Removal of volatile organic compounds and odorous compounds for multilayer packaging recyclates using heated air purging

Multilayer packaging (MLP) is made from Polyethylene terephthalate (PET), Polyethylene (PE), Polypropylene (PP), Ethylene vinyl alcohol (EVOH), Polyvinyl chloride (PVC), and tie layer materials. MLPs are either burned or dumped in landfills after their use, which causes many hazards to humans and the environment. MLPs are recycled in recycling facilities and converted into pellets to reuse them. However, the MLPs are strongly contaminated by volatile organic compounds and odorous compounds, which prevents their use in high-end applications, i.e., cosmetics, packaging, etc. In the research work, a remediation strategy is proposed to reduce VOCs and odorous compounds from MLP recyclates using heated air oven treatments, which are also easily scalable to pilot and industrial scales. VOCs and odor are reduced significantly without compromising the product’s mechanical, thermal, and other properties.


Introduction
The rapid growth of plastic packaging solid waste harms the environment, marine, and human beings.Foil is the main pre-product used in packaging manufacturing, and it is typically made of plastics like polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), polyamide (PA), or polyethylene terephthalate [1].In a few packaging film industries, the film is made from biaxially-oriented polyethylene terephthalate (BOPET), Biaxially oriented polypropylene (BOPP).These materials are combined to create multilayer packaging (MLP), which offers various advantages compared to single-layer materials.Due to enhanced barrier properties from moisture, gases, and other biological contaminants, single-layer plastic film is replaced by multilayer one [2].Due to the increasing demand for packaging materials in recent times, concern about the safety and hygiene of products is forcing a significant development towards advanced techniques and method developments in packaging [3], [4].
MLP waste can be found around our surrounding areas, forests, rivers, and oceans.This plastic waste causes soil and water pollution, and burning it releases many harmful gases, leading to global warming.It leads to many hazardous human diseases such as difficulty breathing, nausea, metabolic, genetic disease, diabetes, and cancer [5]- [8].To reduce plastic wastage, recycling is a mitigating option.Recycling requires good sorting at the source of waste generation, typically households, restaurants, and leisure places like beaches, riversides, etc [9].Post-consumer waste creates more challenges in the circular economy and sustainability [10].
Recycling monolayer packaging material is relatively easier than MLP because of many layers, such as the abrasion layer, adhesive layer, and layer for protection from oxygen and moisture [11], [12].Different mono-material layers are attached, layer by layer, to create the MLP and they are very thin in size.It is practically impossible to detach them from one another [13]- [15].Hence, during mechanical recycling, using extrusion, all the layers are mixed and are not useful for the same packaging application originally served [16].These MLP recyclates, produced from mechanical recycling, are downgraded products.Therefore, we cannot use recycled MLP in high-end applications like food, pharma, automotive, etc.These MLP recyclates also have contaminations, higher amounts of VOCs, and odorous compounds.This is also observed by visiting a mechanical recycling facility [17], [18].
VOCs and odorous compounds from MLP waste can be reduced by exposing the MLP recycling to hot air at elevated temperatures.VOCs are low molecular weight compounds generated during the manufacture and degradation of polymers such as oligomers and monomers.VOCs have high vapor pressure at room temperature; they can migrate into the human nose and eyes and generate health hazards [19], [20].Polymers release small molecules such as oligomers, monomers, VOCs, and odorous compounds.When recycled pellets are heated at elevated temperatures to reduce contamination, we also need to be concerned with other properties, i.e., mechanical, thermal, color, and optical.We cannot compromise the other properties of the materials to use them again in applications.VOCs and odorous compounds in recycled material restrict its use in high-value applications [21]- [23].
Cabanes  [24], [25].These studies were conducted only on HDPE and polyethylene imine materials and limited to only virgin materials.But we need to focus on the waste from the food packaging sector, as it is the largest sector in plastic processing.This research paper focuses on the mechanical recycling of MLP waste, which has not been done until now.Moreover, it is necessary to focus on reducing odor from recycled materials, even in terms of hygiene from VOCs and SVOCs; otherwise, people will not agree to buy that product [26], [27].
We applied remediation strategies on the lab scale using the oven at different temperatures.There are two possibilities to do hot air purging on the materials on an industrial scale.A. Static or batch processing -the heating + purging silo is filled up and heated.After the operation product can be loaded from this silo or transferred to the cooling down silo to free the heating purging silo.B. Continuous set-up -the storage and Heating + purging silos are filled up.A constant product flow from the storage silo to the Heating + purging silo to the cooling down silo can be organized based on the pre-agreed transfer speed.
This research aims to identify VOCs present in recycled polymer film pellets by applying hot air purging or can, say, temperature stripping, followed by the analysis by a human sensory panel and GC-MS [28] After applying oven remediation at different temperatures and times on recycled polymer film pellets, we utilized a human sensory panel and Gas chromatography-mass spectrometry (GC-MS) to evaluate the odorous compounds present in MLPs deeply.Samples will be analyzed with the help of Fourier transform infrared (FT-IR), Thermogravimetric analysis (TGA), Differential scanning calorimeter (DSC), and Tensile tests to check the effect on other properties of recycled pellets.To the best of our knowledge, this research is not conducted so far to evaluate organic contaminants reduction in multilayer packaging film pellets and theoretical study by a sensory panel.
In this research work, hot air oven purging is applied to reduce the VOCs and odorous compounds from the MLP waste.The hot air oven purging process is optimized to reach desired VOC and odor levels.The comparison of the control sample (MLP recyclates) against the hot air oven-purged samples in different conditions is discussed.
UFlex Limited, Noida, India, provided recycled packaging film material as the source of the matrix.These packaging films are discarded after use, and the company collects waste.These packaging films are made of Biaxially Oriented Polyethylene Terephthalate (BOPET), Biaxially Oriented Polypropylene (BOPP) films, and Cast Polypropylene (CPP) films.For recycling, these films are collected, segregated, and processed for further cleaning and converted into pellets with the help of extrusion and various techniques.
The recycled packaging pellets are mostly circular with a diameter of 4 mm.In contrast, films are typically made from superior packaging for a wide range of products, including snacks, candy and confectionery, sugar, rice and other cereals, beverages, tea and coffee, dessert mixes, noodles, wheat flour, soaps and detergents, shampoos & conditioners, vegetable oil, spices, marinates & pastes, cheese and dairy products, anti-fog, pet food, pharmaceuticals, contraceptives, garden fertilizers and plant nutrients, motor oil, and lubricants.A 50 gm sample is kept in a polyethylene polymer bag for standard analysis.Six sets of 10 gm samples at 70 ℃, 6 10 gm samples at 90 ℃, and 6 10 gm samples at 110 ℃ were kept for oven studies.The timings for those samples to stay in the oven were 24, 48, 72, 96, 120, and 144 of one set at a constant temperature.
For the sensory evaluation, six sets of 10 gm samples were kept in the oven for 1-6 days at 70-, 90-, and 110-degree Celsius temperatures.Every day one petri disk was pulled out from the oven and transferred to a polyethylene Ziplock bag after cooling for 30 s.These bags were stored on a shelf without interaction with UV light.After completing six days with one temperature sample, the panelist sniffed standards.

Sensory Analysis
The samples listed were analyzed by the sensory panel for odor intensity.We can observe that hot air purging helped to reduce the odor intensity values.In the sensory analysis, all the samples are remediated by hot air purging at different temperatures and times.We have observed the odor intensity decreasing as the oven time increases for the sample.As we mentioned in Figure 1(a).Treatment at 70 ℃ was effective.The intensity of non-treated or standard samples was maximum.After 24 hours, a slightly decreased has been noted in the intensity because of the removal of VOCs from the material.On day six, the intensity was reduced by approximately 80 % during the hot air purging step.
In Figure 1(b), purging is done at 90 ℃ at the same repeated time compared to 70 ℃.The reduction in the intensity during hot air purging at 90 ℃ was more effective; approximately 90 % reduction was  1(c) depicts the treatment information at 110 ℃, and we observed a 100 % reduction in odor sensory analysis.This achievement is noted simultaneously, and the same procedure is done at 70 ℃ and 90 ℃.The average intensity is illustrated in Figure1(d) at 70 ℃, 90 ℃, and 110 ℃ temperatures.As the temperature increases, the odor from the recycled material decreases.

Identification of odorous compounds in the samples
VOCs and odorous compounds can be identified with the help of Gas chromatography-mass spectrometry.The agitation temperature was 100 ℃, and the agitation time was 15 minutes to heat the sample.A good resolution was obtained, some peaks were merged, and the height, intensity, and retention time were observed in the quantification procedure.
A peak height >50,000 has been set as a threshold for identification.The results define the compounds' names, CAS number, and m/z values.Aldehydes, benzene, benzene derivatives, ketones, hydrocarbons, siloxanes, and many more organic compounds are reported by X-caliber and INST libraries.Oxidation, reduction, and degradation of polymers could be the reason for generating VOCs and semi-VOCs from recycled materials.2 (c) VOCs were reduced in high values.GC-MS is defined as the supported analytical technique for the sensory panel analysis because the intensity of VOCs can be observed from it that can be theoretically calculated in sensory panel analysis.

TGA Analysis.
TGA analysis was conducted to study the weight loss and weight derivative of the standard MLP materials and materials after hot air purging experiments.The onset temperature for degradation (T onset ) has been reported in Figure 3.After the experiments, the materials show no change in Tg values, weight percentage, or weight derivative.It means heating the recycled sample at a different temperature to remove the VOCs, SVOCs, and odorous compounds.There is no change in the properties of the materials.So, this method could be a relevant strategy for reducing organic contamination, and we can reuse the materials in high-value applications.Some parameters for TGA analysis, such as T o , T 50 , T m , and wt % for all the materials, are mentioned in Table 1.Temperature 445 ℃ defines the presence of PET.

Conclusions
Heated air purging was applied to reduce VOCs and odorous compounds from the MLP recyclates.MLP recyclates were kept in the hot air oven for different durations at different temperatures.Hot air oven purging conditions were optimized to identify the most suitable treatment conditions.A 100 % reduction in odorous compounds and a 70 % reduction in VOCs were observed during this experimental work.The mechanical, rheological, and thermal properties of the treated materials are not decreased even when treated at 110 ℃ with hot air for VOC removal.This type of remediation can be easily scaled up on the industrial scale by installing heated air purging capabilities in the storage silos.The remediation process can be applied in both static and continuous mode.Removal of VOCs and odorous compounds from the MLP recycles makes it possible to use them for relatively high-end applications and potentially opens the possibility of using them for food packaging.Using waste material with reduced contamination, fewer VOCs, and no odorous compounds opens the way toward sustainability and a circular economy.
2) Use of recycled materials for high value applications.
3) We can scaleup the idea into industries for ~200 tons waste.

Disadvantages:
1) For different polymers, temperature would be different due to its melting point.

Figure 1 .
Figure 1.Graph for sensory analysis from panellists at different temperatures and average intensity.

Figure 2 (
Figure 2(a) shows samples kept at 70 ℃ for six days.It can be observed from the intensity peaks of the compounds.It was decreasing from day 1 to day 6 for many VOCs.Figure 2(b) defined the intensity of VOCs when kept at 90 ℃.It shows a major decrement because of high-temperature purging on samples.It shows a large reduction in the intensity area of the VOCs.It has been observed in Figure 2 (c) VOCs were reduced in high values.GC-MS is defined as the supported analytical technique for the sensory panel analysis because the intensity of VOCs can be observed from it that can be theoretically calculated in sensory panel analysis.

Figure 2 (
Figure 2(a) shows samples kept at 70 ℃ for six days.It can be observed from the intensity peaks of the compounds.It was decreasing from day 1 to day 6 for many VOCs.Figure 2(b) defined the intensity of VOCs when kept at 90 ℃.It shows a major decrement because of high-temperature purging on samples.It shows a large reduction in the intensity area of the VOCs.It has been observed in Figure 2 (c) VOCs were reduced in high values.GC-MS is defined as the supported analytical technique for the sensory panel analysis because the intensity of VOCs can be observed from it that can be theoretically calculated in sensory panel analysis.

10th
Global Conference on Polymer and Composite Materials (PCM 2023)

Figure 3 .
Figure 3. TGA curve for all the recycled material with weight % vs temperature.

3. 4
FT-IR AnalysisThe FT-IR graph, an IR spectrum, provides valuable information about a sample's chemical composition and molecular structure.On the x-axis, Figure represents the wave number in cm -1, which is the reciprocal of the wavelength of infrared radiation.On the y-axis, the graph represents the absorbance or transmittance of the sample at each wave number.The values on the FT-IR graph indicate the different functional groups and chemical bonds present in the sample.Each type of bond absorbs infrared radiation at a specific wavenumber.

Figure 4 .
Figure 4. FT-IR curve for the standard sample and samples after remediation at different temperatures.

Figure 4
Figure4shows a sharp band at ~2800 cm-1 due to intramolecular hydrogen bonding in the alkane group (C-H stretching).The second peak was observed at ~1700 cm -1 , i.e., due to C=O stretching in the . et al., Cohen.et al., Lok.et al., Prado.et al. did their work to reduce the odorous compounds from recycled HDPE bottles, Poly (ethylene imine), HDPE-Lignin Blend, and automotive components by applying different processes respectively