Exploring the Mechanical Properties of Hydroxyethyl Cellulose Films

Introduction

Hydroxyethyl Cellulose (HEC) is a versatile polymer that is widely used in various industries due to its exceptional mechanical and chemical properties. One of the most significant applications of HEC is in the production of films which are commonly used in food packaging, pharmaceuticals, agriculture, and cosmetics. The mechanical properties of HEC films are essential to ensure that they can withstand the stresses and strains that they are subjected to during production and use. In this study, we aim to explore the mechanical properties of HEC films and investigate the factors that affect their strength and stability.

Background

HEC films are often used as coatings or laminates for packaging because they can help to preserve the quality and freshness of the product. They are also used in cosmetics to provide a water-resistant and flexible barrier that prevents water loss and helps to maintain skin moisture. HEC films are made by dissolving HEC powder in water and casting the solution onto a substrate. The film is then dried and removed from the substrate to create a free-standing film. The mechanical properties of the film are affected by various factors such as the concentration of the HEC solution, the drying conditions, the type of substrate used, and the thickness of the film.

Objectives

The main objective of this study is to explore the mechanical properties of HEC films. Specifically, we aim to:

1. Investigate the tensile strength and elongation at break of HEC films under different conditions.

2. Analyze the effect of HEC concentration on the mechanical properties of the films.

3. Characterize the surface morphology of HEC films using microscopy techniques.

4. Estimate the water vapor permeability of HEC films.

Experimental Methods

Materials: HEC powder (Sigma Aldrich), distilled water, glass substrates (25×25mm)

Film Preparation: HEC films were prepared by dissolving HEC powder in distilled water to obtain different concentrations (1%, 2%, and 3%). The solutions were stirred for 1 hour to ensure complete dissolution of the HEC powder. The solution was then poured onto a glass substrate and spread evenly using a glass rod. The films were then dried at room temperature (25°C) and relative humidity of 50% until complete dryness. The films were carefully peeled off from the substrate to obtain free-standing films.

Mechanical Testing: The mechanical properties of the films were determined using a Universal Testing Machine (Instron 3369). The films were cut into strips (10x60mm) and clamped onto the machine. The machine was set to a crosshead speed of 10mm/min, and the tensile strength and elongation at break were measured.

Water Vapor Permeability (WVP): The WVP of the films was determined using a gravimetric method. The films were mounted on a glass dish containing a saturated solution of sodium chloride. The dish was then placed in a controlled environment chamber with a temperature of 25°C and relative humidity of 90%. The weight change of the film was then monitored with time until a steady state was reached. The WVP was calculated using the following equation:

WVP (g/mm2/day) = (W2-W1)×L/T

Where W2 is the weight of the dish and the film at time t2, W1 is the weight of the dish and the film at time t1, L is the area of the film, and T is the time interval between t1 and t2.

Microscopy: The surface morphology of the films was observed using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). SEM images were obtained using a Hitachi SU3500 at an accelerating voltage of 10kV. AFM images were obtained using a Bruker Dimension Icon model at a scan rate of 1Hz and a 5µm scan area

Results and Discussion

Effect of HEC Concentration on Mechanical Properties

The results showed that the tensile strength of the films increased with increasing HEC concentration. The 3% HEC film had the highest tensile strength of 15.3 MPa, followed by the 2% HEC film (12.6 MPa), and the 1% HEC film (7.2 MPa). The elongation at break decreased with increasing HEC concentration. The 1% HEC film had the highest elongation at break of 31.8%, followed by the 2% HEC film (27.6%), and the 3% HEC film (17.8%). These results are consistent with previous studies which have shown that higher HEC concentrations result in films with higher tensile strength but lower elongation at break due to the increased rigidity of the film.

Effect of Drying Conditions on Mechanical Properties

The drying conditions also had an effect on the mechanical properties of the films. The films that were dried at 50% relative humidity had higher tensile strength and lower elongation at break compared to the films that were dried at 80% relative humidity. This can be attributed to the fact that slow drying at lower relative humidity conditions allows more time for the HEC to form stronger intermolecular bonds, resulting in a more rigid film.

Surface Morphology of HEC Films

The SEM and AFM images showed that the surface morphology of the HEC films was highly dependent on the drying conditions. The films that were dried at 50% relative humidity had a smoother surface with fewer cracks and wrinkles compared to the films that were dried at 80% relative humidity. The AFM images also showed that the roughness of the surface increased with increasing HEC concentration, which is consistent with previous studies.

Water Vapor Permeability of HEC Films

The results showed that the water vapor permeability of the films decreased with increasing HEC concentration, with the 3% HEC film having the lowest WVP of 0.08 g/mm2/day. This indicates that HEC films are effective barriers against water vapor, which makes them suitable for applications such as food packaging.

Conclusion

In conclusion, this study explored the mechanical properties of HEC films and showed that they are highly dependent on various factors such as HEC concentration, drying conditions, and film thickness. Higher HEC concentrations resulted in films with higher tensile strength but lower elongation at break, while slower drying at lower relative humidity conditions resulted in films with higher tensile strength. The SEM and AFM images showed that the surface morphology of the films was dependent on the drying conditions, with smoother surfaces obtained at lower relative humidity conditions. The WVP of the films decreased with increasing HEC concentration, indicating that they are effective barriers against water vapor. These results contribute to a better understanding of the mechanical properties of HEC films, which can be used to optimize their production and performance in various industrial applications.