Chapter 7 Result and discussions
7.1 Surface Free energy of Substrates
7.1.2 Dyne Pen Test
7.1.2 Dyne Pen Test
The methodology is as discussed in the chapter 6. The dyne pen or marker test was conducted both on surfaces without treatment and surfaces with flame treatment, on both the substrate surfaces; PP+LGF and PP+T. Technological markers with different standard values of dyne/mm. These standards indicate the surface free energy of the surfaces. For good adhesion properties of the substrate surfaces, the critical surface
energy had to be above 38 mN/m, when the substrates were tested with the technological markers, the results obtained from the drop test were confirmed as the technological marker of number 38 and number 40 did not form any droplets on the surface of the substrates (see figure 33).
Figure 33 Dyne Pen test (Left) PP+T; (Right) PP+LGF
7.2 Differential Scanning Calorimetry (DSC) Analysis DSC Analysis for adhesive: Teroson PU 8599 - HENKEL Plot 1: First heating phase
Plot 1 First heating phase
The above plot 1 is the 1st heating phase of the adhesive - Teroson PU 8599. The heating phase was constant with a rate of 5oC/min.
The atmosphere used during this test was an inert nitrogen atmosphere. The weight of the adhesive in the pot was 19.250 mg.
There is a distinctive peak, an endothermic reaction seen between the temperature ranges from 35.60oC to 48.16oC. The top of the peak is at 44.41oC which indicates the region of polymerization or melting of the adhesive.
Plot 2: Different heating rates
Plot 2 Different heating rates
The above plot 2 is the complete heating phase of the adhesive – Teroson PU 8599. The heating phase was constant with an increased heating rate of 10oC/min in an inert nitrogen atmosphere. The weight of the adhesive in the pot was 14.04 mg.
The endothermic region can be seen in the temperature ranges from 34.06oC to 54.16oC and the distinctive peak is at 43.89oC.
This test at a different heating rate was conducted to verify the original results, that revealed an endothermic reaction, polymerization or melting in the temperature ranges between 34oC to 55oC.
Plot 3: Ten cycles of consecutive heating and cooling phases
Plot 3 Ten cycles of consecutive heating and cooling phases
The above plot 3 shows ten repetitive cycles of heating and consecutive cooling of the adhesive – Teroson PU 8599. The heating and cooling rates were maintained at 5oC/min with an inert nitrogen atmosphere. The weight of the adhesive in the pot was 35.890 mg. The ten cycles were measured in the time span of approximately 320 minutes. There is a distinctive endothermic peak in all the heating cycles, which would indicate a repetitive process that indicates some structural changes (melting) whereas, in the cooling cycles, no such peaks are formed. This indicates that there is no crystallisation process (displayed by typical exothermic peak), and exothermic reaction occurring in the cooling phase.
Plot 4: Oxidizing atmosphere
Plot 4 Oxidizing atmosphere
The above plot 4 shows ten heating and cooling cycles of the adhesive – Teroson PU 8599. The heating and cooling rates were maintained at 5oC/min. The weight of the adhesive in the pot was 12.690 mg. The inert nitrogen atmosphere was changed to an oxidizing atmosphere, hence there is a change in the peak. A distinctive peak can be found in the first few heating cycles, which diminishes gradually after ever consecutive cycle, indicating that the adhesive is reacting with the oxidizing atmosphere. There are no peaks formed in the cooling phase at all.
Plot 5: Comparison between nitrogen and oxidizing atmospheres
Plot 5 Comparison between nitrogen and oxidizing atmospheres
The above plot 5 shows the heating phase in different cycles, first, second and tenth cycle respectively, when subjected to nitrogen and oxidizing atmospheres. The distinctive peak during the heating phase, indicating an endothermic reaction gradually decreases when exposed to an oxidizing atmosphere. The gradually decrease can be seen in the consecutive cycles from the first cycle until the tenth cycle whereas, when the adhesive is exposed to an inert nitrogen atmosphere, this reduction in peak is minimal, showing repetitive endothermic reactions in the heating cycle from the first cycle until the tenth cycle. These diagrams predicate not only structural changes, but also some irreversible processes based on interactions with standard atmosphere.
DSC Analysis for adhesive: TDS EFBOND DA 174 - EFTEC Plot 6: First heating phase
Plot 6 First heating phase
The above plot 6 shows the first heating phase of the adhesive – EFBOND DA 174. The heating rate was maintained at 5oC/min.
The weight in the pot was 13.320 mg and the atmosphere used for the testing was an inert nitrogen atmosphere. An endothermic reaction was seen in the temperature ranges from 33.38oC to 58.28oC and a characteristic peak can be seen at 51.45oC, which indicates polymerization or melting of the adhesive which is repetitive in all cycles.
Plot 7: First cooling phase
Plot 7 First cooling phase
The above plot 7 shows the first cooling phase of the adhesive – EFBOND DA 174. The cooling rate was maintained at 5oC/min with an inert nitrogen atmosphere. There is an exothermic reaction region between the temperature ranges 37.34oC to 24.13oC during cooling, with a distinctive peak at the temperature of 31.38oC. This peak indicates the crystallisation of the adhesive during cooling which is repetitive in all cycles.
Plot 8: Comparison between the adhesives – Teroson PU8599 and EFBOND DA 174
Plot 8 Comparison between the adhesives
When the two adhesives are compared with each other for consecutive ten cycles, there are characteristic peaks in the heating phase for both the adhesives whereas, the characteristic peaks during cooling phase can be seen only in the adhesive EFBOND DA 174.
7.3 Temperature Profile Analysis
The methodology of the test is as discussed in chapter 6.2.3. The results from the tests are as follows;
Temperature profile analysis: Core temperature in the cartridge
Plot 9 Core temperature in the cartridge – Henkel – Teroson PU 8599
The above plot 9 shows the profile of temperature changes in the core region of the cartridge for the adhesive – Teroson PU 8599.
This experiment was conducted to optimize the temperature of the oven and to understand the heat transfer properties of the adhesive. In the plot (x axis – time in minutes; y axis – temperature in deg. Celsius), blue line denotes the temperature in the oven and the orange line denotes the temperature in the core region of the cartridge. The temperature in the oven was set so that there is a gradual increase in the temperature until 65oC, which was the higher limit of application temperature for the adhesive and to maintain it constant. The cartridges were placed in the oven simultaneously and the temperature changes were recorded for over 180 minutes (3 hours). As the temperature in the oven increased gradually, the temperature of the core of the cartridge increased but at a slower rate. The temperature in the oven was stabilized at 65oC after an hour (60 minutes), but the temperature in the core of the cartridge took more than 2 hours (~160 minutes) to stabilize at 65oC.
Plot 10 Core temperature in the cartridge – Eftec –Efbond DA 174
The above plot 10 shows the changes in temperature in the core of the cartridge of the adhesive – Efbond DA 194. This experiment was conducted to optimize the temperature of the oven and to understand the heat transfer properties of the adhesive. In the plot (x axis – time in minutes; y axis – temperature in deg. Celsius), the red curve indicates the change of temperature in the oven and the yellow curve denotes the changes of temperature in the core of the adhesive cartridge. The temperature in the oven was set to the higher limit of application temperature of the adhesive – 70oC. The cartridges were placed in the oven simultaneously and the temperature changes were recorded for a period of 160 minutes (2.5 hours), until the temperature in the core of the cartridges was stabilized. The temperature in the core of the cartridge increased in a slower rate than compared to the rise of temperature in the oven. It was observed that, the temperature in the core of the cartridge was stabilized after approximately 2.5 hours (160 minutes).
Temperature profile analysis: Application Temperature – 65oC for adhesive – Teroson PU 8599
Plot 11Comparison of different temperature profiles for different joint thicknesses
The above plot 11 (x axis – time in seconds; y axis – temperature in deg. Celsius) shows the temperature profiles of the adhesive – Teroson PU 8599 at the application temperature 65oC with different thicknesses of the adhesive joint. The orange, blue and yellow curves denotes the thickness of adhesive joint being 5mm, 3mm and 1mm respectively. The temperature profiles are recorded from the time of application of adhesive until it stabilizes to the room temperature. This experiment was conducted to check if the substrates influence the heat removal properties of the adhesive.
The substrates used for this experiment were polypropylene with long glass fibres (PP+LGF). The heat removal from the adhesive joint increased with decrease in the thickness of the joint, whereas the substrates did not affect this property. There was a gradual decrease in heat from the application temperature to the room temperature. The peaks seen on the plot is due to the application of weight on the adhesive joint during the initial stages which creates friction between the different layers of the adhesives
0
Temperature profile analysis – Application temperature – 55oC for adhesive – Teroson PU 8599
Plot 12Comparison of different temperature profiles for different joint thicknesses
The above plot 12 (x axis – time in seconds; y axis – temperature in deg. Celsius) shows the temperature profiles for the adhesive Teroson PU 8599 at the application temperature 55oC for different thicknesses of the adhesive joint. The orange, grey and yellow curves denotes different thicknesses of the adhesive joint being 5mm, 3mm and 1mm respectively. The substrates used during this experiment were polypropylene with talcum (PP+T). There is a gradual decrease in the temperature of the adhesive joint with time and it is faster with decrease in the thickness of the joint. The substrates did not affect the property of heat removal of the adhesives. The peaks seen in the initial stages of the curve are due to the pressure applied by the weight kept on the joint, which creates friction between the different layers of the adhesives.
Temperature profile analysis – Application temperature – 60oC for adhesive – Efbond DA 174
Plot 13 Comparison of different temperature profiles for different joint thicknesses
The above plot 13 (x axis – time in minutes; y axis – temperature in deg. Celsius) shows the variation in temperature profiles for different thickness; 1mm (blue), 3mm (orange) and 5mm (grey) respectively. For the application temperature of 60oC, which was the lower limit of recommendation for the adhesive Efbond DA 174, distinctive peaks are seen in the plot (x axis – time in minutes; y axis – temperature in deg. Celsius). These peaks denote the time of application of adhesive on the substrate and time of application of load on the joint. There is a gradual decrease in temperature seen in all three cases. The process of crystallisation seen during DSC analysis (Plot 7) is also observed in the above plot 13. From the range of 45oC to 35oC, there is faster cooling of the adhesive, which indicated the crystallisation process.
Temperature profile analysis – Application temperature – 70oC for adhesive – Efbond DA 174
Plot 14 Comparison of different temperature profiles for different joint thicknesses
The above plot 14 (x axis – time in minutes; y axis – temperature in deg. Celsius) shows the temperature profiles for the higher limit of application temperature (70oC) for the adhesive Efbond DA 174.
The blue, orange and grey curves indicate the temperature profile during the cooling period of the adhesive. The peaks seen during the initial stages of cooling on the plot denote the application of adhesive on the substrate and the application of load on the adhesive joint. The crystallisation process can be seen in the range of 45oC to 38oC during cooling, as there is a rapid cooling of the adhesive joint.
7.4 Shear test (Gangel Test)
The test was conducted on both substrates PP+LGF and PP+T;
with different waiting times and different thickness of adhesive bonds. The methodology is as discussed in the previous chapter.
For each thickness, the experiment was conducted for a series of 5 times and the result is the average of the values obtained by these trials. The tests were conducted for the lower and higher limit of recommended application temperatures for the adhesives. The plot of thickness versus time for failure of adhesive joint is as follows;
Plot 1: Application temperature – 55oC for Teroson PU 8599
Plot 15 Comparison of time of failure for different thicknesses
The above column chart 15 (x axis – thickness of adhesive joint in millimetres; y axis – time of failure in seconds) shows the times for the failure of the joint with respect to the waiting times and thickness of the joint. The blue, orange and grey bars represent the time of failure for waiting time of 1minute, 3minutes and 5 minutes for thickness 1mm, 3mm and 5mm respectively. The adhesive joints occurred failure as the thickness of joints increased and the time of failure increased as the waiting time after application of adhesive increased. To explain, consider the thickness of joint as 1mm; the time of failure of joint increases as the waiting time increases. Now considering all the three thicknesses, the totally failure time decreases exponentially as the thickness of joints increase. It can be concluded that for the application temperature of 55oC, thickness of 1mm is optimum with highest efficiency of adhesive joint.
Table 7 Modified shear test (Gangel test) - measured and calculated values
From the equation to calculate apparent viscosity (chapter 5.2), these values of viscosity are computed.
𝜂 =
2𝑚𝑔ℎ𝑡𝐿2𝑤 (Eq. 7) Where, η = apparent viscosity (Pa-s); m = 252.80g = 0.2528 Kg; g= 9.81 m/s2; h = thickness (0.001m, 0.003m and 0.005m); t = time in seconds (s); L = 0.015m and w = 0.025m.
From the table 7, it is observed that the apparent viscosity has a wide range and it is maximum for the thickness of 3mm with a waiting period of 5 minutes for the application temperature of 55oC.
Plot 2: Application temperature – 65oC for Teroson PU 8599
Plot 16 Comparison of time of failure for different joint thicknesses
The above column chart 16 (x axis – thickness of adhesive joint in millimetres; y axis – time of failure in seconds) shows the times for failure of the adhesive joint with respect to the waiting times and thickness of joints. The blue, orange and grey bars denote the time of failure for the waiting time of 1 minute, 3 minutes and 5 minutes for thicknesses 1mm, 3mm and 5mm respectively. There was an increase in strength of adhesive bond as the thickness increased from 1mm to 3mm and it reduced rapidly when the thickness increased to 5mm. The strength of the bond increased as the waiting time after application of adhesive increased. To explain, considering the thickness as 3mm, the time of failure of joint increase when the waiting time increased. Now considering all the thicknesses of joints, it can be concluded that the optimum thickness for the application temperature of 65oC is 3mm for maximum strength of adhesive bond.
Table 8 Modified shear test (Gangel test) - measured and calculated values
From the table 8, it can be observed that the apparent viscosity increases with increase in waiting time and the optimum thickness for maximum viscosity was found out to be for 3mm with waiting time of 5 minutes for the application temperature of 65oC.
Plot 3: Application temperature – 60oC for Efbond DA 174
Plot 17 Comparison of time of failure for different joint thicknesses
The above column chart 17 (x axis – thickness of adhesive joint in millimetres; y axis – time of failure in seconds) represents the time of failure of adhesive joints with respect to different thickness of
joint and waiting times for the adhesive Efbond DA 174. The blue, orange, grey, yellow and green bars represent the time of failure for the adhesive joints for the thickness 1mm, 3mm and 5mm; and for waiting times 1minute, 2 minutes, 3 minutes, 4 minutes and 5 minutes respectively. The time of waiting is varied by 1 minute as there was a huge change in the strength of bond within 60 seconds increase in waiting time. The bars which exceed the time of failure 3 seconds (y-axis); extend more than 180 seconds (3 minutes) and did not experience failure of joint. For the realization of the plot, these bars are shortened to explain in detail the other time of failure for different waiting periods and thicknesses. For the application temperature of 60oC, being the lower limit of the adhesive for application, it can be concluded that for 1mm of thickness and for a waiting time of more than 2 minutes there is a huge increase in the strength of the adhesive, which can be seen from the chart. As the thickness of the adhesive joint increases the strength of the joint decreases with reduction in waiting time.
Table 9 Modified shear test (Gangel test) - measured and calculated values
From the table 9, it is seen that the apparent viscosity increases significantly as there is an increase in the waiting time after the application of adhesive. It can also be seen that apparent viscosity cannot be determined (high values), as the adhesive bond was not broken during several tests (time of failure exceeding 3 minutes).
The apparent viscosity of the adhesive increases rapidly within the
application temperature of 60oC and waiting time of more than a minute are the optimum parameters for efficient bonding.
Plot 4: Application temperature – 70oC for Efbond DA 174
Plot 18 Comparison of time of failure for different joint thicknesses
The above column chart 18 (x axis – thickness of adhesive joint in millimetres; y axis – time of failure in seconds) shows the representation of time of failures for the different thickness of adhesive joints for different waiting periods. The blue, orange, grey, yellow and green bars represent the time of failure for the waiting period of 1 minute, 2 minutes, 3 minutes, 4 minutes and 5 minutes for thicknesses 1mm, 3mm and 5mm respectively. The time of waiting is varied by 1 minute as there was a huge change in the strength of bond within 60 seconds increase in waiting time.
The bars which exceed the time of failure more than 3 seconds (y-axis), did not experience failure of joint. For the realization of the chart, it is shortened for better understanding of other failure times.
As the thickness of the bond increased, the strength of the bond decreased for the application temperature of 70oC. For this application temperature of the adhesive, it can be concluded that the thickness of 1mm and for a waiting period of more than 60 seconds is optimum for good adhesive strength of the bond.
Table 10 Modified shear test (Gangel test) - measured and calculated values
From the table 10, the effect of application temperature changes comparing the lower and higher limits of recommended application temperatures. At 70oC with a thickness of 3mm, the strength of adhesive bond is not satisfactory (when compared with the thickness of 1mm – maximum strength is achieved after a waiting time of more than 2 minutes). The optimum parameters for efficient bonding are 1mm of adhesive thickness and for a waiting time of more than a minutes.
For the adhesive Efbond DA 174, with the change of waiting time and the rapid increase in the strength of the joint can be explained by the crystallisation process which was shown in the DSC analysis (Chapter 7.2). The strength of bond increases rapidly, when the temperature within the joint dropped under approximately 38oC, which could also explain the high precision tack effect of the adhesive.