ABS-PC
> Chemical composition and synthesis
ABS-PC is a blend of two thermoplastics, polyacrylonitrile–polybutadiene–polystyrene terpolymer (ABS) and polycarbonate (PC), which ratio can vary according to the desired properties. Figure 1 shows the structure of both polymer chains. A more detailed description of ABS polymer is given in other section of this site (link ABS). The blend is commercially created by intimately mixing the two polymers during an extrusion process. [2]
Figure 1: Chemical structures of both PC and ABS polymer chains. ABS is a terpolymer constituted of a polybutadiene backbone and sidearms of polyacrylonitrile and polystyrene.
> Properties
The advantage of this material is to combine properties of both PC and ABS. Indeed, ABS is an easy to process material, especially during extrusion, with great weathering and light stability while PC has overall good mechanical properties and temperature resistance [1, 2, 5].
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Published DSC results [4] let us consider the blend to be a triple phase mixture of butadiene rubber, PC and a styrene-acrylonitrile. According to the literature [2, 4], adhesion between ABS and PC is due to partial miscibility of PC and styrene-acrylonitrile phases, with a maximum when the acrylonitrile of this last phase is around 25-27% by weight. Considering the rheology, literature also proves that the mixture of PC, which has a high melt viscosity, and ABS creates a lower melt viscosities at 250°C than the one of pure PC and ABS [3]. To summarize the remaining properties, ABS-PC blends degrade when used in hot aqueous solution (above 50°C) for a long time. These are also swollen and partially dissolved if put in contact with ketones, aromatics, esters and hydrocarbons. In addition ABS-PC has good electrical insulation properties. [2]
> As printing material
According to the manufacturer, ABS-PC filaments should be printed with an extrusion temperature of 270-290°C with an heated beth at 110 to 140°C. It is very hydroscopic and should be dried for one hour in an oven to 90° and stored in a sealed container with desiccants. To avoid distortion and to ensure good layer adhesion of larger prints, it is recommended to print with a printer which has a closed printing area to keep a warm environment[6].
From personal experience, small prints can be printed in ABS-PC when printed in a enclosed printer with an extrusion temperature of 255°C and an heated bed at 130°C (maximum temperature reachable with a Makerbot Replicator© 2X). Figure 2 represents a dogbone-test print where strong warping is visible. However, other tests with larger samples resulted in failures due to loss of adhesion between the sample and the heated bed and even with various print conditions.
Figure 2: FDM print in ABS-PC of a so-called dogbone for mechanical tests.
> Bibliography
1. Balart, R., López, J., García, D. & Dolores Salvador, M. Recycling of ABS and PC from electrical and electronic waste. Effect of miscibility and previous degradation on final performance of industrial blends. European Polymer Journal 41, 2150–2160 (2005).
2. Huang, J.-C. & Wang, M.-S. Recent advances in ABS/PC blends. Advances in Polymer Technology 9, 293–299 (1989).
3. W. K. Chin and J. L. Hwung, SPE ANTEC, 33, 1379 (1987)
4. J. D. Keitz, J. W. Barlow. and D. R. Paul, J. Appl. Polym. Sci., 29, 3131
5. Liu, X. & Bertilsson, H. Recycling of ABS and ABS/PC Blends. Journal of Applied Polymer Science 74, 510–515 (1999).
6. High Temperature Polycarbonate-ABS Alloy. ProtoPlant, makers of Proto-pasta Available at: https://www.proto-pasta.com/products/pc-abs-alloy. (Accessed: 26th March 2017)
7. Hiemenz, P. C. & Lodge, T. Polymer chemistry. (CRC Press, 2007).
8. http://autonomyspaw.myfreesites.net/dsc (04/04/2017)
9. Chiang, W.-Y. & Hwung, D.-S. Properties of polycarbonate/acrylonitrile-butadiene-styrene blends. Polym Eng Sci 27, 632–639 (1987).
> Applications
> Experimental part
Rotational rheometry was performed on a ABS-PC sample at 250°C, which is the upper limit of the rheometer at our disposal. This temperature is well above the glass transition temperature of PC, but quite lower than the recommended extrusion temperature used in Fused Deposition Modelling (FDM) [6]. Therefore it can be supposed that the sample will be in a rubbery state and not liquid.
Measurements of the storage modulus G’, the loss modulus G” and the viscosity according to the shearing frequency are presented in Figure 4. G’ represents the elastic response of the material whereas G” represents the viscous response. Principally, the material behaves like a solid when G’>>G” and like a liquid when G”>>G’ [7]. This can be applied to polymers for very high frequency (glassy zone) and very low frequency (terminal zone) respectively, as shown in Figure 5. However, when we are working with polymers chains there is a third zone called the rubbery plateau in which the material is elastic. Entanglements between polymer chains is responsible for this behaviour [7]. In Figure 5 we can see that G” has two maxima, one stressing the transition of the glassy zone to the rubbery plateau and the other for the transition to the terminal zone. The former transition is due the constrained motion of monomers in between entanglements, whereas the latter transition is caused by the the movement of whole polymer chains.
As we consider our results from Figure 4, we can estimate that the ABS-PC sample at 250°C is in the middle of the rubbery zone. Indeed, G” is greater than G’ for higher frequencies till 0.32 Hz where G’ reaches a plateau and becomes greater than G” for lower frequencies, like the marked area in Figure 5. An interpretation for this transition could be related to entanglements being more dominant than the constrained motion of monomers. Moreover, the increase of viscosity with decreasing frequency is in agreement with this hypothesis.
Mainly, those interpretations show that ABS-PC at 250°C behaves more like a rubbery material than like a liquid, meaning that that at this temperature it is not ideal for prints made with FDM. In point of facts, the results after some prints was that the printed ABS-PC was rough, strong warping was occurring and there was loss of adhesion between some layers leading to failures. An attempt of print made out of ABS-PC is shown in Figure 2.
ABS-PC blends are widely used for making computers, equipment housing and in the automotive industry for the plastic parts of cars [1, 5].
>> Rheology
Figure 4: Dynamic moduli and viscosity dependent of the frequency from rotational rheology measurements for ABS-PC filament at 250°C.
Figure 5: Frequency dependency of storage modulus G’ and loss modulus G” for monodispersed polymer melt (a). From [8].
Differential Scanning Calorimetry is performed in order to estimate the glass transition temperature (Tg) of ABS-PC and to investigate if other processes are occurring. The results are presented in figure 6 in the form of a temperature dependent heat flow curve. As reference a DSC measurement of ABS-PC previously realised by an other group is presented in figure 7. We can note that the overall shape of the curve is the same as the reference, but with a different slope which may be related to a different apparatus and a different procedure when measuring. Three clear glass transition are visible. The first occurs from 108°C to 114°C, the second from 138°C to 147°C and the last one from 210°C to 220°C.The last one can not be identified and could be related to degradation of polybutadiene which is unstable at high temperature. The middle point of the first two transitions, which are 111°C and 142.5°C, give the Tg of the polyacrylonitrile-polystyrene (PA-PS) phase and the PC phase respectively. Comparing those results which the ones of figure 7 confirms this statement with Tg of 111.5°C and 144°C [8]. The small differences in value can be related to the different apparatus and difference in measuring conditions. According to the literature [9], the Tgs of ABS-PC vary with according to the ABS to PC ratio. Pure PC has a Tg of 145°C and the PA-PS phase of ABS has an average Tg of 95°C. However, the partial miscibility between PC and PA-PS lowers the Tg of PC phase while increasing this of PA-PS phase [9]. This correspond to our results. To conclude, our ABS-PC prints are solid at 120°C due to the high Tg of the PC phase but will be softer as a consequence of the lower Tg of PA-PS phase.
>> DSC
Figure 6: Graphic representation of experimental DSC results of ABS-PC sample.
Figure 7: DSC measurements of ABS-PC 3D printing filament, the red curve being the first cycle and the blue one the second cycle. From [8].
By Arthur
ABS-PC is a very interesting material because it combines the processability of ABS with the mechanical properties of PC. The DSC and the rheological measurements show that ABS-PC is difficult to melt at 250°C, which is unfortunately the maximum extrusion temperature of the printer. Tests done one more complicated samples than on dogbones resulted systematically in failures