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Freshly a lot awareness has been given to polymer nano composite particularly polymer layered silicate nano composite which perform intelligent [1]. Substitute to original filled polymer the principal function of food packaging is to sustain the condition and cover of food products during transportation and storage and to prolong their storage life by forbidding adverse situation spoilage microorganisms, chemical poisons oxygen, moisture, light etc. The food package should obstruct gain or loss of moisture, avoid microbial contaminations acts as a barrier against permeation of water vapours, oxygen, carbon dioxide and other volatile compounds have great mechanical strength, good thermal, chemical and dimensional stability, recyclability and biodegradability [2].

The thermo plastics are not non-totally recyclable and/or biodegradable, and hence produce dangerous ecological problems like white pollution [3]. Therefore options are highly applicable in specific PHB is a fully biodegradable and biocompatible polyester synthesized by bacterial fermentation from renewable sources such as cane sugar that has recently attracted much attention as an alternative to petroleum based polymeric material [4]. PHB is an isotactic linear thermoplastic built of 3 hydroxylbutyric acid with a chemical formula of [-O-CH-(CH3)-CH2-CO-]n. This biopolymer has already been applied in small disposable products and packaging materials [5]. To vanquish drawbacks such as high crystallinity (> 50%) low resistance to thermal degradation with a view to expand its range of practical application, new sound outs are desired like blending with other polymers [6,7]. Or filling with nanofillers such as organically modified montmorillonite (OMMT) [8].Multi-walled carbon nanotube (MWCNTS) [9].Nano-hydroxy a petite (HA) [10].Or layered silicates [11]. Improved mechanical performance and higher thermal and barrier properties have been obtained upon addition of small amount of nano-sized follows into this biopolymer matrix past fresh years (ZnO) nanostructures have become the attention of appreciable research because of it low cost easy usable, biocompatibility and chances of achieving surface modification with different functional group. They possess incomparable chemical and physical properties like deep ultraviolet absorption or antimicrobial activity in the PH range 7-8 even in the absence of light more over Zno universally used for applications such as optical devices [12, 13] and antimicrobial [14]. Zno demonstrate significant higher antimicrobial effect on staphylococcus aureus than other metal oxides like MgO, TiO2, Al2O3, CuO or CeO2 [15]. In addition, these nanostructures are considered to be non-taxicfreshly investigation have reported that ZnO do not cause any damage to DNA of human cell [16]. ZnO environmentally friendly nanomaterials possess exceptional mechanical properties low coefficient of thermal expansion and high thermal conductivity, thus are ideal to be used as reinforcing fillers in polymer composite. ZnO reinforced PHB homopolymer, which is the important objective of the current study. For such means raw ZnO nanoparticles at various loading have been assimilated in the PHB biopolymer matrix via sonication technique. An extended characterization has been carried out to interpret in detail the effect of inorganic nano-particle on the morphology, crystallization behavior, thermal stability, barrier antimicrobial and biodegradation of these novel bio nano composite that exhibit great capacity for food packaging application. The PHB content on modified particles, crystalline structure of ZnO nanoparticles were also studied along with anti microbial gas permeability and biodegradability activity. 

Probable Pathway of PHB/ZnOnanocomposite formation

PHB/ Znonanocomposites were prepared with ZnO contents of 1,3,5 and 7 with sonication process. The nomenclatures of samples at different parameters were tabulated in table- 1-

Table-1

Experimental Parameters for Synthesis of PHB/ Znonanocomposite

Sample Code	(HB) Mol dm-3	(K2S2O8) mol dm-3	(ZnO) Wt%	Ultrasound Watt/ KHz	% Conversion
PHB	3.033	1 x 10-2	0	0	88.9
PHB-1	3.033	1 x 10-2	1	0	87.8
PHB-2	3.033	1 x 10-2	3	0	82.8
PHB-3	3.033	1 x 10-2	5	0	80.8
PHB-4	3.033	1 x 10-2	7	0	70.2
PHB-2u1	3.033	1 x 10-2	2	120/80	79.2
PHB-2u2	3.033	1 x 10-2	2	120/60	81.2
PHB-2u3	3.033	1 x 10-2	2	80/80	75.85

 

Anti – Microbial Methodology-

The samples (PHB/ Zno) nano composite were dissolved in Dimethyl sulphoxide (DMSO) for anti- microbial bioassay Antimicrobial activity [19] was determined by Agar cup diffusion method against 4 bacterial pathogens (staphylococcusaureus, Bacillus, subtilis, Pseudomonas,aeruginosa, Escherichiacoli) and four  pathogenic fungi (candida albicans  candida KruseiTrychophytonmentagrophytes and candida viswanthii) . The test pathogens were obtained from institute of Microbial Technology (IMTECH) Chandigarh, India, Nutrient,Agar (NA) plates were inoculated with overnight culture of each bacterial suspension. Similarly for the fungal pathogens, potato Dextrose Agar (PDA) plates were inoculated with each funnel suspension. The plates with the inoculated organism were evenly spread out with sterile cotton swabs. Agar cups were prepared by scooping out the media with a sterile cork borer (10 mm diameter). The cups were then filed with 100 µl of the PHB/ Znonanocomposites that was dissolved in DMSO to get a concentration of 1 mg/ml. The plates were then incubated at 36 ±1⁰ C for 24 hours and 48 hours [20] for bacterial and fungal pathogens respectively.

Characterisation and Measurement Of Properties-

Characherisation-

The chemical composition of the intermediates and obtained particles was studied by Fourier transform infrared spectroscopy. FTIR using an FTIR spectrometer spectrum one (shimadzu IR Affinity-1) in the spectral range between 400 and 4000 cm^-1 with a spectral resolution of  4 cm^-1in transmittance mode  using  the KBR pellets technique.

Crystalline fractions of the synthesized powders were characterized by wide angle X-Ray diffraction (XRD) on an Expert prodiffractometer(Rigaku X- Ray machine) with a “Cu” anode as the X- Ray source, X- Ray diffractograms were measured at 25⁰ C in the 2$ range from 2 to 8⁰ with a step of 0.01 and step time of 1 second. The sample were loaded onto double-sided scotch tape, placed on a glass side and mounted on a quarter- circle EulerianCradle(Huber) on an XYZ stage. The X- ray beam was generated at 40 KV and 40 mA power and was collimated to about 800 µm spot size on the sample.  The incident w angle was1⁰. The XRD determinded the mean interlayer spacing of the ZnO and its PHB/ ZnO nano composite applying Bragg’s formula n ʎ=2sinɵ. The thermogravimetric Analysis (TGA) for the prepared samples were performed using a TGA apparatus model DTG-60 by shimadzu corporation, Japan. The samples were used under nitrogen purge and at a scan rate of/min to 800⁰ C. cm^-1

The transmission Electron microscope (TEM), Tec-nai 12, Philips, operating at 120 KV was used to study the dispersion of nanocomposite.

An ultra-cut low temperature sectioning system equipped with a diamond knife was used to cut ultra-thin specimens of 75 nm by cry ultramicrotome below. The glass transition temperatureof the sample. The specimens were transformed to a copper grid.

Gas permeability of the nanocomposites was measured with ASTM F 316-86 by susing oxygen permeation Analyzer (PMI) instrument model GP-20 I- ANY USA)

The anti – microbial activities of the prepared samples (PHB/ ZnO) nano composites were performed using 8 pathogens (4 Bacterial and 4 Fungi) and were determined by AGAR cup diffusion method. The plates where the bacterial activity was observed kept in an incubator at 36⁰ C for 24 hours.

The bio degradation of nano composite goes on decreasing with increase in time this is because of superior dispersion and interaction of the ZnO nanoparticles with the PHB matrix.

1. Polyhydoxybutyrate (PHB) monomer solution was used in this work was obtained from sigma- Aldrich chemic Gmbh company Germany which was used after purification. 2. Acidic solution of phosphoric acid (H3PO4). 3. Basic solution of sodium hydroxide (NaoH). 4. Zinc Oxide (Zno) nano powder (Aps- 240 nm Type-ii) was purchased from “ Sisco research lab pvt.ltd which is used as a nanofiller. 5. Initiator solution was potassium peroxydisulphate (Kps) from “Merck Specialties pvt ltd.” 6. Terminator solution was Ammonium Iron(II) sulphate from “ Merck specialties pvt. ltd. 7. N2(g) gas as an inert medium. 8. Ultrasonic cleaner (120 W/ 80 Khz) Emcolite. 9. Magnetic stirrer 2 MLH (REMI). 10. Hot air oven. Thermotec(TIC-4000) “ SecorScientificenggcorp”. 11. Electronic balance, Afconet (ER- 200A). 12. B.O.D. incubator, OS world (JRIC-10) 13. Bacterial Incubator B.T.L. ( 230 V, 1000W) 14. Laminar Air Flow Chamber Labotech B.D. instruments. 15. Auto clave steam sterilizer osworld (OAT) 239V, 3000W) All the chemicals used were of analytical grade and used as such. All the solutions were prepared using double distilled water. Polyhydroxy butyrate (PHB) ZnO non composite preparation:- METHOD- PHB/ZnO nanocomposite were prepared by sonication technique with varying Znoloading of 1%, 3%, 5% and 7% . The ultrasound waves of different powers and frequencies were used as 120/ 80, 120/60 and 80/80 KHz. Firstly, insita polymerization of PHB was carried out PHB of analytical grade was taken in a separating funnel to remove the stabilizers present in it through constant washing by acidic (H3PO4) solution followed by basic (NaOH) solution. The purified PHB was dispersed twice in double distilled water and 4 ml of washed PHB along with 14ml of distilled water was taken in a beaker and ultra-sonication for 20 mints [17]. Theinitiator KPS (Potassiumperoxydisuphate) 2 ml was also added to drive the reaction in a Nitrogen (N2) medium. The mixture was magnetic stirred at around 250 rpm under N2 gas at an ambient temperature of 〖650〗^0 C for 2 hours. During the time polymerization process was completed and white precipitate of PHB was detected. Then terminator solution ammonium iron (II) sulphate was added to the beaker to stop further polymerization. The precipitate was washed by distilled water in a filter paper and the filtrate was kept in a hot air oven at 〖70〗^0C to dry it out for 18 hours. The next day the residue was grinded to make it amorphous. Now, through this process of in- situ polymerization, ZnO nano particles was incorporated of various weights to the mixture of 4 ml washed PHB + 14 ml distilled water and prepared modified PHB with ZnO together to form polymer based nano composite. Similarly, 4 ml washed PHB along with of distilled water taken in a beaker and kept in aultrasonication for 20 mints. To make PHB 1% ZnO(by weight) 0.0322 gm of commercial ZnO nanoparticles was added to the solution followed by another round of sonication. The mixture was added with 2 ml of initiator KPS and kept on a magnetic stirrer for 3 hours with constant stirring and around 250 RPM under Nitrogen atmosphere. The white precipitate was observed after that another 2 ml of terminator solution added to stop further polymerization. The mixture was filtered by a filter paper and put to dry in a hot air over at 〖70〗^0. The residue was granted to modified PHB ZnO nano composite [18] in a power form. To add further another around of PHB + 3% ZnO (0.0966 gm) nano composite PHB+ 3 wt% ZnO ( 0.161 gm) and PHB + 7 % ZnO ( 0.2254 gm) polymer nano composite was synthesized. The whole process took 7 days to perform under optimum conditions and suitable temperature. The characterization and other properties were inspected thereafter.

Ftir Analysis -

Figure 01: FT-IR Spectra of PHB, ZnO and PHB+3% ZnO nanocomposite.

Figure (01) shows typical FT- IR spectra of pure PHB, nano- ZnO particles and then  ZnO particles modified with PHB. The loading was recorded in the range 4000-500cm^-1. All the FT-IR spectra, Figure (1) exhibit the PHB characteristic peaks   such as the strong stretching vibration of carbonyl groups (C-O stretching) at 2140cm^-1 . and the stretching vibration and bending vibration of methylene (CH2 bending) peaks at 2930 and 1453cm^-1 ., respectively. The peat at 1670 Cm^-1is due to the Oxidation of the as – received PHB in air, which results in the formation of carboxyl (C-O) groups. The peaks at 1251 and 1360 Cm^-1are assigned to the aliphatic -CH group vibrations of different modes in -CH and -CH2 respectively. When ZnO nano particles are incorporated into the PHB matrix the peaks at 1075, 1400 and 1450 cm^-1 are observed to become stronger and sharper which is due to the strong interaction between the PHB and the nanoparticles. This explains the phenomena that all of the PHB/ ZnO nanocomposite have stronger peaks at 1670 cm^-1 as compared to that of the pure PHB powders. Meanwhile, the peak at 2930 cm^-1is observed broader for nanocomposites. A strong stretching vibration of the hydroxyl group around 3500-3600 cm^-1 is due to the physically absorbed moistures in the polymer nanocomposites, especially for nano composites with 3%wt. particle loading. The ratio of peaks at 1453 and 1360 cm^-1 is observed to decrease and the peak at 2360 cm^-1 becames shaper when the particle loading reaches 3%wt. indicating a stronger particle – polymer interaction. It has been studied that an intense peak is found at 1670 Cm^-1 that corresponds to the stretching of ZnO bonds [22] on the other hand neat PHB displays a very strong band at 2140 cm^-1arising from the C=O stretching of the ester group [23]. The specter of the nanocomposites shows the characteristic peaks of both PHB and ZnO. The sample with 7%Wt. loading exhibits a broadening and up shift of the peak assigned to the hydroxyl stretching which appears at 2360 cm^-1such behavior has been attributed to the change from intra molecular to the change from intermolecular hydroxy1- hydroxyl interactions [24].

Analysis of TGA

Figure 02: TGA thermo gram of PHB, PHB +1%Zno, PHB +3%ZnO,    PHB +5%ZnO, PHB +7%ZnO nanocomposites.

Figure (02) shows the TGA curves of the pure PHB and PHB/ ZnO nanocomposites pure PHB is observed to degraded through two steps in air environment. The first step around 300⁰ C is due to the cyclization of the carbonyl groups into an extended conjugated ring system 41. This process is accompanied by degradative loss of H2, NH3 and HCN. In the second step more than 7%wt. PHB decomposes completely between 300⁰  and 600⁰  C. It is clearly observed that with loading of ZnO nanocomposite the thermal decomposition of material changes with temperature. In PHB 1% ZnO the thermal stability is near about the same but the 1^ststep degradation starts at higher temperature  than pure PHB that is 300⁰ c . But as the loading of ZnO nanoparticles increases with wt. % (1%, 3%, 5%, 7%) the thermal stability increases. The 1^ststepdegradate is higher at around 325-330⁰ c  and the 2^nd step the sample does not decompose completely and becomes stable at 600⁰ c . the wt% (7% weight left for 3% ZnO, 20 % wt. left over for 3% ZnO and 20% weight left over for 7% ZnO) left over increases with increasing in loading ZnO nano particles in PHB. So, it can be concluded that the thermal stability increases with increase of nanoparticles in polymer matrix.  Further, the PHB/ Nanocomposite prepared by in- situ polymerization process creates dispersion of Zno nanoparticles in PHB matrix by strong interfacial compatibility.  It has been studied that the bare nanoparticles exhibit a very small wt. loss (0.8 wt.%) below 300 ⁰Cprobably due to the removal of physically and chemically adsorbed water on their surface. Regarding the polymeric samples, neat PHB. PHB displays a single degradation stage that starts at  290 ⁰c and shows the maximum rate at around 33 ⁰c .The degradation occurs via random chain scission mechanism, producing shorter chain fragments with carboxyl terminal groups and with Crotonic acid as one of the characteristic by-products [25] It has been observed from the results that the incorporation of ZnO improves the heat resistance of PHB matrix ascribed to the barrier effect of the nano particles that effectively hindered the transport of decomposition products from the bulk of the matrix to the gas phase. Therefore, the high thermal conductivity of ZnO [26] should facilitate heat dissipation within the composite thus resulting in enhanced thermal stability.

XRD Analysis-

Figure 03: X-Ray Diffraction pattern of PHB, ZnO and PHB +1% ZnO , PHB +3% ZnO, PHB+5% ZnO and  PHB+7% ZnO nanocomposites.

The XRD patterns of pure PHB and PHB/ ZnO nanocomposites are shown in Figure (03). All the samples shows a sharp crystalline peak ( 17.3⁰) and a broad noncrystaline peak (22-30⁰) . PHB is unusual in that even atactic molecules  can crystallize. The characteristics peak at 17.corresponds to  orthorhombic PHB.(110) reflection, the XRD pattern of ZnO shows sharp crystalline peak  at 2⍬ 13⁰, 33.3⁰, 35.1⁰,36.4⁰, 47.7⁰, 56.7⁰,63⁰,67.5⁰, 70⁰ In addition, the diffraction peaks  at 2⍬, 31.3⁰,33.3⁰, 36.4⁰, 47.7⁰, 56.7⁰, 63.0⁰ , 66.5⁰ , 68.1⁰ , 70.0⁰ and 77.1⁰  , which became  notable with increasing Zno content,  , are assigned to the crystal graphic planes ofZnO (100), (002), (101), (102, (110), (103), (200), (112), (201) and (202) respectively However, the incorporation of ZnO  nanoparticles does produce peak  shift with  respect to  pure PHB. This revels that the PHB / ZnO nano composite exhibit a successful formation consisting of polymer and nano particle.[27, 28].In Fig (03) it was found that PHB/ ZnO nanocomposite, the peak corresponding to ZnO nanoparticle disappear after sonicated sample. This indicates that fully exfoliated structure [29] was obtained by the treatment of ultrasound. However the nanocomposite without treatment of ultrasound had XRD peak at lower 2⍬ angle than that of the ZnO nano particle. This indicates the intercalated structure of nano composite with less dispersion as compared to ultrasound sample. The interlayer distance for different intercalated nano composites were calculated by applying Bragg’s equation. It was observed that, there was a significant increase in the interlayer spacing (reduction in 2⍬ value) in PHB/ ZnO nanocomposites with increase of ZnO content. The strong interaction and compatibility of ZnO with PHB facilitates entrapment of PHB chain into the inter layer region of PHB resulting the intercalation and partial exfoliation of the ZnO layers in the PHB matrix. The higher crystallinity attained in ZnO reinforced PHB material is a key factor to enhance their mechanical performance on the other hand, in PHB ZnO nanofibers fabricated by an electrospinning method [30]. PHB has a crystallization peak temperature (Tc) of  76 ⁰C , which shifts to higher temperature in the presence of the nanoparticles. This increase is more pronounced at low ZnO loading (about 17 ⁰C  rise at only 1.0%wt) and becomes almost constant at higher concentra (≥ 5.0%wt), the maximum Tc increment being around 30⁰C  These result indicate that ZnO nano particles accelerate the crystallization of PHB due to heterogeneous nucleation effect further the crystallization peak sharpens in the nano composite demonstrating that these nano filler effectively act as nucleating agent and increase the overall crystallization rate of PHB.

TEM ANALYSIS -

Figure - 4

Team images were enrolled to further appraise the state of ZnO dispersion within the matrix and symbolic micrographs of the nano composite with the highest and the lowest loading are correlate in Fig (4) demographic analysis was achieved from the TEM images to obtained facts about the assessment of particle size and particle-distance in the nano composite and the results are also shown in Fig (4). In the sample worth 1.0 wt.%Zno (Fig 4a), the nano particles are evenly and well distributed, without forming agglomerates. They exhibit a narrow size distribution (Fig 4c) with diameters in the range of 40-100 nm and a mean value of 80 nm. Further the nano fillers [22] are fully regularly spaced showing an average particle-particle distance of 180 nm (Fig 4e). However, at 7 wt% loading (Fig 4b) the nano particle dispersion is less uniform compared to that of the sample with lower nano filler content. Thus the size distribution is broader (between size distribution is broader (between 40 and 150 nm) and the nano particle dimensions are larger, the mean diameter being 98 nm. Therefore the average inter particle distance (75 nm) significantly deceases resulting in increased propensity towards aggregation since the surface hydroxyl groups of ZnO have a strong trend to form hydrogen bonds among nano particles, hence flocculation of the nano filler can occurs, causing the formation of small clusters. Overall symbolic analysis confirms that the dispersion of Zno in PHB takes place as single particle at low concentration, while both as individual particles and small clusters at the highest loading studied. More essential, Zno dispersion within the biopolymer was achieved without the need for surfactants or coupling agent, making the fabrication process of nano composites easier, shorter and cheaper. The result involving the dispersal of Zno was supported by TEM micrographs of PHB ZnO loading of 7% for the samples obtained with and without sonication. The layer structure of untreated ZnO samples were ruptured by ultrasound treatment (Fig 4b). This implies that the polymer has entered into the interlayer spacing where individual Zno layers were being dispersed in PHB polymer matrix. The possibilities of dispersion may be due to complete exfoliation of ZnO under ultrasonic treatment.

]

Gas Permeability Properties-

Gas Permeability properties of PHB/ZnO nanocomposites

A precise edition in food packaging is that of migration and permeability so one of the important intentions when adding nano fillers (ZnO) [31, 32] to biopolymer matrix (PHB) is to develop their permeability properties to gases, vapours and organic compounds. Water vapours and oxygen are two important permeatantsstudied in packaging operation because they may transfer from the internal to external environment through the composite package wall result in a constant change in product respecting the oxygen permeability of the nano composite (Fig-5), a remarkable reduction is also observed as the ZnO content rises showing a margin (about 53% decrement as compared to that of pure PHB) at a precise concentration of 5% wt  this developed permeability achievement should be related to the homogeneous, ZnO dispersion causes strong interfacial adhesion with the matrix that causes chain immobilization combined its  increase in the degree of crystallinity of the matrix. Again it has been confirm that ZnO nanoparticle loading reduce the oxygen permeability of the polymer nano composite (PHB/ZnO) not only by formation of “tortuous” path but also via gas adsorption onto their surface. However the oxygen permeability of the nano composite with the highest loading is higher than that woth 5 wt%, ZnO, because nano filler (ZnO) aggregation starts to take place resulting in the formation of special path for the permeations to diffuse faster hence reduce permeability [33] presentation. It has been investigated that the incorporation of ZnO to PHB matrix has a positive effect on the gas permeability properties.

Figure -06

Figure 7: Zone Formation of PHB/ ZnO nanocomposites against test Pathogens.

Figure 8: Zone Formation of PHB/ ZnO nanocomposites against test Pathogens.

Figure 9: Zone Formation of PHB/ ZnO nanocomposites against test Pathogens.

Figure 10: Zone Formation of PHB/ ZnO nanocomposites against test Pathogens.

From the figure (6) and Table-2 we observe that PHB has got no antimicrobial activity against pathogens but ZnO do have antimicrobial activity. In almost all the cases with incorporation of ZnO with PHB the zones size increase. With higher percentage (%) of PHB / Nanocomposite the antimicrobial activity also increases but in case of Trichophytonmentagrophytes the Zone size increases to a certain threshold value, in this case (PHB + 5 % ZnO) and falls with higher percentage of ZnO nanoparticles. The prominent zones or size of zones are higher against Candida Krusei [21] which is a pathogenic Fungi.

Biodegradation

The biodegrading investigation is achieved using actuated sediment water. The biodegrading of Zno reinforced PHB nanocomposites  is examined with unpolluted PHB for a term of 180 days with a pause of 30 days the weight loss percentage for the composite along with unmixed PHB is determined and is compared in figure-11(a) & figure 11(b)  a decrease incline in percentage weight loss for the composite is renowned in comparison to pure PHB. Moreover, the bio- degradation of the nano composite goes on decreasing with increase in time this is because of superior dispersion and interaction of the ZnO nano particles with the PHB matrix. [34]

Residual mass percentage after degradation at different temperature along with Tg and Tm of PHB and PHB/ ZnO nanocomposite.

Sample  Residual mass percentage after    

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