Cellulose-Based Visual Label for Wide pH Freshness Detection
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Solution Overview
Problem
Existing freshness indicator films are limited in their indication range and face issues such as moisture absorption and high transparency, making them unsuitable for detecting the freshness of various foods simultaneously and reliably.
Innovation Solution
A multifunctional intelligent cellulose-based visual label is developed through carboxylation modification, cationic grafting, and dye adsorption, allowing it to indicate freshness across a wide pH range with rapid color variation, while maintaining dimensional stability and antibacterial properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If existing freshness indicator films are used, then they can indicate freshness, but they are limited in indication range and cannot detect various kinds of food at the same time
Solution Approach 1:
The patent applies multi-functionality by integrating multiple pH-sensitive dyes (bromothymol blue, methyl red, phenolphthalein) into a single cellulose-based indicator film. Each dye responds to different pH ranges, enabling the film to detect freshness changes across a broad pH spectrum (pH 3-10) suitable for various food types including fruits, vegetables, meat, and dairy products, thus resolving the limitation of narrow indication range while maintaining detection reliability
Solution Approach 2:
The patent uses composite materials by combining cellulose fibers with multiple pH-sensitive dyes and crosslinking agents to create a multifunctional indicator film. The cellulose matrix provides structural stability and porosity, while the embedded dyes provide broad pH sensitivity. This composite structure enables simultaneous detection across different pH ranges without compromising the reliability of individual dye responses
2Illumination intensity
If hydrogel indicator film is used, then it has high transparency, but it absorbs moisture and swells easily
Solution Approach 1:
The patent employs a cellulose-based thin film structure that maintains flexibility and dimensional stability. The cellulose matrix forms a robust network that resists swelling while allowing light transmission. The film's porous structure is controlled to provide mechanical strength without compromising transparency, solving the contradiction between maintaining high transparency and preventing moisture-induced swelling
Solution Approach 2:
The patent applies local quality by creating a heterogeneous cellulose matrix with regions of different porosity and dye concentration. Areas with higher cellulose density provide structural stability and moisture resistance, while regions with controlled porosity allow light transmission and dye-metabolite interaction. This spatial variation in properties enables the film to simultaneously achieve dimensional stability and high transparency
3Illumination intensity
If the indicator film is made more opaque to enhance color observation, then color visibility improves, but dye migration may occur
Solution Approach 1:
The patent applies the nesting principle by embedding pH-sensitive dyes within the cellulose fiber matrix structure. The dyes are trapped inside the porous cellulose network, which prevents their migration while allowing them to interact with metabolic gases. This nested configuration enables the film to maintain opacity for good color observation while securing dye stability through physical containment within the cellulose structure
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
The intelligent label effectively indicates the freshness of foods like milk, pork, and spinach with 100% antibacterial rate against Staphylococcus aureus, ensuring food safety and prolonged shelf life, and its opaque matrix enhances color observation without dye migration.
Implementation Method 1
adding the quaternized fibers into the composite dye solution, placing the composite dye solution added with the quaternized fibers in an oscillating water bath machine to perform an oscillatory adsorption for 3.5 h to 4 h
Implementation Method 2
eluting dyes physically attached to surfaces of the quaternized fibers with sodium hydroxide solution with a concentration of 0.045 mol/L to 0.055 mol/L
Data Source
AI summary
A preparation method and an application method of a multifunctional intelligent cellulose-based visual label are provided. The multifunctional intelligent cellulose-based visual label solved a problem that an existing freshness indicator film is narrowed in an indication range. The preparation method includes the following steps: step 1 of carboxylation modification; step 2 of cationic grafting; step 3 of preparation of a composite dye solution; step 4 of preparation of responsive fibers; and step 5 of performing vacuum filtration to prepare paper, thereby obtaining the multifunctional intelligent cellulose-based visual label. The food freshness is indicated with the obtained intelligent visual label. An indicated pH value range is 4-8, color variation can be completed within 30 seconds, and the food freshness can be accurately indicated. The multifunctional intelligent cellulose-based visual label is low-carbon, efficient, green, safe, and wide in the indication range, and can be used in food monitoring.