## 2 State-of-the-Art Methodology  
### The Need of Revised Standard  
A practical experiment on T-peel test measurement is done on the flexible packaging film as a method for measuring the peel strength of an adhesive. Peel tests are most commonly used to evaluate laminated film or bonded adhesives. Thus, a peel test is preferred when working with multiple film packaging in this study, namely polyethylene (PET), polyamide, aluminum (Al), cast polypropylene (CPP), and bonded with adhesives. There are four main types of peel tests: 90\({}^{\circ}\) peel, 180\({}^{\circ}\) peel, T-peel, and climbing drum peel. The 90\({}^{\circ}\) peel test is suitable for a flexible adhesive material that is adhered to a more rigid substrate. The 180\({}^{\circ}\) peel test is best used when the flexible substrate can be bent back by 180\({}^{\circ}\). The T-peel test is best used when both adhesive and adhered are similar or flexible. Therefore, the T-peel test is the most suitable peel test to measure the peel strength of this material. The T-peel test apparatus as described in Figure 1 is a newly revised apparatus derived from current standard JISK6854-3 (2008) [27] and American Society of Testing and Materials; ASTM 1876-08 [28] to fulfill industrial requirement. The apparatus in Figure 1 is used to develop the optimum condition for flexible film.  
As shown in Figure 2b, in previous standardized method JISK 6854-3 (2008) [27] and American Society of Testing and Materials; ASTM 1876-08 [28], the peel angle is not maintained at 90\({}^{\circ}\) for flexible film, thus it leads to a big variation in peel strength during peeling. Therefore, the new testing apparatus is developed shown in Figure 2c to encounter the variation problem in flexible film due to peel angle instability.  
The drum rotates by the spur gear according to the peel speed as a string is attached at a fixed point and tied on the drum's pulley as shown in Figure 3 schematic diagram. As the drum rotates according to the peel speed, the migration stage is being moved back and forth to the initial state. Angle adjuster is used to change the peel angle according to several setting from 0\({}^{\circ}\) to 180\({}^{\circ}\). The flexible film adhesive is attached to the drum. A weight (paper clip) was fixed on the free end of the film to  
Figure 1: T-peel test apparatus set-up (1 cm photo:5 cm actual).  
Figure 2: (**a**) Standardized T-peel test method Japanese Industrial Standard (JIS) [27] and American Society of Testing and Materials (ASTM) [28] and (**b**) Failure of flexible film specimen to stabilize the peel angle, (**c**) the new testing apparatus for T-peel test as shown in Figure 1.  
keep the specimen in T-shape. The drum rotates according to peel speed as a string is attached at a fixed point and tied on the drum's pulley. Peel speed and peeling distance can be changed according to apparatus specifications. A parallel spring is pulled by pulley wire along the peeling process. Three spring thicknesses were used for this study: 0.3 mm, 0.4 mm, and 0.5 mm. During the peeling process, displacement is triggered by a parallel spring caused by peel strength and detected by a laser sensor. This apparatus can obtain a wide range of peel strength measurements by changing the spring thickness.  
Peel strength increased proportionally to specimen width as shown in Figure 4. Higher strength is needed to peel away the adherend from the adhesive as the specimen width increases.