Optical Properties Of Water Research Articles

Exploring the relationship between the optical properties of water and the quality and quantity of dissolved organic carbon in aquatic ecosystems: strong correlations do not always mean strong predictive power.

Optical absorbance and fluorescence spectroscopies have the potential to play an important role in monitoring aquatic ecosystems. This paper explores the relationship between the optical absorption and fluorescence characteristics of water samples taken from 18 sites (spanning a range of aquatic environments including lowland rivers, small and large dams, and floodplain wetlands) with their dissolved organic carbon (DOC) concentration and 28 days bioavailability Both optical absorbance in the ultraviolet region and fluorescence above excitation wavelengths of about 240 nm and emission wavelengths above about 350 were correlated with DOC concentration (r(2) > 0.8). The initial (pre-incubation) optical absorbance in the UV region (r(2) ≈ 0.7-0.8) and fluorescence attributed to both 'humic like' (r(2) = 0.84) and 'tryptophan-like' (r(2) = 0.87) fluorophores correlated with DOC bioavailability. These correlations were used to develop empirical linear models relating the initial optical properties of water with DOC quantity and quality. The robustness of these models was then tested against a second suite of water samples from 12 different sites, collected independently of those used in the model development. Although based on strong correlations, the empirical models were not particularly good at predicting the bioavailability of DOC in the model validation samples. We suggest that one of the reasons for the low predictive power of the models is that the strong correlations observed between DOC bioavailability and optical absorbance in the UV region or fluorescence and are co-incidental rather than causal. Changes in UV-absorbance or fluorescence during the incubation experiments are not consistent with changes in DOC concentration. One of the best predictors of DOC bioavailability is the initial concentration of DOC. We argue the strong correlation between DOC bioavailability and initial fluorescence intensity or UV absorption simply reflects the strong correlation between initial DOC concentration and initial fluorescence intensity or UV absorption. We argue that unless there is an underlying causal relationship between two components (the component of interest and a surrogate measure for that component) care should be taken in extrapolating correlative models beyond the data set used to create them.

Deriving inherent optical properties from background color and underwater image enhancement

The colors and quality of images acquired in underwater conditions can be very poor due to the specific propagation properties of light in water, and this degradation effect is relative to the optical properties of water. We find that the background color of underwater images has a relationship with the inherent optical properties of water medium. In this paper, we propose a method of deriving inherent optical properties of water from the background color of underwater images based on an underwater image formation model. Simulations and image enhancement results show that the proposed method can effectively estimate inherent optical properties and can be used for underwater image enhancement with good performance.

Influence of Field Environmental Factors on Water Transparency

Water transparency is an important parameter describing water optical property. Based on the summarized research results in recent decades, this paper systematically expounded the mechanism of various influencing factors for water transparency in the field environment, and classified the factors into three categories: direct influencing factors (including suspended solids, CDOM and algae), distinct indirect influencing factors (including nutrient concentrations and aquatic plants), and weak indirect influencing factors (including temperature, pH). In different water bodies the contribution impacts of direct influencing factors vary with the different environmental characteristics. Distinct indirect influencing factors usually have composite effects on water transparency, which make the mechanism more complex. Weak indirect influencing factors are constrained by other environmental factors, featuring more uncertainty. According to the analysis of previous researches, the following three aspects should be concerned in further studies: (1) more mechanism researches should be conducted based on field measured data analysis; (2) coupling mechanism of multi-factor for water transparency should be concerned.

Specific inherent optical properties of highly turbid productive water for retrieval of water quality after optical classification

Assessments of specific inherent optical properties (SIOPs) and their variability in highly turbid and productive inland waters are essential for the accurate estimation of water quality. A new optical classification method including two classification criteria [i.e., normalized remote sensing reflectance slope (NS), and normalized remote sensing reflectance depth (ND)] was developed to divide remote sensing reflectance into four classes, i.e., class 1 (NS 0.21) is low turbid and high productive water; class 3 (NS > −0.0017 and ND −0.0017 and ND > 0.009) is high turbid and high productive water. The relationships between phytoplankton absorption at 440 nm [a ph(440)] and chlorophyll-a concentration [C chla] as well as between particle backscattering coefficient at 440 nm [b bp(440)] and total suspended matter concentration (C TSM) after classification were obtained from a large number of in situ data in Lake Taihu. The measured specific phytoplankton absorption $$[ {a_{\text{ph}}^{*} \left( \lambda \right)} ]$$ and particle backscattering coefficient $$[ {b_{\text{bp}}^{*} \left( \lambda \right)} ]$$ show significant variations even within the same class. The mean values of $$a_{\text{ph}}^{*} \left( \lambda \right)$$ at 440 nm $$[ {a_{\text{ph}}^{*} \left( {440} \right)} ]$$ for each class are 0.048 ± 0.013, 0.060 ± 0.012, 0.083 ± 0.021, and 0.056 ± 0.017 m2/mg, respectively. The mean values of $$b_{\text{bp}}^{*} \left( \lambda \right)$$ at 440 nm $$[ {b_{\text{bp}}^{*} \left( {440} \right)} ]$$ for each class are 0.035 ± 0.01, 0.024 ± 0.004, 0.041 ± 0.009, and 0.038 ± 0.009 m2/g, respectively. The power functions of SIOPs and water constituents’ concentration indicate that $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ vary with C chla and C TSM. The validation results show that our proposed values for $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ cover a very wide range of water optical properties, which are characterized from clear water to highly turbid productive water. The validation results also suggest that the retrieval accuracy of C chla and C TSM bio-optical model was improved after classification. The root mean square error (RMSE) of C chla was improved from 14.18 to 7.43 μg/L (mean value of all classes) and RMSE of C TSM was improved from 32.98 to 26.10 mg/L (mean value of all classes). Thus, the temporal and spatial variation of $$a_{\text{ph}}^{*} \left( {440} \right)$$ and $$b_{\text{bp}}^{*} \left( {440} \right)$$ should be considered in the bio-optical retrieval model of water quality. In complex optical properties of inland water, retrieving the water constituents with high accuracy needs to classify the water optical properties from the remote sensing spectrum by optical classification method. The figure shows the water color examples of each class .

Optical Closure of Apparent Optical Properties in Coastal Waters off Goa

Inherent and apparent optical properties were measured for coastal waters off Goa, a site on the west coast of India using the in-situ measuring profiling optical instruments. The optical closure was obtained using the radiative transfer model, Hydrolight (Sequoia Inc.). Hydrolight simulations were carried out at all stations using “average particle” Petzold phase function and Fournier Forand phase function with optimum bbp/bp value. The optical properties derived from Hydrolight simulations were then compared with the measured optical properties. The widely used “average particle” phase function measured by Petzold 1972 for coastal waters was found to provide poor results for most of the stations while for few others it was found to produce results comparable to Fournier Forand phase function. The mean percentage deviation for water leaving radiance (remote sensing reflectance) simulated using Petzold and Fournier Forand phase function for wavelength 488 nm varied from 3.8 to 240.7 % (3.8 to 240.8 %) and 1.0 to 48.9 % (1.0 % to 49.0 %) respectively. These closure studies are essential in strengthening the confidence in models or algorithms developed for ocean color remote sensing and also in better understanding of the marine optical properties of waters of the study area.

Factors affecting the measurement of CDOM by remote sensing of optically complex inland waters

A combination of new measurements and analysis of historical data from several geographic regions was used to address four issues that affect the reliability and interpretation of colored dissolved organic matter (CDOM) measured by remote sensing of inland waters. First, high variability of CDOM levels in lakes and rivers was found at seasonal and multi-year time scales and at shorter intervals in some rivers and lakes. Coefficients of variation (CVs) of 30%–50% for absorptivity at 440nm (a440) were common in historical and new data sets we examined. CDOM values used to calibrate imagery thus should be measured close to the image acquisition date, preferably within 1–2 months in lakes and a few days in large rivers, unless it can be shown that CDOM levels are temporally stable over longer (or shorter) time periods in a given aquatic system. Second, spectral slopes (S) for CDOM in the visible range vary little over time (even over multi-year periods) within sites. Substantial variation was found between sites, however, and most spectra showed a change in slope near 460nm. Values of S400–460 for waters with moderate to high CDOM levels generally were within a narrow range (~0.014–0.018) and similar to reported S values in the near UV. Values of S400–460 for waters with low CDOM generally were smaller and more variable, as were values for S460–650 for all waters. Overall, the variability of spectral slopes in the visible range should not have a large effect on the reliability of a440 estimates made from remote sensing, which in many models involve reflectance measurements at wavelengths>500nm. Third, although a strong correlation (r2=0.925) was found between CDOM levels and DOC concentrations in 34 surface waters sampled in 2013, the standard error of estimate suggests an uncertainty of~±20% in predicting DOC at a440=5m−1 (a moderate CDOM level). Moreover, CDOM–DOC relationships for unpublished data sets we analyzed and those reported in the literature indicate that both the fraction of DOC that is colored and slopes of regressions between CDOM and DOC are highly variable in space and time. Prediction of DOC concentrations in water bodies from CDOM levels (whether measured in the laboratory or by remote sensing) thus is associated with considerable uncertainty. For the present, this implies that field sampling is required to verify DOC concentrations predicted from remotely sensed CDOM measurements until we have a better understanding of variations in DOC–CDOM relationships. Fourth, shapes of reflectance spectra for CDOM-rich waters varied greatly depending on the concentrations of other constituents (suspended solids and chlorophyll) that affect the optical properties of water. Nonetheless, it is not obvious from our results for several predictive models that different remote sensing algorithms are needed to calculate CDOM levels accurately for waters where CDOM is the only variable affecting reflectance versus waters where other constituents also affect the spectra. The best band or band ratio models for simulated Landsat 8, Sentinel-2 and Sentinel-3 bands from field measured reflectance spectra yielded high r2 values (0.84–0.86) for a440. The broader Landsat 8 bands worked nearly as well for a440 as the narrower Sentinel band sets and hyperspectral bands, probably because CDOM is characterized by a broad exponential increase in absorbance with decreasing wavelength rather than specific peaks or troughs in absorbance or reflectance.

Fluorescence measured using a field-portable laser fluorometer as a proxy for CDOM absorption

The colored fraction of dissolved organic matter, CDOM, directly influences water optical properties and spectral quality, playing an important role in aquatic ecosystems, optical remote sensing and carbon circulation in the sea. Measuring in situ CDOM absorption coefficient, however, is difficult because it requires prefiltration of water samples. A field-portable laser fluorometer for fast acquisition of in situ CDOM fluorescence data without sample filtering was developed. Using the instrument in the Yangtze River estuary, the East China Sea coast, the West Lake, and the Qiandao Lake, good estimates of CDOM absorption were obtained from in situ fluorescence measurements. High correlation (r = 0.94) was observed between CDOM absorption coefficient and fluorescence normalized to Raman scattering in diverse water types. Comparison of different methods for measuring CDOM fluorescence was carried out. Fluorescence measured by in situ laser fluorometer compared very well to the values obtained using more sophisticated laboratory spectrophotofluorometer; a significant relationship (r = 0.95) was identified between the two methods. Spatial distributions of CDOM in the Yangtze River estuary and its adjacent sea compiled from discrete samples analyses were presented. A linear relationship was identified between CDOM fluorescence and salinity in surface water, reflecting the potential of CDOM fluorescence to be used as a passive tracer of freshwater input. The in situ measurement results demonstrated the utility of the laser fluorometer for rapid acquisition of high-resolution profiles, and that the work resulting from sample filtration or storage can be avoided.

Modification and validation of a quasi-analytical algorithm for inherent optical properties in the turbid waters of Poyang Lake, China

Knowing the inherent optical properties (IOPs) of water bodies is useful for many water environment studies and applications. To derive the IOPs from remote sensing reflectance, a multiband quasi-analytical algorithm (QAA) was modified and validated for the highly turbid Poyang Lake in China. In order to supplement and expand the dynamic variation range of the measured water optical properties, a Hydrolight simulated dataset was generated to develop a regional QAA (QAA710) for this area. The QAA710 model was then validated with simulated data, simulated data with random noise, and in situ data. The results show that the effects of random noise (within ±20%) of remote-sensing reflectance on the derived total absorption coefficients (at) and the particulate backscattering coefficients (bbp) by the QAA710 model are insignificant (a band-averaged mean relative error of 4.1% and 12.0%, respectively). The validation of in situat shows a 28.6% mean relative difference. The model process, modeling data, and validation data introduce uncertainties into the derived results. These analyses demonstrate that the QAA710 model, based on the characterization of local environments, performs well in retrieving Poyang Lake’s IOPs.

New strategy to improve estimation of diffuse attenuation coefficient for highly turbid inland waters

The diffuse attenuation coefficient, Kd(λ), is an important water optical property. Detection of Kd(λ) by means of remote sensing can provide significant assistance in understanding water environment conditions and many biogeochemical processes. Even when existing algorithms exhibit good performance in clear open ocean and turbid coastal waters, accurate quantification of highly turbid inland water bodies can still be a challenge due to their bio-optical complexity. In this study, we examined the performance of two typical pre-existing Kd(490) models in inland water bodies from Lake Taihu, Lake Chaohu, and the Three Gorges Reservoir in China. On the basis of water optical classification, new Kd(490) models were developed for these waters by means of the support vector machine approach. The obtained results showed that the two pre-existing Kd(490) models presented relatively large errors by comparison with the new models, with mean absolute percentage error (MAPE) values above ~30%. More importantly, among the new models, type-specific models generally outperformed the aggregated model. For water classified as Type 1 + Type 2, the type-specific model produced validation errors with MAPE = 16.8% and RMSE = 0.98 m−1. For water classified as Type 3, the MAPE and RMSE of the type-specific model were found to be 18.8% and 1.85 m−1, respectively. The findings in this study demonstrate that water classification (prior to algorithm development) is needed for the development of excellent Kd(490) retrieval algorithms, and the type-specific models thus developed are an important supplement to existing Kd(490) retrieval models for highly turbid inland waters.

Phytoplankton biomass profiles in San Jorge Bay (Antofagasta, Chile) based on color imagery

Fluorometric measurements were taken from a CTD at San Jorge Bay (northern Chile) to adjust a Gaussian model, in order to determine the vertical distribution of phytoplankton biomass using satellite-derived chlorophyll a data. Calibration was done using two in situ data sets. Each chlorophyll a profile was smoothed by a moving average and adjusted with a Gaussian model, obtaining the mean Gaussian parameters for both data sets. The mean Gaussian model obtained for one of the data sets was valid for a chlorophyll a range between 1.17 and 51.8 mg m–3, and the maximum concentration was located at 19.20 and 0.25 m depth, respectively. The 20 January 2011 color image was analyzed for the study area, and the modal concentration was 0.78 mg m–3, with 95% of the data varying between 0.5 and 20.0 mg m–3. The adjusted mean Gaussian model was valid for 80.26% of the study area. The analysis was expanded to the rest of January 2011 (14 images), and the model was valid for 84.40% (±12.48%) of the study area. The same procedure was followed but without applying the moving average to the in situ data, and the Gaussian model obtained in this case was valid for 93.72% (±8.89%) of the study area. Other studies of the optical properties of water are required for a better interpretation of the color images for this coastal system.

The energy spectrum of vibration of molecules in water and its properties

The energy spectra of vibration of OH and HOH bonds in molecules in liquid water are calculated using the dynamic equation in nonlinearly self-trapping theory. The eigenenergies and eigenfunctions of the first, second, third and nth excited states of stretching vibration of OH bond as well as of first and second excited states of stretching and bending vibrations of HOH bond are obtained, respectively. From comparing them with those obtained in normal model and localized model we find that the calculated results approach more to the experimental values relative to those obtained from normal and local models. These results are helpful to explain well the optical properties of water.

An empirical algorithm to estimate spectral average cosine of underwater light field from remote sensing data in coastal oceanic waters

The underwater average cosine is an apparent optical property of water that describes the angular distribution of radiance at a given point in water. Here, we present a simple empirical algorithm to estimate spectral underwater average cosine µ̅(λ) where the wavelength λ ranges from 400 nm to 700 nm, based only on the apparent optical property, remote sensing reflectance, Rrs(λ), and solar zenith angle. The algorithm has been developed using the measured optical parameters from the coastal waters off Goa, India, and eastern Arabian Sea and the optical parameters derived using the radiative transfer code using these measured data. The algorithm was compared with two earlier reported empirical algorithms of Haltrin (1998, 2000), and the performance of the algorithm was found to be better than these two empirical algorithms. The algorithm is based on single optical parameter; remote sensing reflectance, which can be easily measured in‐situ, and is available from the ocean color satellite sensors; hence this algorithm will find applications in the ocean color remote sensing.

A new simple concept for ocean colour remote sensing using parallel polarisation radiance

Ocean colour remote sensing has supported research on subjects ranging from marine ecosystems to climate change for almost 35 years. However, as the framework for ocean colour remote sensing is based on the radiation intensity at the top-of-atmosphere (TOA), the polarisation of the radiation, which contains additional information on atmospheric and water optical properties, has largely been neglected. In this study, we propose a new simple concept to ocean colour remote sensing that uses parallel polarisation radiance (PPR) instead of the traditional radiation intensity. We use vector radiative transfer simulation and polarimetric satellite sensing data to demonstrate that using PPR has two significant advantages in that it effectively diminishes the sun glint contamination and enhances the ocean colour signal at the TOA. This concept may open new doors for ocean colour remote sensing. We suggest that the next generation of ocean colour sensors should measure PPR to enhance observational capability.

Microplasma‐Induce Liquid Chemistry for Stabilizing of Silicon Nanocrystals Optical Properties in Water

In this report, we demonstrate stabilization of photoluminescence (PL) properties of environmentally and biologically friendly silicon nanocrystals (SiNCs) in water through atmospheric pressure radio‐frequency (RF) microplasma processing at room temperature. The PL of the SiNCs is enhanced after microplasma processing, which involves three‐dimensional engineering of SiNCs directly in water avoiding degradation by surface functionalization. Moreover, we compare the RF microplasma process with direct‐current microplasma processing, whereby the two approaches lead to very similar SiNCs optical properties and surface characteristics. The induced unique chemistry and SiNCs stability in water have wide implications for the SiNCs processability and applications in energy devices, biology and medicine.

Optimizing the Use of Secchi Depth as a Proxy for Euphotic Depth in Coastal Waters: An Empirical Study from the Baltic Sea

Potential zone for photosynthesis in natural waters is restricted to a relatively thin illuminated surface water layer. The thickness of this layer is often indirectly estimated by measuring the depth in which 1% of the photosynthetically active radiation entering the water remains. This depth is referred to as the euphotic depth. A coarser way to evaluate the underwater light penetration is to measure the Secchi depth, which is a visual measure of water transparency. The numerical relationship between these two optical parameters, i.e., conversion coefficient m, varies according to the changes in the optical properties of water, especially in transitional coastal waters. The aim of our study is to assess which is the most suitable criterion to base these coefficients on. We tested nine methods, seven of which were locally calibrated with our own in situ data from the optically heterogeneous Baltic Sea archipelago coast of SW Finland. We managed to significantly improve the accuracy of modeling euphotic depths from Secchi depths by using scalable and locally calibrated methods instead of a single fixed coefficient. The best results were achieved by using methods, either continuous functions or series of constants, which are based on water transparency values.

Connections between physical, optical and biogeochemical processes in the Pacific Ocean

A new biogeochemical model has been developed and coupled to a three-dimensional physical model in the Pacific Ocean. With the explicitly represented dissolved organic pools, this new model is able to link key biogeochemical processes with optical processes. Model validation against satellite and in situ data indicates the model is robust in reproducing general biogeochemical and optical features. Colored dissolved organic matter (CDOM) has been suggested to play an important role in regulating underwater light field. With the coupled model, physical and biological regulations of CDOM in the euphotic zone are analyzed. Model results indicate seasonal variability of CDOM is mostly determined by biological processes, while the importance of physical regulation manifests in the annual mean terms. Without CDOM attenuating light, modeled depth-integrated primary production is about 10% higher than the control run when averaged over the entire basin, while this discrepancy is highly variable in space with magnitudes reaching higher than 100% in some locations. With CDOM dynamics integrated in physical-biological interactions, a new mechanism by which physical processes affect biological processes is suggested, namely, physical transport of CDOM changes water optical properties, which can further modify underwater light field and subsequently affect the distribution of phytoplankton chlorophyll. This mechanism tends to occur in the entire Pacific basin but with strong spatial variability, implying the importance of including optical processes in the coupled physical-biogeochemical model.

Remote Sensing of Water Optical Property for China's Inland Lake Taihu Using the SWIR Atmospheric Correction With 1640 and 2130 nm Bands

Using the shortwave infrared (SWIR) atmospheric correction algorithm with 1640 and 2130 nm bands, water optical property data for China's inland freshwater Lake Taihu have been derived from measurements of the Moderate Resolution Imaging Spectroradiometer (MODIS) on the satellite Aqua. Using MODIS-Aqua measurements from 2002 to 2010, seasonal and spatial distributions of the normalized water-leaving radiance nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (λ) spectra from visible to the near-infrared (NIR) and SWIR (1240 nm) are derived and used for study and characterization of Lake Taihu water optical properties. In particular, for the first time, spatial and seasonal variations of nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (λ) at the SWIR 1240 nm (nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (1240)) are derived for the lake and show some different features from those of the red and NIR nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (λ) (nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (645) and nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (859)). Time series of monthly MODIS-derived nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (λ) spectra for Lake Taihu are obtained and analyzed, showing important seasonal and interannual variations. The results indicate that the SWIR nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (1240) contributions in the lake are mainly due to the presence of significant amounts of algae, while the red and NIR nL <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</sub> (λ) variations result from changes of total suspended sediment (TSS) amounts in the water column. Furthermore, this study shows that all three SWIR bands at 1240, 1640, and 2130 nm are useful and required for satellite water quality remote sensing for extremely turbid near-shore and inland waters.

A time variant investigation on optical properties of water based Al2O3 nanofluid

Optical properties of nanofluids are vital for calculating performance of a Direct Absorption Solar Collector (DASC). Characteristics of nanofluids are not constant; they vary with time and growth of nanoparticles. For current investigation, nanofluids were prepared to obtain considerable stability. Stability ratio of our nanofluids was 100 times larger than the threshold limit. Here, we have investigated aggregation process and its effect on optical characteristics of the nanofluids using Transmission Electron Microscopy (TEM) imaging, Dynamic Light Scattering (DLS) approach and UV–visible spectroscopy. Steps of aggregation are broadly described with TEM images. Our results indicate that extinction coefficients of the nanofluids reduce rapidly with time within visible to near IR region. Quasi Crystalline (QC) and Rayleigh Approaches were used to compare the experimental behavior of optical properties of nanofluids. It was found that both of these approaches are weak to predict the optical behavior, especially at UV region and scattering of light is found responsible for high extinction with the experimental results. More experimental effort is still required to get an appropriate explanation.

Effect of antimicrobial on mechanical, barrier and optical properties of corn starch based self-supporting edible film

Antimicrobials like potassium sorbate, sodium propionate, and benzoic acid were incorporated in corn starch based formulation to investigate their effect on mechanical, water vapour barrier and optical properties of the developed self supporting edible film. The film was prepared by casting technique. When incorporated at 1.40% and above, potassium sorbate decreased the tensile strength (about 22%) and increased the elongation (about 55%) of control film; whereas, it increased the water vapour permeability by 15% only when added at 2.66%. At 2.66%, benzoic acid reduced the tensile strength by 24% and sodium propionate increased elongation by 17%. These two antimicrobials did not change the water vapour permeability. However, all the three antimicrobials adversely affected the optical properties by decreasing the whiteness index, increasing yellowness index, and reducing the surface gloss, with potassium sorbate showing the maximum effect. Among the three antimicrobials, sodium propionate appeared to be the best with minimum deterioration of film properties.

Preparation and Characterization of Nano Particle Reinforced Polyactides Composite

Polylactides (PLA) based composite films modified with nanoclay content ranges from 0-30 wt% were fabricated using solvent casting method and the mechanical properties, water vapor permeability, oxygen barrier, thermal stability and optical properties were studied. The study showed that the addition of up to 15 wt% of clay has caused a significant improvement of tensile strength of the PLA/nanoclay composite film. However, the further increasing of nanoclay content of &gt;15 wt% of nanoclay has caused a significant reduction in tensile, elongation at break and optical properties of PLA matrix. Both the oxygen and water permeability of the PLA/nanoclay composite film decrease with the increasing of nanoclay contents. Greater water barrier properties would be achieved if the high nanoclay contents of 10-30 wt% were dispersed homogenous within the PLA matrix. The addition of nanoclay greater than 10 wt% affected the appearance of the film (i.e. increasing the haze and ΔE). Thermal analysis result has proved that the melting temperature, crystallization temperature and glass transition temperature of the composite film only slightly affected by the addition of nanoclay due to the immobilization polymer chain in the composite film.