Microfibrillated Cellulose Film Casting with Intermediate Drying
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Solution Overview
Problem
Existing methods for manufacturing microfibrillated cellulose (MFC) films using casting technology face issues with slow water diffusion during drying, leading to cracks, voids, and reduced strength, and require high amounts of plasticizers, which are undesirable, especially in food packaging.
Innovation Solution
A method involving multiple layers of MFC suspensions applied on a non-porous substrate with intermediate drying steps to enhance drying efficiency and reduce plasticizer usage, using spray coating and drying methods like hot air or microwaves to achieve a thin, high-strength film with improved barrier properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the drying speed is increased to improve productivity, then the drying rate increases, but voids or cracks may be formed in the film deteriorating its properties
Solution Approach 1:
The drying process is divided into multiple stages with different temperature conditions. The first drying stage uses a lower temperature (40-80°C) to remove surface water without causing rapid internal evaporation that would create voids or cracks. The second drying stage uses a higher temperature (80-150°C) to complete the drying process after the film structure is already formed and stable.
2Ease of operation
If a large amount of plasticizers is added to improve stretchability, then the film becomes more flexible, but the mechanical and barrier properties of the film deteriorate
Solution Approach 1:
The invention changes the chemical composition parameters of the suspension by incorporating specific additives (surfactants, binders, or coupling agents) that modify the surface properties and interfacial adhesion of MFC fibrils. This allows the film to achieve improved stretchability and mechanical properties through physical and chemical modifications rather than relying on plasticizers.
3Reliability
If the film thickness is reduced to improve barrier properties, then the OTR decreases, but the film strength may be compromised
Solution Approach 1:
The invention creates a composite material system where MFC fibrils are combined with additives (surfactants, binders, or coupling agents) that form a network structure within the thin film. This composite structure provides both the oxygen barrier properties through the dense fibril arrangement and the mechanical strength through the reinforced network, enabling thin films with OTR below 10 ml/m2/24h at 50% RH to maintain adequate strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method produces MFC films with enhanced strength, barrier properties, and reduced plasticizer content, avoiding the drawbacks of traditional casting processes while maintaining high efficiency and energy savings.
Implementation Method 1
drying said first web to a solids content of at least 50 wt % (calculated on the total weight of said web) in an intermediate drying step
Implementation Method 2
drying the web, comprising said first and second web, in a final drying step to form a film
Data Source
AI summary
The method of the invention relates to a method of manufacturing a fibrous, oxygen barrier film by casting a suspension comprising microfibrillated cellulose onto a non-porous substrate in a number of subsequent steps with intermediate drying. The invention enables an efficient method to manufacture an MFC film by casting technology without the problems of cracks or voids formed in the film. By applying the MFC in several layers, with in-between drying, the distance the water has to diffuse through is shorter, whereby the evaporation is more efficient and the film properties are not negatively affected by the drying.