Cellophane is a thin, transparent, and flexible sheet material recognized for its distinctive crinkle and clarity. It gained prominence in the early 20th century as an alternative to plastics because it originates from natural, renewable resources. This material has found extensive application in various packaging roles, particularly for food products.
From Raw Cellulose to Viscose Solution
The journey of cellophane begins with cellulose, a natural polymer predominantly sourced from wood pulp. To initiate the transformation, sheets of cellulose are steeped in a concentrated solution of caustic soda, also known as sodium hydroxide. This process converts the cellulose into alkali cellulose.
Following this steeping, excess liquid is pressed from the alkali cellulose, which is then shredded into fine, fluffy particles called “white crumb.” This crumb undergoes an aging process. Subsequently, the aged crumb reacts with carbon disulfide, leading to the formation of sodium cellulose xanthate.
Sodium cellulose xanthate is then dissolved in a weak solution of caustic soda. This dissolution creates a viscous, amber-colored liquid known as “viscose,” which serves as the foundational material for cellophane film. The preparation of this viscose solution is a precise chemical undertaking, preparing the raw cellulose for its next physical transformation.
The Regeneration and Film Formation Process
The viscose solution is pumped through a narrow slit, acting as an extrusion die, directly into a coagulation bath. This bath contains a mixture of sulfuric acid and various salts, such as sodium sulfate.
The acidic environment immediately triggers a chemical reaction with the viscose. The sulfuric acid neutralizes the alkali, causing the sodium cellulose xanthate to decompose. This decomposition regenerates the cellulose back into its solid polymeric form.
As the cellulose regenerates, it precipitates out of the solution, continuously forming a thin, nascent film. The film is guided and stretched by a series of rollers. This mechanical stretching achieves the desired thickness and strength of the film. The simultaneous chemical regeneration and physical shaping are what allow for the continuous creation of the transparent sheet.
Refining and Finishing the Cellophane Film
After the initial formation, the regenerated cellulose film undergoes several washing steps. These washes remove residual acids and salts from the coagulation bath. Following washing, the film may be subjected to bleaching processes to enhance its clarity and eliminate any yellowish tints that might be present.
A subsequent step involves incorporating plasticizers, such as glycerin, into the film structure. These additives impart flexibility, preventing it from becoming brittle and prone to cracking. The amount of plasticizer can be adjusted to achieve different levels of pliability.
The film then passes through heated rollers for drying, removing remaining water. Finally, to tailor cellophane for specific applications, it can be coated with materials like nitrocellulose or other specialized polymers. These coatings improve the film’s barrier properties against moisture, gases, and aromas, broadening its utility in packaging.
Distinct Characteristics from its Manufacturing Process
The manufacturing process, particularly cellulose regeneration, imparts several characteristics to cellophane. Its high transparency results from the uniform re-formation of cellulose fibers during coagulation. This clarity makes it ideal for showcasing packaged contents.
Cellophane also exhibits breathability, allowing some passage of moisture and gases, a property that differs from many synthetic plastic films. This characteristic stems from its regenerated cellulose structure.
Because it is derived directly from cellulose, cellophane is inherently biodegradable, distinguishing its environmental fate from petroleum-based plastics.