Influence of nano-hydroxyapatite particles on the mechanical and antibacterial properties of polycarbonate films

In the present research, eco-friendly composite films of polycarbonate (PC)/nano-hydroxyapatite (nHAP) have been successfully prepared using the solution casting method with a concentration of (3, 5, 10 and 15% PS/PC with 1.6 nHAP). These films were characterized to investigate the influence of nano material upon the Ultraviolet (UV)-wethering of the mechanical properties employing tensile test, thermal properties utilizing Lee disk, and antibacterial properties utilizing culture method. From the tests, it was observed that the nano hydroxyapatite led to a reduction in the degradation and an increase in the thermal conductivity. The antibacterial studies manifested that the toxicity was severely decreased via the incorporation of nano hydroxyapatite and became highly antibacterial. Optical constants have been analyzed using UV–vis spectroscopy.Results reveal the decrease in band gap and enhancement in optical constants. FESEM images of 10% PS/PC and 10% PS/PC+1.6 nano particles exhibit a high degree of particle dispersion homogeneity within the 10% PS/PC matrix. The contact angle tests elucidated that the prepared films were highly hydrophobic with a hydrophobocity of 99%, which aids in the antibacterial capabilities and hence they can be used as packaging materials.

strength [14][15][16]. One of them is HAP (Ca 10 (PO 4 ) 6 (OH) 2 ), that exists in the mineral form of calcium (Ca) apatite in the nature. Such compound, which can be fabricated via chemical approaches, exists in tooth enamel, dentin layer, and bones. Also, it resists the organic and inorganic solvents, with exception for the acidic solvents [17,18]. It's also recognized that the nano-hydroxyapatite (nHAp) can work as inorganic transporter for the materials having a metal base in the food effective packaging. Thus, the hydroxyapatite (HAP) won't possess any bad influences upon the human health if employed for packaging the material because it's a natural bio-material [19,20]. The investigators have concentrated upon the production of the bio-degradable packaging materials containing hydroxyapatite (HAP) and on the study of their mechanical, and rheological, and thermal characteristics [21][22][23]. No investigation was found on employing the nHAP in the PS/PC film and its influences upon the performance of food packaging, particularly the UV-weathering. Demirel et al prepared polymer composites via solution casting method for milk bottle storage applications utilizing Polyethylene terephthalate (PET) and nHAP and studied the chemical, thermal, and mechanical properties, and the ultraviolet transmittance. It was found that the addition of nHAP in the vicinity of the polymer matrix has led to a decrease in the transparency and an increase in the UV absorption to a lower degree of less than 20% at a concentration of 0.8% nHAP compared to the 100% transparency of pure PET [24]. Zeng et al prepared nHAP/PVA composite using solution casting method for bone regeneration application. The authors characterized the composite using SEM, FTIR, XRD, and it was found that the composite surface is appropriate for the adhesion and proliferation of osteogenic cells. n-HA and PVA are in a homogenous dispersion if the n-HA content is <20 wt%. The contact angle results evinced that the addition of nHAP at 20% concentration to the PVA has led to a decrease in the hydrophilicity [25].
The present investigation aims to evince the nHAp influence on the properties of PS/PC film. Within such scope, PS/PC powder that contains nHAp has been utilized for producing packing containers. Also, the thermal conductivity, mechanical, and un-weathering, biological properties of the PS/PC/-nHAp composite films have been evaluated comprehensively.

Materials and methods
In the current investigation, hydroxyapatite with a purity of 97% and a size of 25 nm was purchased from Germany, Polycarbonate was purchased from Japan, and the Polystyrene was bought from America. Di-Chloro methane (DCM) (with a density of 1.325 gm cm −3 ) was obtained from Sigma Aldrich (USA). The two polymers (PS and PC) were dissolved in dicholoro methane; 7 grams from each polymer were dissolved in 100 ml of solvent. Polycarbonate (PC) was added to Polystyrene (PS) at different weight ratios (3, 5, 10, and 15 wt/%) to prepare PS/PC blends. Different amounts (0.8, 1.6, 3.2, 6.4 and 10 wt%) of nHAP were added to (Pure PS, Pure PC, and 10% PS/PC) to prepare PS/PC/-nHAP composite by casting method, and the solution was stirred continuously to obtain a homogeneous solution. These uniform solutions were then distributed upon a glass plate as well as permitted to evaporate the solvent gradually in air at the room temperature. The measured films thickness was (200 μm), using a micrometer placed at different places in each film to measure the film thickness, and an average reading was taken. The procedure to prepare the thin films is depicted in figure 1.

Characterization
The mechanical properties of PS/PC and the composite thick films were obtained via tensile tests employing a Universal Testing Machine (UTM) type UE3450 from Laryee Technology Co., Ltd., made in China. These films were cut into a dimension of (12 mm × 60 mm), and the thickness was measured via a digital micrometer having an accuracy of ±1 μm. The whole tensile tests were conducted at the room temperature (around 27°C), using a (5 mm min −1 ) cross-head speed for measuring the Stress-Strain curve, and the PS/PC/-nHAP films were tested. A famous standard process was utilized for determining the modulus of elasticity, maximum tensile strength, and elongation at the break. And, the prepared film was subjected to the weathering circumstances, like the ultraviolet radiation (UV) at various circumstances, employing (Accelerated weathering tester-QUV/spray-Q-LAB) the sample thickness was 200 microns and the area was 1 cm 2 . Temperature and moisture conditions (28C°, 50%). The agar diffusion test was also carried out against E. coli grown at the optimal temperature of 28°C. In a different way from the determined outcomes in the S. epidermidis existence, the haloes didn't change within the incubation time from (24 h) to (48 h); for such case, only the outcomes at the time of (48 h) were revealed. Furthermore, in the whole tests conducted in the E. coli existence, a dual halo was obviously observable, comprising an inner part, where these bacteria being nonexistence, enclosed via a circular crown of 'faint' microbial growth. The viability of cell was computed as the viable cells percentage in comparison with the unprocessed controls. Every outcome was the average viability standard deviation (SD) of three replicates. And, the value of probability (P) was regarded as the statistically non-significant variance among the outcomes [26,27]. The film is toxic when the compound-processed cells viability is (<70%) of the bad control, or when the death of cell death is (>30%) in accordance with the ISO standard (ISO 10993-5) to determine the in-vitro cytoxicity of medical apparatuses.
Water contact angles (WCAs) were measured utilizing the technique of Low Bond Axisymmetric Drop Shape Analysis (LBADSA), and the whole data of WCA were the mean of (7) measurements at various sites upon the surface. And, a drop of water was cautiously implemented upon the surface. Such procedure was observed via a CCD camera having a high speed with a setting of (35) frames/sec.

Results and discussion
4.1. UV-Weathering effect on the mechanical properties The influence of ultraviolet (UV)-weathering upon the mechanical properties of the prepared samples is depicted in the figures 2(a)-(f). This figure illustrates a reduction in the tensile strength with the time of weathering; which is ascribed to the degradation effect [26][27][28]. The harmful variations resulted from the ecologically created worsening include the discoloration, brittleness, chemical degradation, and impairment of mechanical properties. Certain small variations in the chemical nature of polymers may occur through the treating, and the highly important degradation takes place through exposing to the atmosphere of the service. The circumstances during the treating are comparatively harsh (for example, too much heat, and molecular shearing). Yet, the exposure to all of them was of a short period. Chemical changes, which may take place in a minor portion of the polymer molecules throughout the manufacture, cause the formation of sensitizing groups. Such undesirable intrinsic impurities, chemical structures, and a few of the supplemented ingredients are able to start or frequently speed up the deterioration through the application. The humidity, temperature variations and mechanical stresses are normally lesser in service atmosphere than through manufacture, but the exposure time is considerably longer. Additionally, a polymer has to absorb the energy of light, more precisely, the ultraviolet (UV) light. In polystyrene (PS) samples, the technical reduction was created via the technical degradation [29,30]. If PC is exposed to the UV-weathering in the presence of air, it experiences fast yellowing and slow embrittlement. Technically, the yellow discoloration is a significant opposing influence of polystyrene aging, for instant, through the outdoor exposure [31]. The main noticed reactions are the chain cross linking, the oxidation degradation and the bond session. Despite such great influences, the photo degradation mode of polystyrene is still the too controversial number of irregularities and impurities in the polystyrene, like the chain peroxide linkages, hydroperoxides aromatic carbonyl groups, and olefin bonds, which can be responsible for the photo beginning of the polystyrene radical oxidations [32,33]. The following fast oxidation carbonyl and hydroperoxide/groups resulted in a serious degrade and a loss of physical characteristics via the autocatalytic free radical mechanism [34]. The chemistry of degradation processes in PCs has been investigated widely through few previous decades; nevertheless, what occurring underneath the experiences is still under the debate, because the majority of such investigations were performed at various exposing circumstances. In the polycarbonate (PC), the chemistry that underlies the photo degradation has been characterized to (2) various mechanisms: Photo-fries re-arrangement and photo-oxidation (ring oxidations and side chain). It's proposed that through the start of the procedure of photo degradation, the reaction of photo-fries re-arrangement is the origin of released radicals. And, in the O 2 existence, the created radicals result in the products of photo-labile oxidation, like aromatic ketones and hydroperoxides. [35,36] Also, the hydroperoxides can start the fresh cycles of oxidation, resulting in autocatalytic photo oxidation. As well, the photo degradation created flaws in the polymer and dropped its mechanical characteristics [37]. However, through the long times of service, the majority of polymer products slowly lose their characteristics owing to the macro-molecular chain degradation.
Usually, polymers in their end-use condition aren't pure materials. And, in numerous situations, there're supplemented materials which vary the polymer's chemical engineering and/or engineering characteristics in an advantageous manner. Also, the polymer may include small monomer quantities, caught through the procedure of polymerization. Additives, like (nHAp) and impurities may contribute in the sluggish chemical degradation of polymer and, certainly, add the overall physical intricacy of polymer [38,39]. When the polymer is attacked via the atmosphere, the material performance into the service will be harmfully influenced. The performance degradation of polymer may result in early failure of material, causing an augmented downtime for the system, and demanding the expensive processes of maintenance [40,41]. However, even small variations in the compounding creation can cause substantial variations in the aging behavior of the (PC, PS, and 10% PS/PC)based material. It's well recognized that the polymer experiences (deacetylation) and photooxidative degradation created via the ultraviolet UV irradiation. And, as a result, the color of deacetylation polymer system will vary slowly from colored tuning to reddish brown; this was ascribed to the series of long-chain conjugated polymer [42,43]. Also, the following fast oxidation of functional groups was produced via severe degradation and the physical characteristics loss via the automatically released drastic mechanism [44,45]. Generally, the weathering slowly damages the majority of the mechanical properties of polymer. And, the first composition, morphology, reinforcement existence and type, morphology, and the service atmosphere nature obtain which mechanical properties will be influenced. And, the polymers' mechanical property that mostly subject to the deterioration is the elongation at break, which is regarded the highly meaningful indicator of weather ability [46][47][48][49][50][51]. The result of weathering effect on tensile strenght of the samples were shown in appendix in tables 1, 2 respectively and figure 3.    50 h). And, the experimental observed value of the PC and PS thermal conductivity is (0.20 W m .K −1 ) and (0.14 W m .K −1 ) at the room temperature, respectively. Also, it was obtained that the thermal conductivity increased by the reinforcement of (nHAP) [52]. In the amorphous polymers, such as (PC) and (PS), the thermal conductivity in the low-temperature zone (in the neighborhood of the room temperature) is governed via the phonon average free path variation. For (PC, PS, and 10% PS/PC), the phonon average released track is too minor due to the presence of many flaws in the amorphous condition at the room temperature [53,54]. Some flaws, like a bend in the chains, a gap between (2) chains, and the chains having a length that is smaller than the else, are generated in the system through the polymerization of polymers [55]. Thus, in the zone of temperature (from the room to the typical temperature), the active dependency of thermal conductivity is controlled [56,57] via the phonon average released track change owing to the phonon's structure scattering and the chain flaw scattering. After weathering, the films became further brittle in comparison with its initial characteristics. And, the word 'brittle' involves that there's no foreseeable plastic deformation in a material before the failure if it's exposed to a mechanical load. In the polymers that are deformable and tough prior to usage, the aging may result in a strain dropping to the failure, that's, it may result in a slow embrittlement. The embrittlement may be created via a diversity of parameters. Through the ecological aging, the molecular chain scission, the two main types of degradation, and the cross-linking, are the primary reasons of the embrittlement. Investigations evinced that the weathering makes the (PC, PS, and 10%PS/PC) and their based nano composites very brittle, as demonstrated via a noticeable decrease in the elongation to the failure and the strength [58]. Also, they manifested that the material in the exposing surface experiences a radical reduction in the molecular weight after a short weathering time as a consequence of the photooxidative molecular chain scission [59,60].

Cytotoxicity test
The highly critical state for a bio-degradable polymer to be used in the effective food packaging applications is its bio-compatibility in a certain atmosphere. And, the initial step in obtaining the bio-compatibility of suggested bio-materials is the testing of cytotoxicity [61]. The viability results of testing via the MTT assay of (HdFn   influence was predicted into the films. Also, the rate of the cell death is inside the satisfactory ISO standard range. As well, the results elucidated a smaller quantity of exposure to the film, better growth of cell, and normal proliferation. In other words, the growth and the cell endurance was contrariwise connected with the exposure  time. Additionally, the cytotoxicity test determined that the (PC, PS, and 10%PS/PC) are non-toxic, verifying that there was no significant toxicity upon the cell growth, and the investigations of the cell culture confirmed its bio-compatible nature and thus categorized it as a non-toxic polymer [64][65][66]. The nanoparticles addition like (HAP) is one method to enhance the (PC, PS, and 10%PS/PC) compatibility [56,58]. The all films were harmless materials because they depicted good percentages of viability (>90%). See figure 4. All th films were safe materials since they exhibited good viability percentages (higher than 90%) The Cytotoxicity of the samples were shown in appendix in tables 3, 4 respectively.

Antibacteria test
It can be noticed that the polystyrene (PS) manifested the enhanced transporter and the optical characteristics but had the low stiffness and tensile characteristics, which are significant factors for considering in the food packaging. Consequently, the film of 10% PS/PC with an optimum transporter, mechanical, and stiffness properties can be regarded as the highly appropriate film to be discovered for the uses of the food packaging. Therefore, the 10%PS/PC anti-microbial action was tested versus the two micro-organisms, viz., E. coli and S. aureus [67]. Figure 6 reveals the anti-microbial action of the films of (PC, PS, 10%PS/PC, PC+1.6 nHAP, PS +1.6 nHAP, and 10%PS/PC+1.6 nHAP). The all synthesized films displayed the antimicrobial action versus the test micro-organisms, and from figure 6 of the present investigation, it can be inferred that the inhibition regions for Staphylococcus aureus were lesser than those for Escherichia coli. Also, as it can be seen from this table 5, the inhibition region of the bacterial resistances has been considerably improved by the nano integration of HAP into PC, PS and 10%PS/PC film compared to pure (PC, PS, and10%PS/PC). As well, it was noted that the inhibition regions of the film of (10%PS/PC+1.6 nHAP) are closer to that of standard. This elevated microbial resistance is an important feature in obtaining the film usage in the food packaging [68][69][70]. Many resources elucidated that the nHAP has strong antibacterial capabilities. It is because of the nHAP positive charges that react with the negative charges of the bacteria cell membrane, also the nHAP can form reactive oxygen species (ROS) that inhibit the growth of bacteria resulting from the optical properties of nHAP that can capture visible light and generate hydroxyl radicals (OH). In this method, the disc agar method was used [71][72][73].

Contact angle
The hydrophilicity of film was obtained via measuring the contact angle of water. The contact angles of the contact of water for (PS, PC, 10%PS/PC, PS+1.6 nHAP, and PC+1.6 nHAP and 10%PS/PC+1.6 nHAP) are portrayed in figure 7. And, the polystyrene (PS) film possess the lowest surface wettability of the all induced films, with a (65.2°) contact angle, owing to its hydrophilic nature, where the low surface wettability results in a high contact angle, and vice versa [74,75]. Also, the contact angle of (PC, PC+1.6 nHAP, 10% PS/PC and 10% PS/PC+1.6 nHAP) and the (PS+1.6 nHAP) films of composite augmented radically to (82°, 99.2°, and 91.2°), correspondingly, owing to the (nHAP) phase existence, which is hydrophobic. As well, the hydrophobicity of produced films markedly enhanced as the (HAP) nanoparticle was added [76]. Such outcome is in agreement with the investigation of Costa et al [77]. The contact angles for the film are listed in table 6.

UV-Weathering effect on the optical properties
The absorption spectra of (PC+1.6 nHAP, PS+1.6 nHAP, 10% PS/PC +1.6 nHAP) film before and after the weathering process for different weathering times are illustrated in figure 8. It is noticed that the maximum wavelength is located at (275 nm) and it remains constant throughout the weathering process, while the absorbance increases after 10 h. And it will be decreased after 35 h. And, this is owing to the order of reactions produced via the incident lights, especially the UV waves, which result in the break of the highly vulnerable bonds, like C=C, C=O, and the formation of the radical that can oxidize in the O 2 presence [78,79]. As a result, such free radicals react with the O 2 and form peroxy radicals, which attack the polymer molecules on the surface. Also, the highly practical outcome is a notable absorbance spectrum in the UV zone. The variation of energy gap for the composite films after weathering is illustrated in figure 9. The variation of energy gap for the composite films after weathering is illustrated in figure 9. The band gap (Eg) of the PS/PC composite blend was shown to be increased by the incorporation of Nano-hydroxyapatite, this can be explained by reducing the size of the particle, where the values of the energy band gaps are ranged from 3.9 to 4.38 eV for PS100%, from 3.8 to 4.3 eV for PC100%, and from 3.95 to 4.4 eV for 10%PS/PC, and the absorption edge is shifted to higher energy (blue shift) with reducing the size of the particle. Regarding the blue shift of the absorption position from the bulk hydroxyapatite, the absorption onset of the current samples can be allocated to the straight electron transition in the Nano-hydroxyapatite crystals [80][81][82][83].

SEM analysis
The surfaces of blends underwent morphological SEM inspection. The results indicated that the PC was evenly and finely dispersed throughout the PS. Only one phase may be seen in the miscible phase area [84,85]. The final result exhibits that, from a morphological potential, the PC and PS are compatible. This is completely in line with the findings of mechanical testing. Nanoparticles were evenly distributed across a (10% PS/PC) composite film, as revealed in figure 10. In the (10%PS/PC) matrix, when the particles are distributed, there are no aggregation zones. The improvement in the tensile properties of film can be attributed to the scattering effectiveness of the nanoparticle filler (nHAP). Also, nHAP and 10%PC/PS were uniformly distributed if the nHAP content was no more than 1.6% nHAP [86,87].

Conclusion
In the present work, PS/PC with nano-hydroxyapatite composite films has been produced employing the casting technique. The nano-HAP influences upon the UV-weathering of the cast PS/PC thick films have been investigated. The mechanical,optical properties and thermal conductivity were improved by adding nano hydroxyapetite under the weathering effect. It was observed that the contact angle improved, and the polymeric film became water-repellent. It was concluded from the antibacterial test that all of the PS and PC/nHAp nano composites were highly compatible and biocompatible. None of the nano composites used in this study manifested the acytotoxic influence. The band gap (Eg) of the PS/PC composite blend was shown to be increased by the incorporation of nano hydroxyapatite . FESEM images of 10% PS/PC and 10% PS/PC+1.6 nano particles exhibit a high degree of particle dispersion homogeneity within the 10% PS/PC matrix. The film characteristic of PS/PC/nHAp will permit them to be utilized in different food packaging, comprising the dairy products, of which the visual appearance, taste, and odor worsen abruptly if they are subjected to the light.

Data availability statement
The data cannot be made publicly available upon publication because they are not available in a format that is sufficiently accessible or reusable by other researchers. The data that support the findings of this study are available upon reasonable request from the authors.
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The competing interests
The researchers have affirmed that that there are no competing interests present.

The funding
There is no fund has been taken for the present research investigation.

The contributions of authors
Nahida J Hameed and Evan T Salim conceived the introduced idea. Nahida J Hameed and Evan T Salim supervised the result of the present work. The researchers debated the outcomes and participated equally to the eventual research manuscript. Hadeel Abed conducted the experiments. The researchers offered crucial feedback and assisted form the investigation, analysis, and manuscript.

The conflict of interest
The researchers have affirmed that there is no conflict of interest.