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Nanocomposites by Extruder Processing

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    1. Nanocomposites by Extruder Processing Combined industrial and academic study. Published work extruding nanocomposites not include study of processing variables. This Phase I study is focussed on changing the extruder type and screw designs. Combined industrial and academic study. Published work extruding nanocomposites not include study of processing variables. This Phase I study is focussed on changing the extruder type and screw designs.

    2. To the speakers knowledge, the first literature example of an organo-MMT nanocomposite was in 1950. Union Oil Company patented an organoclay polyolefin composition in 1963. The teachings of this patent describe many techniques that are important today in nanocomposites such as melt blending, master batching and intercalation in the presence of a common swelling solvent. Unitika filed a patent application in 1976 describing an in situ process to make a polyamide nanocomposite. Toyota researchers work in nanocomposites highlighted to academic and industrial researchers the potential of nanocomposites. AlliedSignal patented melt blending as a process to make a nanocomposite using MMT treated with primary and secondary onium ions. To the speakers knowledge, the first literature example of an organo-MMT nanocomposite was in 1950. Union Oil Company patented an organoclay polyolefin composition in 1963. The teachings of this patent describe many techniques that are important today in nanocomposites such as melt blending, master batching and intercalation in the presence of a common swelling solvent. Unitika filed a patent application in 1976 describing an in situ process to make a polyamide nanocomposite. Toyota researchers work in nanocomposites highlighted to academic and industrial researchers the potential of nanocomposites. AlliedSignal patented melt blending as a process to make a nanocomposite using MMT treated with primary and secondary onium ions.

    3. Melt Blending Literature Nanocomposites have been made by melt blending as literature references in this figure describe. No literature reference, to our knowledge, presents the results of melt blending processing studies. Nanocomposites have been made by melt blending as literature references in this figure describe. No literature reference, to our knowledge, presents the results of melt blending processing studies.

    4. A nanocomposite is a resin containing a nano sized dispersed phase. Nanocomposites in this study are based on the clay mineral montmorillonite (MMT). Smectite is the mineral group. The clay mineral MMT a species in the the smectite group. MMT has a platy morphology seen both in the Bentonite rock and refined MMT. The TEM of MMT shows a cluster of platelets, 1nm thick and 50 - 500nm laterally. A nanocomposite is a resin containing a nano sized dispersed phase. Nanocomposites in this study are based on the clay mineral montmorillonite (MMT). Smectite is the mineral group. The clay mineral MMT a species in the the smectite group. MMT has a platy morphology seen both in the Bentonite rock and refined MMT. The TEM of MMT shows a cluster of platelets, 1nm thick and 50 - 500nm laterally.

    5. Smectite Clay Chemistry This figure shows an edge on view of a single platelet of MMT. MMT is an inorganic polymer tied together by bridging oxygens. There are two outer SiO4 layers are bridged to the inner Al(Mg, Fe)O4(OH)4. Some of the Al+3 are substituted by Mg+2 or Fe+2 causing an net negative charge on the platelet. The electrical imbalance is corrected by the presence of counter cations, like Na+. At SCP, we use quaternary ammonium cations (quats), to ion exchange with Na+. This allows us to make the inorganic MMT platelet surface organic. By changing the R groups of the quat, R1R2R3R4N+, the MMT can be made more compatible with the resin. This figure shows an edge on view of a single platelet of MMT. MMT is an inorganic polymer tied together by bridging oxygens. There are two outer SiO4 layers are bridged to the inner Al(Mg, Fe)O4(OH)4. Some of the Al+3 are substituted by Mg+2 or Fe+2 causing an net negative charge on the platelet. The electrical imbalance is corrected by the presence of counter cations, like Na+. At SCP, we use quaternary ammonium cations (quats), to ion exchange with Na+. This allows us to make the inorganic MMT platelet surface organic. By changing the R groups of the quat, R1R2R3R4N+, the MMT can be made more compatible with the resin.

    6. Nanocomposite Language The dispersed phase MMT is mixed with the resin by melt blending or extruding. Four separate or combinations of mixtures can result: - Tactoid: polymer encapsulates stacks of MMT platelets. - Intercalate: polymer chains enter between MMT parallel platelets. - Disordered intercalate: the MMT platelets are not parallel. - Delaminated or Exfoliated: MMT platlets separated and dispersed in the resin. The dispersed phase MMT is mixed with the resin by melt blending or extruding. Four separate or combinations of mixtures can result: - Tactoid: polymer encapsulates stacks of MMT platelets. - Intercalate: polymer chains enter between MMT parallel platelets. - Disordered intercalate: the MMT platelets are not parallel. - Delaminated or Exfoliated: MMT platlets separated and dispersed in the resin.

    7. The Processing Challenge SCP provides Cloisite as a powder with a mean of about 8?m particle size. Extrusion is used to melt blend the powder with the resin. In each particle of powder there are more than 3000 platelets. The processing challenge is to disperse not only the powder particles but also the platelets. Dispersion to individual platelets is needed to take advantage of the high aspect ratio (>50) and high surface area (>750m2/gm) of MMT. SCP provides Cloisite as a powder with a mean of about 8?m particle size. Extrusion is used to melt blend the powder with the resin. In each particle of powder there are more than 3000 platelets. The processing challenge is to disperse not only the powder particles but also the platelets. Dispersion to individual platelets is needed to take advantage of the high aspect ratio (>50) and high surface area (>750m2/gm) of MMT.

    8. Dispersion Study Design Model system chosen from past nanocomposite extrusion experience. Cloisite 30B exfoliates in Nylon 6, chosen as a control. Cloisite 15A intercalates or partially exfoliates in Nylon 6. Extruders were nominal 30mm diameter. Extrusion variables of feed rate, screw speed and temperature profile were held constant. The residence time varied with extruder and screw design, but was measured. Dispersion was monitored for each change in condition. Model system chosen from past nanocomposite extrusion experience. Cloisite 30B exfoliates in Nylon 6, chosen as a control. Cloisite 15A intercalates or partially exfoliates in Nylon 6. Extruders were nominal 30mm diameter. Extrusion variables of feed rate, screw speed and temperature profile were held constant. The residence time varied with extruder and screw design, but was measured. Dispersion was monitored for each change in condition.

    9. Single and Co Rotating Screws The single screw had a high intensity mixer at the end. Screw designs for the types of twin screw extruders were changed to increase the shear intensity. The Co Rotating Low Shear design has one kneading block section. The Co Rotating Medium Shear design has three kneading block sections. The single screw had a high intensity mixer at the end. Screw designs for the types of twin screw extruders were changed to increase the shear intensity. The Co Rotating Low Shear design has one kneading block section. The Co Rotating Medium Shear design has three kneading block sections.

    10. Leistritz Counter Rotating Intermeshing The Counter Rotating Intermeshing Low Shear screw is an open flighted pump. The Counter Rotating Intermeshing Medium Shear screw is a close flighted pump. The Counter Rotating Intermeshing High Shear screw is close flighted with shearing and turbine (slit stowing) elements added. The Counter Rotating Intermeshing Low Shear screw is an open flighted pump. The Counter Rotating Intermeshing Medium Shear screw is a close flighted pump. The Counter Rotating Intermeshing High Shear screw is close flighted with shearing and turbine (slit stowing) elements added.

    11. Leistritz Counter Rotating Non-Intermeshing The Counter Rotating Non-Intermeshing (Tangential) Low Shear screw is a simple pump. The Counter Rotating Non-Intermeshing Medium Shear screw has one shearing and one reverse element added. The Counter Rotating Non-Intermeshing High Shear screw has four shearing and two turbine elements added (and the reverse element removed). The Counter Rotating Non-Intermeshing (Tangential) Low Shear screw is a simple pump. The Counter Rotating Non-Intermeshing Medium Shear screw has one shearing and one reverse element added. The Counter Rotating Non-Intermeshing High Shear screw has four shearing and two turbine elements added (and the reverse element removed).

    12. XRD Examples: 15A/PA6 Delamination dispersion is monitored by X-Ray Diffraction (XRD) and by Transmission Electron Microscopy (TEM). Four sample XRD are shown in the figure. MMT with its ordered platy morphology causes x-rays to diffract indicating the distance from the top of one platelet to the top of the next platelet (Basal Spacing or D001 Spacing). The organoclay Cloisite 15A has a d-spacing of about 32. When Cloisite15A is compounded with PA6 in a single screw extruder, the peak intensity decreases, the peak shape broadens but the peak position remains at about 32. Co Rotating Low Shear and Medium Shear samples further decrease in size and show the platelets mover further apart, 34 and 38, respectively. The sample made in the Tangential Medium Shear extruder showed no XRD peak. The lack of XRD peak suggests either an exfoliated or an intercalated disordered nanocomposite. TEM is required to see what the platelet distribution looks like. Delamination dispersion is monitored by X-Ray Diffraction (XRD) and by Transmission Electron Microscopy (TEM). Four sample XRD are shown in the figure. MMT with its ordered platy morphology causes x-rays to diffract indicating the distance from the top of one platelet to the top of the next platelet (Basal Spacing or D001 Spacing). The organoclay Cloisite 15A has a d-spacing of about 32. When Cloisite15A is compounded with PA6 in a single screw extruder, the peak intensity decreases, the peak shape broadens but the peak position remains at about 32. Co Rotating Low Shear and Medium Shear samples further decrease in size and show the platelets mover further apart, 34 and 38, respectively. The sample made in the Tangential Medium Shear extruder showed no XRD peak. The lack of XRD peak suggests either an exfoliated or an intercalated disordered nanocomposite. TEM is required to see what the platelet distribution looks like.

    13. TEM Examples: 15A/PA6 The TEM of the sample from the Single Screw extruder shows big ribbons that are of stacks of intercalated platelets. The samples from the Co Rotating extruder show increasing dispersion as the ribbons get smaller and some single platelets can be seen, particularly in the sample from the Medium Shear extruder. The sample from the Tangential Medium Shear extruder shows excellent delamination and dispersion. The TEM of the sample from the Single Screw extruder shows big ribbons that are of stacks of intercalated platelets. The samples from the Co Rotating extruder show increasing dispersion as the ribbons get smaller and some single platelets can be seen, particularly in the sample from the Medium Shear extruder. The sample from the Tangential Medium Shear extruder shows excellent delamination and dispersion.

    14. TEM Dispersion To compare the results of different TEM, a descriptive number needs to be assigned to each TEM. Twelve 1 squares were cut from a piece of paper. The paper was laid over a TEM and the number of platelets or intercalants in each square were counted and an average number of platelets/intercalants per square inch determined. This number is called the TEM Dispersion. The larger the TEM Dispersion, the better the delamination and dispersion. To compare the results of different TEM, a descriptive number needs to be assigned to each TEM. Twelve 1 squares were cut from a piece of paper. The paper was laid over a TEM and the number of platelets or intercalants in each square were counted and an average number of platelets/intercalants per square inch determined. This number is called the TEM Dispersion. The larger the TEM Dispersion, the better the delamination and dispersion.

    15. This figure shows the TEM Dispersion versus the process condition of changing the extruder type and screw configurations. The two clay treatments are compared in the Single Screw and Counter Rotating Intermeshing extruders. In both cases the TEM Dispersion is better for Cloisite 30B. Comparing Cloisite 30B and Cloisite 15A for the Single Screw extruder, one can see that a Single Screw extruder does not give sufficient delamination. All the extruder types are compared with Cloisite 15A and show differences in TEM Dispersion. Changing screw designs for any of the types of twin screw extruders leads to differences in TEM Dispersion. Implications SCP needs to continue developing treatments that are more compatible with various resins. Compounders need to change screw designs (twin screw extruder) and process conditions to optimize dispersion. This figure shows the TEM Dispersion versus the process condition of changing the extruder type and screw configurations. The two clay treatments are compared in the Single Screw and Counter Rotating Intermeshing extruders. In both cases the TEM Dispersion is better for Cloisite 30B. Comparing Cloisite 30B and Cloisite 15A for the Single Screw extruder, one can see that a Single Screw extruder does not give sufficient delamination. All the extruder types are compared with Cloisite 15A and show differences in TEM Dispersion. Changing screw designs for any of the types of twin screw extruders leads to differences in TEM Dispersion. Implications SCP needs to continue developing treatments that are more compatible with various resins. Compounders need to change screw designs (twin screw extruder) and process conditions to optimize dispersion.

    16. In this study the residence time was allowed to change with each extruder and screw design. Shown in the plot of TEM Dispersion versus Mean Residence Time for the Cloisite 15A nanocomposites is a general trend that increasing the residence time improves dispersion. In this study the residence time was allowed to change with each extruder and screw design. Shown in the plot of TEM Dispersion versus Mean Residence Time for the Cloisite 15A nanocomposites is a general trend that increasing the residence time improves dispersion.

    17. This figure shows a more detailed evaluation of TEM Dispersion and Mean Residence Time. For the Co Rotating extruder, only two screw configurations were run. Three configurations were run for both the Counter Rotating Intermeshing and Counter Rotating Non-Intermeshing extruders. In each configuration change from low shear to medium shear intensity, the Mean Residence Time increased and the TEM Dispersion increased. Increasing the shear intensity from medium shear to high shear caused a decrease in TEM Dispersion. For the Counter Rotating Intermeshing extruder the Mean Residence Time increased, but for the Counter Rotating Non-Intermeshing extruder the Mean Residence Time decreased. A conclusion from this information is that increasing the residence time is important, but the shear intensity of the screw is also important. From the TEM and XRD one can conclude the 8?m particles are sheared apart, presumably after intercalation, to form the big ribbons. Increasing shear intensity does not continue to shear the platelets apart that are in a small ribbon intercalant. This figure shows a more detailed evaluation of TEM Dispersion and Mean Residence Time. For the Co Rotating extruder, only two screw configurations were run. Three configurations were run for both the Counter Rotating Intermeshing and Counter Rotating Non-Intermeshing extruders. In each configuration change from low shear to medium shear intensity, the Mean Residence Time increased and the TEM Dispersion increased. Increasing the shear intensity from medium shear to high shear caused a decrease in TEM Dispersion. For the Counter Rotating Intermeshing extruder the Mean Residence Time increased, but for the Counter Rotating Non-Intermeshing extruder the Mean Residence Time decreased. A conclusion from this information is that increasing the residence time is important, but the shear intensity of the screw is also important. From the TEM and XRD one can conclude the 8?m particles are sheared apart, presumably after intercalation, to form the big ribbons. Increasing shear intensity does not continue to shear the platelets apart that are in a small ribbon intercalant.

    18. Dispersion Mechanism This figure proposes a mechanism for nanocomposite formation based upon a combination of chemical compatibility and processing. Not all comments are based on this study. Case 1, Compatible Clay Treatment and Resin Chemistry: - Most any processing condition (except a single screw extruder will yield delamination and dispersion. - The platelets almost explode to come apart. - Example is PA6 and Cloisite 30B. Case 3, Clay Treatment Not Compatible with Resin Chemistry: - Process changes can help reduce the size of the intercalant, but condition changes (to date) do not led to delamination and dispersion. - Example is PP and standard organoclays. Case 2, Partially Compatible Clay Treatment and Resin Chemistry: - Varying extruder conditions and screw design can improve delamination and dispersion. - Examples are PA6 and Cloisite 15A and PP and Cloisite 15A with maleated PP. This figure proposes a mechanism for nanocomposite formation based upon a combination of chemical compatibility and processing. Not all comments are based on this study. Case 1, Compatible Clay Treatment and Resin Chemistry: - Most any processing condition (except a single screw extruder will yield delamination and dispersion. - The platelets almost explode to come apart. - Example is PA6 and Cloisite 30B. Case 3, Clay Treatment Not Compatible with Resin Chemistry: - Process changes can help reduce the size of the intercalant, but condition changes (to date) do not led to delamination and dispersion. - Example is PP and standard organoclays. Case 2, Partially Compatible Clay Treatment and Resin Chemistry: - Varying extruder conditions and screw design can improve delamination and dispersion. - Examples are PA6 and Cloisite 15A and PP and Cloisite 15A with maleated PP.

    19. Dispersion Mechanism This figure continues the proposed mechanism. Particles of organoclay, with >3000 platelets, fracture to ribbons of intercalants or tactoids. It is proposed this is a results of shearing stacks of platelets apart to make shorter stacks of platelets. Ribbons reach a size where shearing no longer reduces the ribbon size (the number of platelets in a stack). Platelets in the ribbons delaminate by peeling apart. This happens after more polymer chains enter the clay galleries and push the platelets further apart. At either some polymer concentration or some platelet separation distance, the platelets peel away from the ribbon to be dispersed as individual platelets. This figure continues the proposed mechanism. Particles of organoclay, with >3000 platelets, fracture to ribbons of intercalants or tactoids. It is proposed this is a results of shearing stacks of platelets apart to make shorter stacks of platelets. Ribbons reach a size where shearing no longer reduces the ribbon size (the number of platelets in a stack). Platelets in the ribbons delaminate by peeling apart. This happens after more polymer chains enter the clay galleries and push the platelets further apart. At either some polymer concentration or some platelet separation distance, the platelets peel away from the ribbon to be dispersed as individual platelets.

    20. Dispersion: Particles Shear Apart Platelets Peel Apart A number of TEMs have been examined during this and other nanocomposite studies at SCP. The small picture in the figure shows the result of particles being sheared to ribbons, stacks of many platelets more than 100nm thick. The ribbons seen in this TEM are common for Case 3 Nanocomposites. TEM evidence of platelets peeling apart is not common, but has been seen multiple times with a representative TEM shown in the larger picture in the figure.. One of the regions where the platelets are peeling apart from the ribbon is outlined in the TEM. A number of TEMs have been examined during this and other nanocomposite studies at SCP. The small picture in the figure shows the result of particles being sheared to ribbons, stacks of many platelets more than 100nm thick. The ribbons seen in this TEM are common for Case 3 Nanocomposites. TEM evidence of platelets peeling apart is not common, but has been seen multiple times with a representative TEM shown in the larger picture in the figure.. One of the regions where the platelets are peeling apart from the ribbon is outlined in the TEM.

    21. The focus of this study was delamination and dispersion. A few mechanical properties were also measured. This figure shows the tensile modulus increases as TEM Dispersion increases. A big increase in tensile modulus occurs by reinforcing the PA6 with ribbons of clay tactoids or intercalants. The focus of this study was delamination and dispersion. A few mechanical properties were also measured. This figure shows the tensile modulus increases as TEM Dispersion increases. A big increase in tensile modulus occurs by reinforcing the PA6 with ribbons of clay tactoids or intercalants.

    22. Conclusions To make a nanocomposite with good delaminated dispersion, both the clay treatment chemistry and the extruder screw design (and process conditions) need to be optimized. Increasing residence time in general improves delaminated dispersion, but there is an optimum of shear intensity that can be applied after which delaminated dispersion gets worse. In designing a screw configuration, take into account the proposed dispersion mechanism. Shear is required to start the dispersion process. This shear promotes the intercalate ribbons to reduced in size. Residence time in a non-shearing extruder environment is then needed to allow the platelets to peel apart. These are ideas based upon the process studies to date, more work is needed to improve our understanding of screw design and then begin making the more traditional variable changes such as feed rate, screw speed, temperature profile and feed points for resin and clay. To make a nanocomposite with good delaminated dispersion, both the clay treatment chemistry and the extruder screw design (and process conditions) need to be optimized. Increasing residence time in general improves delaminated dispersion, but there is an optimum of shear intensity that can be applied after which delaminated dispersion gets worse. In designing a screw configuration, take into account the proposed dispersion mechanism. Shear is required to start the dispersion process. This shear promotes the intercalate ribbons to reduced in size. Residence time in a non-shearing extruder environment is then needed to allow the platelets to peel apart. These are ideas based upon the process studies to date, more work is needed to improve our understanding of screw design and then begin making the more traditional variable changes such as feed rate, screw speed, temperature profile and feed points for resin and clay.