Report On Dynamic Mechanical Testing Of Polymers Engineering Essay

Report On Dynamic Mechanical Testing Of Polymers Engineering Essay

In this study, HIPS and pure PS were tested by utilizing DMA at the same temperature scope from 20 to 120. Both 1 Hz and 10 Hz were used as the testing frequence and it was found that higher proving frequence gave higher glass passage value. Around the glass passage temperatureand E ” had a maximal value. However for E ‘ , it began to diminish around Tg. The experiment besides showed that as HIPS has rubber atoms in it, it exhibit lower glass passage temperature and modulus. In the study, appraisal was besides given based on mention that if proving was from -100 to 25, passages may be observed in curve. Tg for gum elastic atoms may besides demo a extremum at this temperature scope for HIPS.

Dynamic mechanical analysis ( DMA ) is a sort of thermoanalysis which can be used to analyze the physical belongingss of stuffs. By using an hovering force on the sample, the tried stuffs with different physical belongingss will hold different response. The response of the stuff can be recorded such as lose energy, elastic response, stage lagging and so on. [ 1 ] This is a really utile technique for polymer analysis. As they are recognized as viscoelastic stuffs, the lose energy, stage lagging can stand for the stage alterations, temperature passage every bit good as many other belongingss. By and large there are two proving method: free oscillations and forced oscillation. For free oscillations, the force will be applied and so removed and let the sample oscillate by itself. For forced oscillation, the force will be applied through the whole experiment continuously. [ 2 ]

One of the most of import applications for DMA is to observe assorted passages in polymer. In the DMA testing, the sample is tested under a scope of temperature with a changeless frequence ( or changeless temperature with frequence altering ) . The Young ‘s modulus will alter during the testing scope which can stand for the glass passage temperature, crystallinity every bit good as altering in crosslinking denseness. [ 1 ] From the DMA consequence, some molecular information can besides be got. Through the Doi-Edwards theory, the loss modulus and the storage modulus is related to the molecular weight and molecular distribution. [ 1 ] Most of the DMA machine presents can make creep-recovery testing. The DMA testing environment is besides mutable. One of the typical environments which are normally used is UV. UV can be used as an environment to speed up the ripening of polymer in order to observe the mechanical belongingss alterations during aging. [ 2 ]

EXPERIMENTAL

Both PS and HIPS samples were tested by TA 2000 Dynamic Mechanical Analyzer with a temperature scope of 20 to 120 grade centigrade. The breadth of each sample was around 10mm and the distance between jaws were set at 30mm.

First the sample was placed in the machine and so the DMA machine was closed. The proving status was input into the machine so. The warming rate was set as 5/min to 120. PS and HIPS were tested both at 1 Hz and 10 Hz and the E ‘ , E ” and Tani?¤ hints of PS and HIPS were got straight by the computing machine.

Consequence

Degree centigrades: UsersAdministratorDesktopPS.jpg

Figure 1: The DMA consequence of PS including the storage modulus, loss modulus and Tan Delta.

Degree centigrades: UsersAdministratorDesktopHIPS.jpg

Figure 2: The DMA consequence of HIPS including the storage modulus, loss modulus and Tan Delta.

Discussion

Loss modulus E ” and influence of frequence on it

Both figure 1 and 2 shows that during the testing temperature scope, the loss modulus has a peak value. After that, it decreased and attack to zero. Normally the temperature where the loss modulus reaches the peak value, is defined as the glass passage temperature [ 3 ] . The loss modulus and storage modulus are defined as following two equations

Storage modulus

Loss modulus

From this it can be known that is the minus derivate of. So will demo a upper limit when have the fastest lessening. When temperature was low, the gesture of the concatenation section was small and can non response the outer force and internal equilibrium can non be reached, hence, it chiefly show mean strain and the modulus is high and the swill of the little. As temperature increased, the gesture of the polymer concatenation section besides increased. As the section gesture began to response the applied force and the storage modulus began to diminish ( slope addition ) . More energy was dissipated during this process and the loss modulus increased. When the section gestures can rightly response the applied force frequence, the loss modulus reached the maximal value and the storage has the highest decreasing. After that, as the section gesture was faster than the frequence of the applied strain, it will make equilibrium internally instead than externally which is called quasi-static. So the alteration of storage modulus began to diminish and the loss modulus besides decreased. [ 4 ]

Table 1: The glass passage temperature of PS and HIPS samples under different frequence.

Materials

Frequency

1Hz

PS

111.63

Hip

97.33

The consequences besides show that higher proving frequence gave a higher glass passage temperature. This is because that when the frequence is higher, more moving ability of the polymer concatenation section is needed to catch up with the frequence of applied strain and make the maximal loss modulus. As better traveling ability needs a higher temperature, the Tg tested will be higher when the frequence is higher.

Another account is that when temperature is much lower than the glass passage temperature, the section and side group of polymer ironss are frozen. So there is no gesture in the ironss. The loss modulus is chiefly caused by the clash between the polymer ironss and it does n’t alter. When temperature is nearing the glass passage temperature, some of the side groups begin to travel. And the more the temperature approaches the Tg, the more gesture for the side groups. Since these gestures will do excess energy loss by molecular interaction, the loss modulus additions. After Tg, the free volume of the whole polymer additions and the section of the ironss begin to rotary motion and show snap [ 5 ] . So the interaction of the polymer ironss lessenings and the loss modulus lessenings. When the free volume is large plenty, the interaction and clash between ironss turn to be really little and the sample reaches rubberlike province. The loss modulus so attack to zero. Therefore, the loss modulus curve has a upper limit at the glass passage temperature.

Comparing of PS and HIPS belongingss through DMA consequence

By comparing the DMA consequence of PS and HIPS, it can be found that the loss modulus and Tan delta for HIPS is lower than that for PS. Figure 1 and 2 besides show that the glass passage temperature of HIPS is lower PS and the storage modulus for PS is besides higher than HIPS.

For HIPS, gum elastic atoms were added in to modify the mechanical belongingss. As the glass passage temperature of gum elastic atoms is below room temperature, it is at rubbery province and the mobility of gum elastic concatenation sections was good at proving temperature scope. So the entire modulus and Tg of HIPS was lower than pure PS. Furthermore, as to the full response of the section gesture to use stress frequence will go on at lower temperature for HIPS, the tried Tg for HIPS is lower than PS. The gum elastic atoms besides reduced the storage modulus as the storage modulus for them is lower than pure PS. So the blend of them exhibit lower storage modulus.

The lower loss modulus of HIPS is besides caused by the added gum elastic atoms. The loss modulus can be calculated by the undermentioned equation:

[ 3 ]

Where is the tensile loss modulus and is the strain dawdling behind the emphasis by an angle. From the equation it can be known that the loss modulus of the gum elastic atoms is little since strain dawdling for the stuff in rubbery province is really low. So the entire loss modulus of HIPS is lower than pure PS because of adding stuffs with lower loss modulus.

If the experiment temperature is changed into -100 to 25, another two extremum may be observed in the consequence of PS and HIPS, which are iˆ and passages. When temperature is really low, there are merely local gestures. As temperature addition, foremost at passage, bending and stretching will go on. After that, at iˆ passage, the side group will get down to travel. Both of these two processs will do alterations in modulus and extremum can be observed [ 2 ] . Furthermore for HIPS, one more extremum may be appeared in the consequence. This is because that the glass passage temperature of the gum elastic atoms in HIPS is between -100 to 25. Therefore, extremum for gum elastic ‘s glass passage will be observed.

Decision

From this experiment, it is known that DMA can be used to observe the glass passage temperature in mechanical manner. Around the Tg, loss modulus every bit good as showed a maximal value and storage modulus began to diminish. The temperature when loss modulus range upper limit are normally defined as glass passage temperature. The grounds for the loss modulus has maximum around Tg may be: 1 ) the ironss can rightly response with the proving frequence and give the biggest energy dissipation ; 2 ) as the E ” is the minus derivate of E ‘ , when E ‘ has the largest decreasing at Tg, E ” will make maximal 3 ) at Tg, sample has low free volume every bit good as good local gesture and interaction which cause maximal inter-chain energy loss during proving. In DMA testing, higher proving frequence will give higher trial glass passage temperature which is because that higher frequence needs higher concatenation energy in order to response and give biggest energy dissipation. This experiment showed that for HIPS, as the gum elastic atoms were added in, it had lower glass passage temperature every bit good as modulus ( Both storage modulus and Storage modulus ) comparing with pure PS. If the testing temperature scope changed into -100 to 25, passages might be observed in. Furthermore, for HIPS, the glass passage extremum of gum elastic atoms may besides be observed.