to the time is reduced as it diffuses into food stuff, continuously. The dif-fusion coefficient for Ag depends upon the coefficient of transfer of Ag-CC-PET film, the concentration of AgNPs on Ag-CC-PET90:10 film and concentration of AgNPs on sur-face required to maintain equilibrium. It has been postulated that packaged food stuff (food stimulants) does not possess any Ag content before being packaged, hence term Ce is not considered for this study. The migration kinetics of AgNPs from Ag-CC-PET90:10 film is studied by ICP-MS. 47Ag con-tent was calculated from the calcinated 1 ml of simulant sample at 600 °C in a muffle oven and then acid digestion

of ash is carried out with HNO3. Further, resulted residue is heated to reduce the volume and then diluted by double distilled water to a final volume of 50 ml. Corresponding amount of 47Ag content in above mentioned 50 ml solu-tion is measured for active surface of packaging film that has dimensions as 50 mm × 20 cm (one sided surface area 100 cm2) by ICP-MS. Migrated amount of AgNPs (10−6 mg/cm2) from Ag-CC-PET90:10 film into alkaline simu-lant (EtOH 40%) and acidic simulant (HAc 4%) at various ST and St is presented in Table 5. The AgNPs migration amount shown in table is multiple of 10−6 mg/cm2. The immobilized concentration of AgNPs was kept under the permitted range prescribed by USFDA. AgNPs loading for this experiment was kept constant as 200 × 10−6 mg/cm2 of film. Migration test is conducted at three different ST; 10, 30 and 50 °C as well as at four different St; 1 h, 1 day, 3 days and 7 days by keeping in mind the most possible conditions for most frequently used commodities. The maxi-mum AgNPs migration (9.06 × 10−6 mg/cm2) in 40% EtOH simulant is found at 50 °C and 168 h (7 days). The reason for high order of migrated amount of Ag can be explained according to Eq. 1. The increase in the concentration of the diffusing substance on the surface of the solid (CL,t) with increase in temperature and time, caused by the increment in kinetic movement of the NPs. It results in the migration of more number of AgNPs towards diffusing surface. As per Eq. 1 the migration of AgNPs from Ag-CC-PET90:10 to food simulants are directly proportional to the ST (storage tem-perature). The migration rate of AgNPs into acid simulant is found to be quite higher than that in alkaline simulant. It is due to the fact that after detaching from the Ag-CC-PET90:10 surfaces, AgNPs oxidative dissolution takes place at greater extent in acidic media. Whereas, in the alkaline medium, oxidative dissolution process takes place slowly as high pH suppresses the phenomenon. The oxidative dis-solution of AgNPs from Ag-CC-PET90:10 film for (HAc 4%) was found to be higher than EtOH 40% as a food simulant for same ST and St. Earlier reports asserted that the rate of release of Ag content decreased rapidly at pH values equal or greater than 8 [46, 47]. In current research, the mini-mum and maximum Ag content migrations are found to be 0.00192 and 0.07272 ppm respectively at different St and ST. (Refer Figs. 10, 11 and Table 5). These results indicate that they are in accordance with regulations of USFDA and EFSA. The applications of the nanotechnology brought a revolutionary change in applied areas of science and technol-ogy. As the food packaging is always taken as a serious issue for the safety point of view, so it’s very necessary to assess full and effective properties of NPs. The US Department of Agriculture, USFDA, Food Safety and Standards Authority of India (FSSAI), India, China Food and Drug Administra-tion (CFDA), Food Standards Agency, United Kingdom, EU etc. conduct assessment on NPs time to time for various food

Fig. 10 3D graph showing migrated amount of AgNPs from Ag-CC-PET90:10 film into a Alkaline simulant (EtOH 40%) and b Acidic simulant at various ST and St

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and food packaging industries in contrast to health safety. The relatively scarce and complicated scientific data about migration, exposure parameters, health concerns and toxici-ties facilitate the difficulties and problems in properly under-standing and utilization of various NPs [48].

Microbiological Analysis

Microbiological analysis was carried out to evaluate the anti-microbial potential of silver immobilized chitosan coated PET film (Ag-CC-PET90:10). The foils of Ag-CC-PET90:10 film along with reference PET film were tested in vitro with the standard ASTM (American Society for Testing and Measurements) method no. 2149-01. The antimicrobial test of the films are executed against Escherichia coli CECT 516 (gram negative) and Staphylococcus aureus (gram positive) as these two bacteria are commonly found in food and are responsible for food rancidity Both the strains were incu-bated at 37 °C for 24 h. From Fig. 12 a, b, it is clearly under-standable that the reference PET film (Ag content absent) has not shown any microbial inhibition zone; even it has promoted the growth of microorganism over itself. It may be so due to the contaminated surface of foil or hydrophobic nature of the film. The Ag-CC-PET90:10 film has shown suf-ficient microbial inhibition zones for E. coli and S. aureus both. It has been concluded from this analysis that fabri-cated Ag-CC-PET90:10 has sufficient antimicrobial potential to prevent antimicrobial growth. Since, PET film is nicely coated with chitosan, consequently very well immobilized by AgNPs while maintaining other properties in favor to packaging applications. The obtained results are in good agreement with the migration kinetics of AgNPs previously

discussed. However, the antimicrobial effect of AgNPs was more significant for E. coli (gram negative) than S. aureus (gram positive) at 37 °C after 24 h. These results are in accordance with previous accounted report that Ag nano-particles are more toxic to E. coli than S. aureus [49]. The reduced antibacterial activity of AgNPs for S. aureus is due to the difference in cell wall structure of gram positive cells and gram negative cells. The thick peptidoglycan layer of staphylococcal cell wall precludes the penetration of the NPs into the cytoplasm. Hence, the antimicrobial potential of NPs depends upon the penetration power towards cell wall and interaction chemistry with cytoplasm. After penetration through cell wall, the AgNPs react with thiol groups of the cell proteins and terminate the enzyme activity [50]. Another study claimed that Ag+ turned bacterial DNA into a con-densed form, leading to the death of microorganisms [51].

Conclusion

In this work, post-consumer PET waste is used as a par-tial constituent with vPET to fabricate the blown film with sufficient mechanical strength for packaging applications. Antimicrobial activity has been incorporated into ‘extruder blown film’ by immobilization of AgNPs onto chitosan coated PET film. Antimicrobial potential and migration pattern of Ag content from packaging film to food stuff have been investigated. Migration kinetics of AgNPs was studied for three ST; 10, 30, and 50 °C as well as for four St; 1, 24 (1 day), 72 (3 days) and 168 h (7 days). The maxi-mum migration of AgNPs, 18.18%, was found in 4% HAc food simulant for 168 h at 50 °C, whereas for 40% EtOH

Fig. 11 Obtained Ag migrated content compared with USFDA and EFSA regulations

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simulant, maximum migration was accounted as 4.53% at 168 h and 50 °C. It was observed that St, ST and pH of simu-lants directly influenced the migration kinetics of AgNPs which was supported by ICP–MS results. Migration of sil-ver content was found to be higher in acidic food simulant due to oxidative dissolution. The maximum migration of Ag in the alkaline and acidic food simulants were found to be 0.01812 and 0.07272 ppm respectively, at maximum ST and St, which are in-agreement of USFDA and EFSA. The bottom line of current research is PET waste can be uti-lized as minor constituent to fabricate blown packaging film,

and further, film can be coated with antimicrobial agents in order to impart antimicrobial potential. The mechanism of antimicrobial activity of film depends upon the migration/diffusion of Ag into food simulants, and it found in-accord-ance of USFDA and EFSA. Hence, Ag-CC-PET90:10 film can be brought into practice as an alternative that would be a sustainable approach to withhold PET waste into nature for extended time.

Acknowledgements This work is supported and financed by Min-istry of Food Processing Industries (MOFPI), Government of India.Remunerations to researcher is provided by Department of Science and Technology (DST), Government ofIndia under DST-INSPIRE scheme. Authors also acknowledged Dhunseri Petrochemicals India, for provid-ingvPET. The authors are also thankful to Indian Institute of Packaging (IIP) Kolkata to provide technical support.

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