Chemical structure of PEI 

Contexts in source publication

Context 1

... exposed samples were subjected to aggressive chemical environments and it is observed that there is a significant loss in the tensile strength of polymeric samples when subjected to alkaline environments. The tensile strength of exposed samples under aggressive chemical environment is as shown in Figure 12. Rabilloud (1999) observed that polyimides exhibit relatively good hydrolytic stability in neutral or acidic aqueous environments. They also observed that most of the polyimides undergo hydrolytic degradation in the presence of alkaline aqueous solutions. Hydrolytic degradation occurs in polymers that have water-sensitive active groups, especially those that take a lot of moisture. Figure 12 clearly indicates that there is a significant decrease in the tensile strength of exposed PEI under the influence of basic medium. There is also a decline in the tensile strength of PEI composites exposed to basic environments. This is because of the hydrolytic degradation of polymers. Hydrolytic attack on the imide ring reverses the polymerisation reaction resulting in the formation of the polyamic acid, followed by chain scission and associated molecular weight and strength decreases resulting ultimately in regeneration of the monomers (Rabilloud, 1999). The reinforcement of CNF compensates for the loss in mechanical properties of PEI. Chemical exposure ordinarily results in a softening effect, or cracking and crazing of the thermoplastic. As softening of the PEI occurs, the per cent weight increases while tensile strength decreases. It can be noted that there is a 60% decrease in the tensile strength of PEI from 100 MPa to 40 MPa when exposed under basic environment. The presence of nano particles nullifies the effect of basic environment on PEI composites to 42%. The tensile strength of the PEI composites reduces from 135 MPa to 78 MPa. Researches have in the past given significant evidence for the reduced permeability due to the presence of nano materials in polymers ( Khan et al., 2013). Nawani et al. (2015) found that the addition of nano carbon black and nano organoclays greatly enhances the tortuosity by the joining of carbon black and organoclays leading to reduced permeability and enhanced barrier properties of the polymers to chemicals and other ...

Context 2

... exposed samples were subjected to aggressive chemical environments and it is observed that there is a significant loss in the tensile strength of polymeric samples when subjected to alkaline environments. The tensile strength of exposed samples under aggressive chemical environment is as shown in Figure 12. Rabilloud (1999) observed that polyimides exhibit relatively good hydrolytic stability in neutral or acidic aqueous environments. They also observed that most of the polyimides undergo hydrolytic degradation in the presence of alkaline aqueous solutions. Hydrolytic degradation occurs in polymers that have water-sensitive active groups, especially those that take a lot of moisture. Figure 12 clearly indicates that there is a significant decrease in the tensile strength of exposed PEI under the influence of basic medium. There is also a decline in the tensile strength of PEI composites exposed to basic environments. This is because of the hydrolytic degradation of polymers. Hydrolytic attack on the imide ring reverses the polymerisation reaction resulting in the formation of the polyamic acid, followed by chain scission and associated molecular weight and strength decreases resulting ultimately in regeneration of the monomers (Rabilloud, 1999). The reinforcement of CNF compensates for the loss in mechanical properties of PEI. Chemical exposure ordinarily results in a softening effect, or cracking and crazing of the thermoplastic. As softening of the PEI occurs, the per cent weight increases while tensile strength decreases. It can be noted that there is a 60% decrease in the tensile strength of PEI from 100 MPa to 40 MPa when exposed under basic environment. The presence of nano particles nullifies the effect of basic environment on PEI composites to 42%. The tensile strength of the PEI composites reduces from 135 MPa to 78 MPa. Researches have in the past given significant evidence for the reduced permeability due to the presence of nano materials in polymers ( Khan et al., 2013). Nawani et al. (2015) found that the addition of nano carbon black and nano organoclays greatly enhances the tortuosity by the joining of carbon black and organoclays leading to reduced permeability and enhanced barrier properties of the polymers to chemicals and other ...

Context 3

... order to find the mechanical properties of the polymeric nano composites, the exposed samples were subjected to mechanical testing. Tensile tests are also used to correlate the presence of chain scission or chain linking due to the exposure under radiation, thermal and chemical environments. The tensile strength and the elongation at break for the exposed samples are shown in Figures 10 and 11, respectively. Figure 10 clearly indicates that there is a marginal loss in tensile strength under the influence of radiation and thermal environments. Mittal (2013) observed that PEI retains their mechanical properties when exposed to 500 megarads of gamma radiation. A loss of merely 6% tensile strength was observed after cumulative exposure to 500 megarads at the rate of one megarad per hour using cobalt 60. Long and Long (1985) observed that there is a marginal decrease in the tensile strength when exposed to high doses of radiation. This is because imide ring opens at higher doses hence, forming cross-linking by the dangling side of carbonyl structure to form ladder cross-linking. Hence, the net effect of the ladder cross-linking would result in the small change in the tensile strength. It is also observed that there is an increase in the tensile strength of PEI composites due to the influence of CNF. CNF when reinforced in PEI gives increased strength due to the exceptional strength of the nano filler combined with the large surface area ( Liu and Kumar, 2014;Kumar, 2007). Figure 11 clearly indicates that there is a marginal change in the elongation of the polymeric nano composites before and after exposure to radiation and thermal environments. The elongation of composites gives a clear insight on the degree of mechanical deterioration of the polymers before and after exposure. This finding may also be attributed to the absence of high degree of chain scission in the polymers due to radiation and thermal ...

Context 4

... order to find the mechanical properties of the polymeric nano composites, the exposed samples were subjected to mechanical testing. Tensile tests are also used to correlate the presence of chain scission or chain linking due to the exposure under radiation, thermal and chemical environments. The tensile strength and the elongation at break for the exposed samples are shown in Figures 10 and 11, respectively. Figure 10 clearly indicates that there is a marginal loss in tensile strength under the influence of radiation and thermal environments. Mittal (2013) observed that PEI retains their mechanical properties when exposed to 500 megarads of gamma radiation. A loss of merely 6% tensile strength was observed after cumulative exposure to 500 megarads at the rate of one megarad per hour using cobalt 60. Long and Long (1985) observed that there is a marginal decrease in the tensile strength when exposed to high doses of radiation. This is because imide ring opens at higher doses hence, forming cross-linking by the dangling side of carbonyl structure to form ladder cross-linking. Hence, the net effect of the ladder cross-linking would result in the small change in the tensile strength. It is also observed that there is an increase in the tensile strength of PEI composites due to the influence of CNF. CNF when reinforced in PEI gives increased strength due to the exceptional strength of the nano filler combined with the large surface area ( Liu and Kumar, 2014;Kumar, 2007). Figure 11 clearly indicates that there is a marginal change in the elongation of the polymeric nano composites before and after exposure to radiation and thermal environments. The elongation of composites gives a clear insight on the degree of mechanical deterioration of the polymers before and after exposure. This finding may also be attributed to the absence of high degree of chain scission in the polymers due to radiation and thermal ...

Context 5

... order to find the mechanical properties of the polymeric nano composites, the exposed samples were subjected to mechanical testing. Tensile tests are also used to correlate the presence of chain scission or chain linking due to the exposure under radiation, thermal and chemical environments. The tensile strength and the elongation at break for the exposed samples are shown in Figures 10 and 11, respectively. Figure 10 clearly indicates that there is a marginal loss in tensile strength under the influence of radiation and thermal environments. Mittal (2013) observed that PEI retains their mechanical properties when exposed to 500 megarads of gamma radiation. A loss of merely 6% tensile strength was observed after cumulative exposure to 500 megarads at the rate of one megarad per hour using cobalt 60. Long and Long (1985) observed that there is a marginal decrease in the tensile strength when exposed to high doses of radiation. This is because imide ring opens at higher doses hence, forming cross-linking by the dangling side of carbonyl structure to form ladder cross-linking. Hence, the net effect of the ladder cross-linking would result in the small change in the tensile strength. It is also observed that there is an increase in the tensile strength of PEI composites due to the influence of CNF. CNF when reinforced in PEI gives increased strength due to the exceptional strength of the nano filler combined with the large surface area ( Liu and Kumar, 2014;Kumar, 2007). Figure 11 clearly indicates that there is a marginal change in the elongation of the polymeric nano composites before and after exposure to radiation and thermal environments. The elongation of composites gives a clear insight on the degree of mechanical deterioration of the polymers before and after exposure. This finding may also be attributed to the absence of high degree of chain scission in the polymers due to radiation and thermal ...

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... is the only technique available to characterise the molecular weight distribution of polymers. GPC is performed to understand the effect of chemical environment on the molecular weight of polymeric samples. The molecular weight of samples measured from GPC is shown in Figure 13. Figure 13 gives clear indication that there is a significant reduction in the molecular weight of polymer when exposed to radiation, thermal and basic environment. It can be concluded that there are no significant changes in the molecular weight of polymer when exposed to radiation, thermal and acidic environment. Therefore, it is clearly evident from the figure that the influence of basic medium on the polymer reduces the molecular weight of polymer. Polymer degradation generally involves changes to the molecular weight of the polymer and typical property changes include reduced ductility and embrittlement, chalking, colour changes, cracking, general reduction in most other desirable physical properties ( Villetti et al., 2002). Hydrolytic attack on the imide ring reverses the polymerisation reaction resulting in the formation of the polyamic acid. This polyamic acid results in chain scission of the polymeric chain and further reduces the molecular weight of the ...

Context 7

... is the only technique available to characterise the molecular weight distribution of polymers. GPC is performed to understand the effect of chemical environment on the molecular weight of polymeric samples. The molecular weight of samples measured from GPC is shown in Figure 13. Figure 13 gives clear indication that there is a significant reduction in the molecular weight of polymer when exposed to radiation, thermal and basic environment. It can be concluded that there are no significant changes in the molecular weight of polymer when exposed to radiation, thermal and acidic environment. Therefore, it is clearly evident from the figure that the influence of basic medium on the polymer reduces the molecular weight of polymer. Polymer degradation generally involves changes to the molecular weight of the polymer and typical property changes include reduced ductility and embrittlement, chalking, colour changes, cracking, general reduction in most other desirable physical properties ( Villetti et al., 2002). Hydrolytic attack on the imide ring reverses the polymerisation reaction resulting in the formation of the polyamic acid. This polyamic acid results in chain scission of the polymeric chain and further reduces the molecular weight of the ...

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... is an amorphous, amber-to-transparent thermoplastic with characteristics consisting of high mechanical properties and exceptional thermal resistance. Its chemical and mechanical properties are outstanding and well comparable to those of metals and alloys for the mechanical properties. In some cases, the chemical properties of PEI are much superior to metals. While metals and metallic alloys undergo corrosion-type chemical degradation, by their nature, polymers do not experience corrosion. However, other types of chemical aggression may lead to the degradation of the material, but PEI has been proven to have a very high resistance to these chemical reactions. Similar to other radiation resistant polymers, the presence of aromatic groups increases the delocalised pi electron ( Bonin et al., 2001). Its chemical and mechanical properties are outstanding when compared to those of metals and alloys. The chemical structure of PEI is shown in Figure 1. The lower processing temperature and higher thermal stability make PEI a potential candidate for nuclear radiation shielding. The extent of interaction between the reinforcement and the matrix varies from strong chemical bonding to weak frictional forces. This can often be controlled by using an appropriately modifying the reinforcing ...

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... chemical and mechanical properties are outstanding when compared to those of metals and alloys. The chemical structure of PEI is shown in Figure 1. The lower processing temperature and higher thermal stability make PEI a potential candidate for nuclear radiation shielding. ...

Context 10

... tests are also used to correlate the presence of chain scission or chain linking due to the exposure under radiation, thermal and chemical environments. The tensile strength and the elongation at break for the exposed samples are shown in Figures 10 and 11, respectively. Figure 10 clearly indicates that there is a marginal loss in tensile strength under the influence of radiation and thermal environments. ...

Context 11

... tensile strength and the elongation at break for the exposed samples are shown in Figures 10 and 11, respectively. Figure 10 clearly indicates that there is a marginal loss in tensile strength under the influence of radiation and thermal environments. Mittal (2013) observed that PEI retains their mechanical properties when exposed to 500 megarads of gamma radiation. ...

Context 12

... when reinforced in PEI gives increased strength due to the exceptional strength of the nano filler combined with the large surface area ( Liu and Kumar, 2014;Kumar, 2007). Figure 11 clearly indicates that there is a marginal change in the elongation of the polymeric nano composites before and after exposure to radiation and thermal environments. The elongation of composites gives a clear insight on the degree of mechanical deterioration of the polymers before and after exposure. ...

Context 13

... exposed samples were subjected to aggressive chemical environments and it is observed that there is a significant loss in the tensile strength of polymeric samples when subjected to alkaline environments. The tensile strength of exposed samples under aggressive chemical environment is as shown in Figure 12. Rabilloud (1999) observed that polyimides exhibit relatively good hydrolytic stability in neutral or acidic aqueous environments. ...

Context 14

... degradation occurs in polymers that have water-sensitive active groups, especially those that take a lot of moisture. Figure 12 clearly indicates that there is a significant decrease in the tensile strength of exposed PEI under the influence of basic medium. There is also a decline in the tensile strength of PEI composites exposed to basic environments. ...

Context 15

... is performed to understand the effect of chemical environment on the molecular weight of polymeric samples. The molecular weight of samples measured from GPC is shown in Figure 13. Figure 13 gives clear indication that there is a significant reduction in the molecular weight of polymer when exposed to radiation, thermal and basic environment. ...

Context 16

... molecular weight of samples measured from GPC is shown in Figure 13. Figure 13 gives clear indication that there is a significant reduction in the molecular weight of polymer when exposed to radiation, thermal and basic environment. It can be concluded that there are no significant changes in the molecular weight of polymer when exposed to radiation, thermal and acidic environment. ...