Client Citation Analysis
The Dropometer measured the sessile water contact angle of the optimized wheat straw film, initially and at 10, 20 and 30 s. It did not measure strength, vapour permeability, colour, optics, FTIR, biodegradation or grape quality. Contact angle was not one of the three responses used to choose the formulation.
Static sessile drop water contact angle, read over 30 s and fitted to a decay equation to give a wetting rate constant.
Which mix of wheat straw cellulose, calcium chloride and glycerol gives a strong, flexible, moisture resistant film, and does that film keep grapes fresh at room temperature?
The optimized film (0.5 g cellulose, 556.35 mM CaCl2, 1.5% glycerol) is hydrophilic with moderate wetting kinetics, and it kept grapes intact for 15 days while polystyrene film led to cracked berries.
This study uses water contact angle as one of many checks on a cellulose packaging film made from crop residue.
Water contact angle of the optimized film, read with the Dropometer from a smartphone image of a sessile drop. Readings were taken at the start and at 10, 20 and 30 s, and the fall in angle was fitted to a decay equation.
A texture analyzer gave tensile strength and elongation. A desiccant cup method gave water vapour permeability. Other tests covered colour, thickness, moisture, solubility, water uptake, UV and visible transmittance, DPPH antioxidant activity, FTIR, soil biodegradation and grape quality over 15 days.
Sessile drop water contact angle of the optimized film, initially and at 10, 20 and 30 s, using its dropper and smartphone imaging
Tensile strength and elongation at break of film strips
Water vapour permeability at 25 °C
Hunter L*a*b* colour, whiteness, yellowness and total colour difference
Light transmittance, transparency, UV blocking and DPPH antioxidant absorbance
Infrared spectra of the extracted cellulose and the optimized film
Thickness, moisture content and solubility, and grape soluble solids and pH
The Dropometer measured one property: the water contact angle of the optimized wheat straw cellulose film. A sessile water drop was placed with the instrument's dropper and imaged with a smartphone.
The angle started at 77.3 ± 1.9° and fell to 65.6 ± 1.8° over 30 s. The authors fitted this decline to a decay equation and reported a wetting rate constant of 0.005 s⁻¹.
Contact angle did not drive the formulation choice. The optimization used tensile strength, elongation and vapour permeability, and the grape trial used weight loss, chemistry and visual checks. Contact angle was measured only on the final film.
The time resolved angle showed that the film surface is hydrophilic and wets at a moderate rate. That fits the paper's reading of the solubility and water uptake data, without being a deciding result on its own.
Want to track how water wets your packaging films over the first 30 seconds, reading by reading? See how the Dropometer handles this measurement.
The Dropometer gave an initial water contact angle of 77.3 ± 1.9° on the optimized film, below the 90° line the authors use for hydrophobic.
The angle fell to 65.6 ± 1.8° over 30 s, giving a wetting rate constant of 0.005 s⁻¹, which the authors class as moderate.
Separate tests found 21.36 ± 4.26% solubility and 42.89 ± 0.14% water absorption after 120 min, which the authors relate to the moderate wetting seen in the angle readings.
The optimized film reached 30.82 ± 4.70 MPa tensile strength and 0.59 ± 0.06 × 10⁻¹⁰ g m⁻¹ s⁻¹ Pa⁻¹ vapour permeability, close to model predictions.
Grapes under the wheat straw film lost about 21% weight by day 15 but did not crack, while grapes under polystyrene film cracked by day 9.
One figure panel contains Dropometer data. The paper is published open access under a Creative Commons Attribution (CC BY) licence, as stated in the text.
Panel e plots the optimized film's water contact angle at 10 s intervals up to 30 s, measured with the Dropometer. Panels a to d show transmittance, water absorption, biodegradation and colour from other methods. Credit: Bhattarai and Janaswamy, Foods 2026, CC BY.
Cellulose films from crop residue absorb water, so packaging developers need to know how fast a surface wets, not only its first angle. A short time series shows that difference.
This film read 77.3° at first but 65.6° after 30 s. Reporting only one time point would hide the steady spreading and uptake.
Fitting the decline to a decay equation gives one number, here 0.005 s⁻¹, that can be compared across cellulose films.
The same group has used the Dropometer on alfalfa, soyhull and corncob films, so results sit alongside earlier work from one lab.
Hydrophilic film surface with moderate wetting
Contact angle read at four time points over 30 s
Supports solubility and water uptake results
Optimized film kept grapes free of cracking for 15 days
On absorbing films, take readings at fixed times such as 0, 10, 20 and 30 s rather than one snapshot.
Drop size affects how fast a drop spreads and soaks in. State the volume and its units with every result.
This paper does not give temperature, humidity or which film side was tested. Logging them makes your results easier to repeat.
It measured the water contact angle of the optimized wheat straw cellulose film by the sessile drop method. Readings were taken at the start and at 10, 20 and 30 s. All other properties came from other instruments.
No. The initial angle was 77.3 ± 1.9°, which the authors class as hydrophilic. The angle then fell to 65.6 ± 1.8° over 30 s as the drop spread and soaked in.
It summarises how fast the contact angle falls over time. The paper reports 0.005 s⁻¹ and, citing earlier work, places this between fast wetting (above 0.01) and slow wetting (below 0.002) surfaces.
No. The recipe was chosen to maximise tensile strength and elongation and to minimise vapour permeability. Contact angle was measured afterwards on the chosen film as part of its characterization.
Use the formal reference below when citing the original paper.
Bhattarai, S., & Janaswamy, S. (2026). Valorization of wheat straw cellulose into biodegradable packaging films for fresh produce preservation. Foods, 15(17), 3111. https://doi.org/10.3390/foods15173111
Bhattarai and Janaswamy, Foods 2026, 15, 3111. DOI: 10.3390/foods15173111