A Must-Read for Film Manufacturers | Learn in 3 Minutes: How to Quickly Determine Whether Recycled Material Has Been Added to the Film?

Preface 

As a core product in the membrane industry, thin films are widely used in packaging, construction materials, electronics, and other sectors, and their quality directly impacts both user safety and corporate reputation. To cut costs, some unscrupulous manufacturers adulterate virgin-grade films with recycled materials. Although the difference may appear minor, such practices can significantly compromise the film’s toughness, transparency, and resistance to aging—and in food and medical applications, they may even leach harmful substances, creating serious safety and compliance risks. 

As a WeChat public account dedicated to the membrane industry, we frequently receive inquiries from membrane manufacturers and purchasers: How can one quickly determine whether a thin film contains recycled materials? The key method lies in “ Looks slightly yellow. ”“ Smell of burning ” By combining these two straightforward techniques with auxiliary methods such as tactile feel and specific gravity, it is possible to meet all scenario-specific identification needs. This article will break down the approach point by point, balancing practicality with technical rigor, to help film manufacturers and purchasers avoid the trap of recycled materials. 

I. Core Understanding: What are the specific hazards of using thin films combined with recycled materials? 

Before outlining the identification methods, it’s important to understand why we need to be vigilant about films containing recycled materials. —— Recycled materials have complex origins and, if not rigorously processed, may retain impurities and harmful substances, which not only compromise film performance but also pose multiple risks: 

(1) Sharp performance decline, increasing industry losses 

Recycled materials, after multiple cycles of melt processing, experience molecular chain scission, resulting in significantly inferior performance compared with virgin materials. Films containing recycled content are prone to tearing and exhibit poor resistance to both high and low temperatures; for example, packaging films may easily rupture, leading to product leakage, while construction-material films may age and crack more rapidly. This directly increases rework and material-loss costs for enterprises and fails to meet standard requirements for normal use. 

(2) Safety hazards that threaten a healthy environment 

When recycled materials originate from medical waste plastics, pesticide packaging, and similar sources, they may contain residual heavy metals and toxic additives. In applications involving direct contact with food or medical films, these harmful substances can readily migrate, posing risks to human health; moreover, recycled materials often exhibit poor stability, releasing harmful gases during use and thereby polluting the environment. 

(3) Damage to reputation and exposure to compliance penalties 

The food, pharmaceutical, and high-end electronics industries have extremely stringent requirements for film purity and explicitly prohibit the use of products containing recycled materials. If a company violates these regulations, it will not only lose customer trust but may also breach industry laws and regulations, resulting in market sanctions and damage to its brand reputation. 

II. Core Differentiation Techniques: 2 An intuitive method for quick preliminary assessment 

Membrane companies handle production and testing, while purchasers conduct on-site inspections—no specialized equipment required; master “ Visual inspection ”“ Combustion identification ” With just two core techniques, you can quickly make a preliminary assessment of whether a film contains recycled material, among which “ Slightly yellowish in appearance ”“ Pungent burning smell ” is the most critical criterion for judgment. 

(1) Techniques 1 : Look at the appearance —— Keep a close eye on yellowish tints, impurities, and cuts. 

New-material films exhibit high raw-material purity and a uniform, pristine appearance; in contrast, films containing recycled materials show noticeable visual differences due to impurities and aging. The key observation points are as follows: 

• Check the color: new material PE 、 PP The film should have uniform color and luster; transparent films should be clear and bright with no yellowing, while colored films should be vibrant and free from grayish tones; films containing recycled materials Overall yellowish and grayish The transparent film exhibits a hazy yellow tint, with yellowing becoming more pronounced as the proportion of recycled material increases, particularly at the edges or in thicker sections. 
• Inspect for impurities: New-material film has a smooth surface free of particles, with no obvious black spots or fibers visible in transmitted light; films containing recycled material exhibit fine black spots and impurity particles on the surface, and these are clearly visible in transmitted light. “ Misty feel ” , transparency has declined significantly. 
• Examining the cut edge and toughness: Films made from virgin materials exhibit a smooth, even cut with no burrs or delamination; in contrast, films containing recycled content have a rough, fuzzy cut edge that easily flakes off. When pulled, virgin-material films demonstrate excellent toughness, stretching and rebounding without visible white streaks, whereas recycled-content films are prone to tearing, show obvious white streaks upon stretching, and produce a rough fracture surface. 
• Sunlight exposure test: Some manufacturers use whitening agents to mask yellowing, then expose the film to direct sunlight. 1-2 Over time, films containing recycled materials will yellow and discolor rapidly, whereas films made from virgin materials retain their original color. 

(2) Techniques 2 : Combustion identification —— Smell the aroma, observe the flame, and examine the ash. 

The combustion characteristics of plastic films are directly related to the purity of the raw materials; there is a significant difference in combustion behavior between virgin films and those containing recycled content. (Note: Operations must be conducted in a well-ventilated, safe environment to mitigate fire risks.) 

1. Operating steps: Take 1 cm × 1 cm Take a small piece of the film, ignite it with a lighter, observe the flame and burning rate, smell the odor, and examine the ash after it has extinguished. 

2. Combustion characteristics of new-material films (commonly used film materials): 

• PE Membrane: flame is blue, burns rapidly, has a faint paraffin odor with no pungency, and produces fine, white ash that crumbles easily; 
• PP Membrane: flame is blue with a slight black smoke; odor is faint, resembling burning petroleum; ash is gray-white and loose. 
• PET Membrane: flame is yellow, burns slowly with a slight sweet odor; ash is black, brittle, and hard. 

3. Combustion characteristics of films containing recycled materials: 

• Abnormal flame: predominantly yellow or orange, accompanied by copious black smoke; the flame is unstable and occasionally emits crackling sounds (due to the combustion of impurities). 
• Pungent odor (key distinction): Residual impurities and additives in recycled materials release a burnt, acrid, or foul odor when burned, which is markedly different from the mild, clean scent of virgin materials. 
• Ash anomaly: The ash is dark black and hard, difficult to crush, with residual black particles and carbon residue; some samples exhibit oily secretions. 

Note: The proportion of recycled material added is less than 10% At times, the odor of burning may be subtle and must be assessed in conjunction with visual inspection; burning is strictly prohibited. PVC The membrane releases toxic hydrogen chloride gas upon combustion, posing a health hazard. 

III. Advanced Identification Methods: 3 A tip to improve judgment accuracy 

In stringent applications such as food, pharmaceuticals, and high-end electronics, relying solely on visual inspection and combustion testing is insufficient; additional measures are required. 3 An advanced technique that requires no specialized equipment, further enhancing judgment accuracy and easy for both film manufacturers and purchasers to implement. 

(1) Techniques 3 : Hand feel touch —— Determine purity by touch 

There is a significant difference in the tactile feel between virgin film and film containing recycled materials, which can be used for quick identification: 

• New-material film: smooth and delicate to the touch, with no grainy texture; it produces a crisp rustling sound when rubbed, with no astringent feel, and any creases formed during rubbing quickly spring back. 
• Film containing recycled materials: feels rough and sticky to the touch, with a fine particulate texture; crinkling produces a dull, muffled sound; it wrinkles easily and is difficult to smooth out; in some cases, it may even stick to the hands (due to impurities or additives in the recycled material). 

(2) Techniques 4 : Specific Gravity Test —— Judging based on density differences 

With membrane material density held constant, virgin film exhibits uniform density; however, the presence of recycled content can cause density variations due to impurities. This can be readily assessed through a simple specific-gravity test: 

1. Operating method: Prepare a glass of clean water (density 1 g/cm³ ), take a small piece of the film (after removing any air bubbles) and place it in water to observe its buoyancy; 

2. Criteria for determination: 

• PE 、 PP Film: New-material film will float on the water surface and remain stable; films containing recycled materials, due to their higher impurity density, tend to sink, hover midway between sinking and floating, or exhibit unstable floating. 
• PET Membrane: New-grade material will sink; thin films containing a high proportion of recycled material, due to the presence of low-density impurities, will sink more slowly and may even exhibit a semi-floating state. 

Note: This method is applicable only to virgin film; composite films (such as PET/PE ) Requires comprehensive judgment in conjunction with other methods. 

(3) Techniques 5 : Thermal Stability Test —— View heating reaction 

Recycled materials exhibit poor thermal stability and tend to yellow and deform upon heating, whereas virgin film demonstrates good thermal stability; this can be verified through thermal testing. 

1. Operating procedure: Take a small piece of film and blow it with a medium-to-high-temperature hair dryer. 30-60 Seconds, observe the changes; 

2. Criteria for determination: 

• New-material film: exhibits only slight softening, with no noticeable yellowing or deformation; returns to its original state upon cooling and is odorless. 
• Film containing recycled materials: yellows rapidly, deforms, and may even melt and drip; once cooled, it cannot be restored to its original state, while emitting a pungent, acrid odor (similar to the smell of burning). 

IV. Professional Testing Methods: Precise Quantification, Tailored for Rigorous Scenarios 

In applications such as food and pharmaceuticals, where purity requirements are extremely stringent, the proportion of recycled materials added must be quantitatively determined through specialized testing to ensure compliance and quality. The following are commonly used professional testing methods, which film manufacturers may select as needed: 

(1) Fourier Transform Infrared Spectroscopy Infrared Spectroscopy Testing 

Analysis of the chemical composition of thin films reveals that virgin-material films exhibit clear, single spectral peaks, whereas films containing recycled materials display additional spectral peaks due to impurities and multiple plastic components, enabling precise determination of the presence and approximate type of recycled content. 

(2) DSC Differential Scanning Calorimetry 

Detect the melting point and crystallinity of the film; after multiple reprocessing cycles, the recycled material exhibits a decreased melting point and non-uniform crystallinity, as determined by DSC The curve enables precise quantification of the recycled material addition ratio, with error controlled within 5% Within. 

(3) TGA Thermogravimetric analysis testing 

The weight changes of the film at different temperatures were monitored. The thermogravimetric curve of virgin film was smooth and stable, whereas the film containing recycled material exhibited multiple weight-loss peaks due to the varying thermal stability of impurities, allowing for the determination of the recycled-material content and impurity levels. 

V. Practical Recommendations: How Can Membrane Manufacturers and Purchasers Avoid the Recycled-Feedstock Trap? 

Once you have mastered the identification methods, combine them with the following practical recommendations to control film quality at the source, mitigate risks, and meet the requirements of every stage of the process: 

(1) Procurement Side: Source Control and Rigorous Inspection 

1. Select reputable suppliers: Give priority to those with proper qualifications, a strong reputation, and large scale; request test reports (for purity and harmful substances); and ensure that the contract clearly outlines all terms. “ The addition of recycled materials is prohibited. ” , and agree on liability for breach of contract; 

2. On-site inspection is a must: conduct it promptly after sampling. “ Appearance + Combustion ” Conduct preliminary screening; send key orders to accredited testing institutions for verification to ensure compliance. 

3. Avoid the low-price trap: Films containing recycled materials typically cost less than those made from virgin resin. 10%-30% Be on guard when encountering products priced significantly below the market average to avoid falling into traps due to low prices. 

(2) Production Side: Strict Process Control and Standardized Quality 

1. Strict raw-material selection: Procure only virgin petrochemical-grade materials and require comprehensive material test reports to prevent adulteration. “ Fake new material ”；

2. Production Quality Control: Strengthen multi-stage inspections throughout the production process, conduct regular tests on appearance, combustion performance, and tactile feel, and promptly identify and address any issues. 

3. Clear labeling of intended use: If recycled materials are to be used, their applicable applications must be clearly indicated (use in sensitive sectors such as food and pharmaceuticals is prohibited), and they must comply with relevant standards to avoid non-compliance. 

Conclusion 

The key to determining whether a film contains recycled content lies in “ Slightly yellowish in appearance ”“ Pungent burning smell ” Two intuitive techniques, combined with advanced methods such as tactile feedback, specific gravity, and thermal stability, can cover the vast majority of application scenarios; for stringent applications, however, precise quantification through professional testing is essential to ensure compliance and meet regulatory requirements. 

For membrane manufacturers, stringent control over the incorporation of recycled materials is essential for upholding product quality and building core competitiveness; for purchasers, mastering identification techniques is the key to avoiding market traps and ensuring procurement quality. The healthy development of the membrane industry hinges on industry players’ unwavering commitment to quality and adherence to industry standards. It is our hope that this article will help both membrane manufacturers and purchasers quickly acquire effective identification methods, thereby jointly advancing the membrane industry toward higher quality and greater standardization.