Heat-sealing and microscopic evaluation of paper-based coated materials using various seal bar geometries in vertical form fill seal machine

With the growing emphasis on minimization of global plastic waste, flexible fibre-based packaging has gained significant interest over the past few years. Heat-sealing technology is commonly applied for vertical form-fill-seal machine to provide tight closure of packages for maintaining food quality and shelf life. Several different seal bar geometries and adequate heat-seal parameters are required to improve the seal tightness of the packages. This study aims to compare the heat sealability of thermo-plastic film (OPP/PE) and paper-based materials in vertical form-fill-seal machine using various seal bar profiles. The investigation includes seal strength measurement, understanding the causes of leak formation, seal tightness and inspection of the seal using scanning electron microscopy. Results reveal that OPP/PE material has exceptional seal strength and leakproof ability compared with paper-based materials. However, it has limited operating window because the material shrinks and coarsens at approximately 140 (cid:1) C. Sealing temperature and dwell time are found to be the major factors affecting the seal strength of paper-based material. Results reveal the PE-coated papers exhibit nearly twice the seal strength compared with the dispersion-coated paper. It was difficult to achieve good hot-tack values with dispersion-coated paper. During testing, all the paper-based materials experience delamination and fibre tear, and its severity increases with the increasing material grammage. As plateau temperature is reached, the fibre delamination remains relatively constant. The ser-rated geometry of seal bar design plays a significant role in providing a satisfactory airtight seal, particularly around the pouch's layer jump. However, flat seal bar designs are not recommended for gas tight applications for paper-based materials.


| INTRODUCTION
In flexible packaging, industrial sealing applications are widely used.
For example, in vertical-form-fill-seal (VFFS) machines heat sealing method is commonly used. 1 The seal is achieved by compressing the inner side of the films under pressure and temperature using seal bars. 2 Most studies on the heat-sealing parameter optimization are regarding polyethylene-based materials.Airtight packages are essential for shielding the product from external damages and microbial and biochemical degradation. 3cently, the European Packaging Waste Directive (94/62/62EC) encouraged the reuse and recycling of packaging material as part of the contribution to EU's Green Deal and Circular Economy Action Plan by 2030. 4 Approximately 50% of paper-based materials are used by the packaging industry, and up to 70% of these materials are recycled. 5Extrusion-coated papers and paperboards are used in numerous consumer applications, such as food packages, medical devices and cosmetics. 6However, the recyclability of extrusioncoated paper materials is complicated; the materials require higher energy and create additional waste to separate the oil-based polymers from the paper material.Therefore, developing bio-based coatings is essential for minimizing environmental issues and reducing the coat weight. 7exible cellulose-based packages are of numerous types.Some of the previously studied materials in research include extrusioncoated with PE and dispersion-coated papers.Paper and paperboard packages possess good runnability, stiffness and ability to form the desired shape. 8Most coatings used for flexible paper and paperboard packages are low-density polyethene (LDPE) and polypropylene (PP).
Both of these coatings have several benefits; for example, LDPE acts as a barrier against water vapour, is easy to process, and offers excellent sealability with sufficient air tightness.The development of coatings highly depends on the polymer weight, grade and morphology.
Eventually, these critical features cause issues pertaining to the sealing of windows and seal strengths. 9The strength measurement of a seal is classified into two categories, hot-and cold-tack or commonly known as hot and cold seal strengths, respectively.Hot-tack is the measure of resistance to failure when the seal is melted; its strength is comparatively lower than that of cold-tack. 10In VFFS applications, the coating layer plays a critical role in withstanding the weight of the product and should be designed to avoid the seal separation in a short time.Minimizing the hot-tack issues in VFFS packaging can help maximize the output. 6In contrast, cold-tack, commonly known as the cold or seal strength, is defined as the force required to separate the cooled sealed layer a defined time after the sealing process.
For the VFFS packaging machine shown in Figure 1, the flexible film is generally supplied in the form of rolls from the manufacturer, where it is attached to the film handling system to produce pillow and block the bottom bags.The film is pulled by the transport belt over the rollers and forming shoulder; subsequently, it passes through the forming tube.Here, the film forms a cylindrical shape, where it is wrapped around itself with the vertical sealing bar.Then finally, horizontal seal bars create a horizontal seam to produce a bag for a product to be dropped from a dozer. 12th the global increase in efforts towards sustainable packaging, several research studies have focused on the sealability and tightness of the sealed seam with paper and paperboard materials.Most studies focused on laboratory scaled devices.For instance, Anderson et al 13 studied the heat sealability and barrier properties of dispersion-coated paper board by comparing two different coating layers containing NH 3 and NaOH.Heat-sealed samples exhibited fibre tears, thus indicating a cohesive failure mode during peel separation.However, neutralization with NaOH led to poor adhesion and weak seal strength.In another study, the heat sealability of aqueous polyolefin dispersion paper and paperboard materials was studied. 14The study reported that fibre tear was initiated in 3 s dwell time with 70 C sealing temperature and an improved dispersion-coated ethylene copolymer paper formula.
The description of satisfactory seal strength varies between different authors; however, based on Tuominen et al, satisfactory seal strength of paper-based materials is based on full fibre tear. 15The satisfactory seal strength for paper-based material is defined as the strength required to cause fibre tear; in this study, it was considered as the strength of the first fibre tear.Hauptmann et al 16 investigated the sealing behaviour of paper-based flexible packaging materials coated with acrylic layer and compared the results on a productionscale VFFS machine. 17 operating window.The seal strength of the paper-based material highly depends on their moisture content.Higher moisture content improves the hot-and cold-tack values. 17Furthermore, Hauptmann et al 17 investigated the airtightness of the pouches via the rhodamine test using the VFFS machine.They concluded that thermoplastic materials could produce gas tight packages, whereas the paper-based materials were not gas-tight within the selected operational sealing parameters; thus, they recommended the use of flexible membrane or seal bars to reduce the leakage rate in paper-based materials. 17her studies related to the sealing of sustainable materials, such as paperboard trays, have been conducted previously.Leminen et al 18 studied the effect of heat-sealing temperature on the sealing time and reported a clear improvement in gas tightness; however, obtaining a gas tight seal proved to be challenging.Furthermore, Leminen et al 19 demonstrated possibilities to improve the gas tightness of the paperbased package with additional sealing pressure.Although satisfactory modified atmosphere packaging (MAP) tightness and liquid tightness were achieved, the overall quality of the surface rim area was affected.These side effects were further proved through microscope imaging 20 ; the authors suggested that improving the sealing parameters, such as sealing temperature and pressure, had a positive effect on the heat-sealing process and maintained a reduced oxygen content inside the sealed trays if the quality of the seal was satisfactory. 21,22per-based materials have several advantageous properties, such as thermal stability.However, studies on the microscopic behaviour of heat sealed paper-based materials using various sealing profiles with the VFFS machine are lacking.The objective of this study was to evaluate and compare the seal strength and seal tightness of the oriented polypropylene layer with polyethylene laminate (OPP/PE), dispersion-coated paper material and PE-extrusion-coated paperbased material using different seal bars in the VFFS machine.To determine the production operating window, the seal strengths and the hot-and cold-tack were measured at a laboratory scale.The sealing parameters were optimized, and subsequently, pouches or pillow bags were made with the VFFS machine using different horizontal seal bar profiles.Finally, blue dye leak detection test was used to develop better visual understanding of the causes of leaks in the flexible packaging paper-based materials, and the sealed sections as well as layer jump area were examined with the scanning electron microscopy (SEM).

| Laboratory seal strengths
All the materials were sealed with RDM HSB-1 laboratory heat sealer (RDM Testing Equipment, Hertfordshire, United Kingdom) to evaluate the cold-tack using 25 mm wide flat seal bar to prepare the samples as per ASTM F88. 23The paper samples were precisely cut to 240 mm strips to have an equivalent surface pressure with hot-tack laboratory measurements.The two strips of materials were sealed such that the sealing layers faced each other.The sealing temperature ranged from 90 to 160 C, and the three fixed dwell times were 0.3, 0.5 and 1 s.
Sealing pressure is an important parameter for providing significant contact of the film surfaces.Merabtene et al 13 stated that pressure has no significant impact on the seal strength at various sealing temperatures and dwell times.Therefore, the sealing pressure was fixed at   Next, the sealed samples were allowed to age for 48 h in climatecontrolled environment at 23 C and 50% relative humidity and then cut into 25-mm-long strips for seal strength measurements.Aging is essential to maximize the heat seal strength stability. 23The seal strength was evaluated using a Universal Tensile Machine, Shimadzu AGS-X (Shimadzu, Kyoto, Japan) with a load cell of 1 kN ± 1%.The testing samples were prepared as per the standard ASTM F88.The sealed samples were attached and aligned at 25 mm from the gripper in the opposite directions.The samples were pretested at a constant rate (v) of 50 mm/min to remove any slack on the heat-sealed area.
Subsequently, the machine pulled at a constant rate of 300 mm/min until a 2% break was detected.
Hot-tack seal strength experiments were performed on a lab scale to pre-assess the operating window for manufacturing quality packaging.The hot-tack is determined on a lab sealer KOPP HCT 3200 with an integrated sealing device SGPE 3200 (Willi Kopp e. K. Verpackungssysteme, Reichenbach, Germany) (Figure 3) and was measured according to DIN 55571-2:2016-08 (Figure 3).Herein, 25-mm wide samples were cut and sealed with sealing layers facing each other.
Based on the results of the machine trials, the dwell time and sealing pressure were kept constant at 1 s and 0.

| Seal integrity and visual inspection
The leak-tightness of the pouches was visually inspected using the ASTM F3039 (2015) guidelines with some minor modifications.The coloured dye penetrant solution consisting of water and patent blue V sodium salt (0.05%) was used for the evaluation of the horizontal sealed area.The solution consists of 50 ml solution agent and was injected into the sealed area of the pouch for 5 s to assess the possible leaks in the channels.To eliminate the bias results, ten parallel pouch samples were tested.
Cross-section of the materials before and after heat-sealing, as well as surface images, were visually assessed through SEM (Hitachi SU3500 [Tokyo, Japan]).The cross-section of the heat-sealed samples was cut 30 mm equidistantly from the layer jump and the edge of the pouch.The micrographs of the cross-section were captured from the samples cast in acrylic resin (Struers ClaroCit).For the cross-section micrographs, the microscope was operated in variable pressure mode, and backscatter electron imaging in compositional mode (BSE-comp) was used.The acceleration voltage, pressure and working distance were 15 kV, 30 Pa and 10 mm, respectively.The method was chosen to provide contrast between different layers within the samples.The surfaces of the peeled samples were attached to carbon tape.Before imaging, the samples were sputter-coated (Au/Pd target).For surface images, secondary electron imaging (SE) was used.The acceleration voltage and working distance were set to 15 kV and 15 mm, respectively.

| RESULTS AND DISCUSSION
The hot-tack results obtained from laboratory-scaled analysis for each sample provided several recommended operation window to ensure material's resilience when filled with packaging product.Based on the seal strength analysis (cold-tack), pouches made with VFFS achieved a plateau sealing temperature and exhibited relatively stable seal strength at 130 C and 0.5 s.However, the severity of paper delamination increased with increasing paper grammage, thickness and sealing temperature.

| Laboratory seal strength results
The cold-tack results of the laboratory sealing tests are shown in

| Seal strength analysis of pouches made by VFFS
The operating window and optimum seal strength range for VFFS machine were determined based on the results obtained from crystallization of the seal. 25Therefore, all the microscopic evaluations were performed for the sealing temperature of 130 C at 0.5 s dwell time.
Compared with PE-coated paper materials, Disp.Paper 65 had substantially lower seal strength (approximately 50% less).Although both materials produced an intact seal with the serrated bar, speculatively, the coating layers plays a major role in the peel strengths.For instance, below a sealing temperature of 110 C and 0.5 s dwell time, minor cohesive failure was observed on all paper-based materials, regardless of the material type and seal bars.As the sealing temperature increased, the material began to tear and delaminate severely.
Merabtene et al 13 explained that the cause of this failure is attributed to a higher seal strength compared with the strength of the paper material.Based on the results, the increase in sealing temperature played a meaningful role in maximizing the formulation of intact seal.
Previously, Theller 24 Their paper evaluated the hot-and cold-tack behaviour of the OPP-and paper-based laminate films under different sealing parameters on a laboratory scale.Compared with the paperbased materials, OPP-based laminates were found to have a narrow F I G U R E 1 Schematic of VFFS packaging machine.The figure is modified from ref. 11

2. 1 |
Materials Three different flexible packaging materials were studied: thermoplastic reference material, dispersion-coated paper and PE-extrusioncoated paper-based material of two different thicknesses.The thermoplastic reference (Plastic Ref.) film consisted of the OPP layer with PE laminate; its total material thickness was 53 μm, comprising two layers: (1) OPP: 18 μm, and (2) ink/adhesive layer/PE: 35 μm.The dispersion-coated paper material (Disp.Paper 65) was heat sealable with 65 gsm dispersion-coated paper grade with material thickness of 66 μm; it consisted of 60 gsm of base paper and 5 μm of dispersion coating comprising a mixture of coating pigment and binder.The heat-sealability is achieved through the thermoplastic (thermosoftening) nature of the whole barrier structure.Two polymer-coated paper-based materials with different thicknesses and grammages were used.The thinner PE-coated paper-based material (Paper 70 + 15 PE) consisted of 70 gsm of base paper and 15 μm of PE laminate, whereas the thicker PE-coated paper-based material (Paper 90 + 30 PE) consisted of 90 gsm base paper and 30 μm PE laminate.These materials had a pigment coating at the back side for printability purposes.All paper-based materials were stored at a constant humidity chamber at 23 C and 50% RH.The moisture content of the material was measured using an Adams Equipment PMB 53 Moisture Analyzer (Oxford, CT, USA).The measured moisture F I G U R E 2 SEM microscopic cross-sectional images of materials: (A) Plastic Ref., (B) Disp.Paper 65, (C) Paper 70 + 15 PE and (D) Paper 90 + 30 PE. content for Disp.Paper 65, Paper 70 + 15 PE and Paper 90 + 30 PE was 5.92 ± 10%, 6.13 ± 10% and 8.91 ± 10%, respectively.The crosssectional view of the materials is provided in Figure 2.

0. 5 N
/mm 2 throughout this experiment.The cold-tack results were analysed to produce pillow bags for production test runs with the VFFS GKS-Compack CP350 Plus machine (GKS Packaging b.v., Eindhoven, Netherlands), as shown in Figure 3A.The VFFS machine has a surface temperature repeatability of 0.2 C. Herein, four seal bar profiles, shown in Figure 3B-E, were used in the VFFS machine.Then, the seal strength of the materials, leak tightness of the pouches and SEM micrographs of the seal cross sections are compared.The 11 mm serrated bar consist of flattened surface of 0.3 mm between each pitch.The serrated bar had a groove pitch, groove height and groove angle of 3.0 mm, 0.7 mm and 120 , respectively, as shown in Figure 3B.Other seal bar consisted of various dimension of flat width surfaces, including 11 mm, 4 + 3 mm and 4 mm, as shown in Figure 3C-E.The calculated surface pressures were based on the theoretical values from the forces exerted by the two pressure cylinders over the contact surface area geometry of the seal bar.Each pressure cylinder exerts a 982 N horizontally and 628 N for length seal at 0.5 N/mm 2 VFFS machine setting pressure.The 11 mm serrated bar consists of the actual contact surface width of 13.6 mm.Therefore, according to the theoretical calculations, the 11 mm serrated bar led to relatively lower surface pressure compared with other flat bars owing to the geometrical wave form.However, speculatively, the 120 groove angle provides a significantly higher surface pressure due to minimal contact area at the tip of the serrated bar.Table 1 lists these values without considering the energy losses caused within the pressure cylinders.

F I G U R E 3
Seal bar profiles used for VFFS GKS-Compack CP350 Plus.T A B L E 1 Calculated surface pressure for various seal bar profiles used in the GKS VFFS machine.GKS VFFS length seal GKS VFFS horizontal seal bars Seal bar name Longitudinal length sealer 11 mm serrated bar 11 mm flat bar 4 + 3 mm flat bar 4 mm flat bar Pressure (N/mm 5 N/mm 2 , respectively.The sealing temperature ranged between 80 and 140 C for all the four materials.The waiting time before measuring the opening force for hot-tack was set by the device to 0.24 s.The measurements were executed with the device's maximum pull-off speed of 12 m/min at the tear roll.Therefore, due to the hot-tack measurement principle (Figure 4, middle) with a fixed clamp opposite the tear roll, the corresponding tear speed at the sealed seam was 6 m/min.To consider the different bar designs for the machine trails, two different seal bar patterns were used within the hot-tack measurements: 10-mm wide flat bars, and a 10-mm wide serrated pattern with a groove pitch, groove height and groove angle of 2.5 mm, 0.8 mm and 65 , respectively (Figure 4, right).The recorded values represent the maximum peel force occurring over the opening path.

Figure 5 .
Figure 5. Evidently, the Plastic Ref. material exhibited an increase in the linear seal strength between the sealing temperatures of 110 to 130 C, whereas it remained stable until 140 C; at this stage (140 C), the Plastic Ref. material reached the plateau temperature. 24Above 140 C, the seam area began to distort and coarsen due to high sealing laboratory scale hot-and cold-tack tests respectively.For the experiments, the selected heat-sealing temperature ranged from 100 to 150 C, with dwell times of 0.3, 0.5 and 1 s.The thermoplastic flexible materials were found to have an outstanding seal and airtightness compared with the paper-based materials.As shown in Figure 7, the Plastic Ref. material had a weak seal, with a sealing temperature and dwell time of approximately 110 C and 0.3 s, respectively, regardless of the seal bar profiles.At this stage, the seam was weak for production application owing to insufficient diffusion of polymer molecules to create intact seal.However, for sealing temperatures above 110 , the Plastic Ref. material was air-and leak-tight.A sharper increase in the seal strength was observed between sealing temperatures 110 and 120 C with a serrated bar profile until it reached approximately 50 N/25 mm ± 10% for 0.5 s dwell time.The flat-based seal bar profiles had a linear seal strength growth at temperatures up to 120 C, and exhibited a plateau in the strength for sealing temperatures between 130 and 140 C.A significant drop in the seal strength F I G U R E 6 Hot-tack temperature diagrams for comparison of seal bar pattern at different temperatures.F I G U R E 7 Cold seal strength test of thermoplastic reference material using VFFS machine.was observed after 140 C, particularly at 1 s dwell time, to approximately 20 N/25 mm ± 10% owing to the shrinkages of the seal.This leads to the conclusion that thermoplastic material can provide better tight seal with shorter dwell times.At temperatures above 120 C and 0.5 s dwell time, all the pouches were observed to be air and leak tight, regardless of the type of seal bar profiles.The coarsening effect on the OPP/PE layer developed an intact and leakproof seal above 120 C when tested with water-based dye penetrant solution.Although the results are not shown, based on the microscopic evaluation, proper interdiffusion and melt flow of PE laminate were confirmed.On average, the sealing layer of Plastic Ref. material was five times stronger than that of the dispersion-coated paper and four times stronger than that of PE-coated paper at 130 C and 0.5 s.The seal strengths of the paper-based materials were compared along various seal bar profiles and parameters, as shown in Figure 8.The peel strengths of the paper-based materials differed depending on the sealing parameters, material type, thickness and seal bar profiles.Therefore, these parameters influence the strength and peelability of the seal, whether it results in seal strength or coating strength.At 0.3 s dwell time, the paper-based material had difficulties in having intact seal below sealing temperatures of 130 C. Above 0.5 s dwell time, the majority of the seal bar profiles recorded the highest seal strength values at the sealing temperatures of 130 and 140 C and remained constant with minor fluctuations.At this stage, the laminate achieved the highest possible molecular chain entanglement and confirmed that the effect of dwell time on seal strength is constant when plateau temperature is reached for low density polyethylene films.Similar phenomenon were observed with PE-coated paper and dispersion-coated flexible materials at sealing temperatures above 130 C and 0.5 s dwell time.The dwell time should be adequate to ensure that the heat transfer is sufficient for melting the sealant material.According to the heat transfer theorem, the seal strength is influenced proportionally by the dwell time; however, an exception was observed with Paper 90 + 30 PE. Speculatively, Paper 90 + 30 PE materials did not reach the plateau temperature even above 150 C sealing temperature and 1 s F I G U R E 8 Cold seal strength test of PE-coated paper-based materials using the VFFS machine.
Figure 9 parts (D) and (F), it is possible to conclude that the larger the thickness of the paper material, the larger the voids near the layer jump area.The Disp.Paper 65 had an intact seal in the layer jump area; however, some major leaks along the sides of layer jump were observed.Additionally, compared with the PE-coated paper, Disp.Paper 65 had leaks on the surface of the pillow bag, which were caused by the sharp bend of the forming shoulder.Hauptmann et al 18 recommended the use of flexible sealing membrane on one side of seal bar to enable an elastic feature when in contact with a rigid bar on the other side.This resulted in a significant reduction in leakage rate.Overall, the Plastic Ref. material exhibited adequate leak-proofness and airtightness above 120 C and 0.5 s, even with flat seal bar profiles.From the failure mode analysis, the PE-coated papers and dispersion-coated paper peeled similarly during the seal strength test.Based on the visual inspection, at lower sealing temperatures below 120 C, the seal interface had no major damage.The seal strength was among the lowest because the sealing temperature was not sufficient

F I G U R E 1 0
Comparison of leak test results between 11 mm serrated and flat bar with paper-based material at 130 C and 0.5 s. (A) Disp.Paper 65 using 11 mm serrated bar.(B) Disp.Paper 65 using 11 mm flat bar.(C) Paper 70 + 15 PE using 11 mm serrated bar.(D) Paper 70 + 15 PE using 11 mm flat bar.(E) Paper 90 + 30 PE using 11 mm serrated bar.(F) Paper 90 + 30 PE using 11 mm flat bar.F I G U R E 1 1 Fibre tears of paper-based materials using serrated bar profile at 130 C and 0.5 s.The peeled-off fibres from Figure 11 were inspected using the SEM from above, as shown in Figure 12.The first part of the micrographs presents the SEM images of the coating layer before heat sealing is applied, as shown in Figure 12A1,B1,C1.The Disp.Paper 65 had some minor holes and layers of fibres on the surface of the paper, as shown in Figure 12A1.Practically, with the VFFS machine, Disp.Paper 65 had difficulties producing an intact seal with flat seal bars owing to the possible lack of pressure.Compared with the PE-coated paper materials, the Disp.Paper 65 had the weakest seal strength, which was proven based on the microscopic evaluation.In Figure 12A1, some fibre layers and holes can be observed on the upper coating layer, which proves that the dispersion coating on the coating side is lacking and the coating layer is inconsistent when observed through cross-sectional view, as shown in Figure 2B.The dispersion coatings had a thicknesses of 5-12 μm.The PE-extrusion-coated paper materials had a surface texture created by the chilling roll in the extrusion coating process presented in Figure 12.The density of the coating structure was larger on Paper 90 + 30 PE (Figure 12C1) compared with Paper 70 + 15 PE (Figure 12B1).
Figure 12A2,B2,C2 present the heat sealed samples at 130 C and 0.5 s with serrated seal bar.The results confirmed that Paper 90 + 30 PE (Figure 12C2) had thicker delaminated fibres compared with Paper 70 + 15 PE (Figure 12B2), and Disp.Paper 65 (Figure 12A2).It is possible to justify that the saturation of the pouches led to higher seal strengths, due to which Paper 90 + 30 PE achieved better seal strengths.4 | CONCLUSION The study evaluated the seal strength for various flexible packaging materials such as Plastic Ref. or oriented polypropylene layer with polyethylene laminate (OPP/PE), dispersion-coated paper material and PE-extrusion coated paper-based material using different seal bars in the VFFS machine.Furthermore, the effect of processing parameters on the seal tightness of the pouch packages along with various seal bar profiles were compared on a microscopic level.The Plastic Ref. and paper-based materials behaved significantly different to each other.On average, at 130 C and 0.5 s dwell time, the seal strength of the Plastic Ref. material was four times stronger than the PE-coated paper and five times stronger than dispersioncoated paper.The Plastic Ref. material began to shrink and coarsen at F I G U R E 1 2 Top view of before and after fibre tears for paper-based materials using serrated bar profile at 130 C and 0.5 s.140 C and above.This coarsening effect allowed the material to have an intact leakproof seal when tested with the dye-penetrant solution.Based on the microscopic evaluation, proper interdiffusion of PE laminate was confirmed; however, producing such packages with coarsened and distorted sealing layer is not practically beneficial as it reduces product's quality appearances and customer satisfaction.The PE-and dispersion-coated paper materials had the ability to withstand higher sealing temperature ranges and wider operating window with no major effects on the sealing layer as compared to Plastic Ref. material.However, it was quite difficult to achieve good hot-tack values with dispersion-coated samples.Therefore, in applications where sufficient hot-track is needed, dispersion-coated paper can be a difficult choice of use.For cold-tack, the increase in sealing temperature maximized the formulation of an intact seal.Above 130 C sealing temperature and 0.5 s dwell time, the paper materials reached plateau sealing temperature and exhibited relatively stable seal strength.During the seal strength test, all paper materials experienced full delamination and fibre tears when sealed above 130 C sealing temperature.Based on the SEM micrographs, the severity of paper delamination during peeling increased with increasing paper grammage, thickness and sealing temperature.Unlike the flat seal bar profiles, the 11 mm serrated bar had the ability to provide airtight and leakproof pouches, particularly at the layer jump area.An inspection with the dye penetrant solution revealed that the 120 groove angle from serrated bar created localized shear stress and resistance to leak.SEM cross-sectional micrographs proved that flat sealing bar profiles created voids and gaps, particularly around the layer jump area, which was not observed in the case of 11 mm serrated seal bar.In comparison to PE-coated paper, the Disp.Paper 65 had several surface leaks, caused owing to the folding of paper material over the forming shoulder.This research determined the overall behaviour of the materials in the VFFS process with different seal bars; additionally, it concludes that functional pouch packages can be produced from the materials as long as the bars and operating parameters are adjusted correctly.The sealing temperature played a significant role in maximizing the seal strength and tightness of the paper-based materials.Furthermore, we recommend the use of serrated bars on achieving sufficient airtight and leakproof pouched with the VFFS machine.