ColorFabb_HT

What is colorfabb_HT ?

Amphora HT5300 3D is a polymer used to make ColorFabb_HT, a low-odor and styrene- and BPA-free material suited for advanced 3D printing users. The exact chemical composition of this polymer is proprietary of Eastman and is not provided.

Based on web searches, Amphora HT5300 was found to have similar characteristics as polycarbonate (PC) with respect to processing temperature and mechanical strength, but with lower fumes and better printability according to the supplier. Therefore, we describe PC because of the similar physical properties below although PC and Amphora HT5300 have quite different compositions ("chemical properties").

Physico-chemical properties

Polycarbonate is a high performance heterochain polymeric material part of the family of "engineering thermoplastics". PC is widely used in engineering for its featured temperature resistance, impact resistance and optical properties.

The main physico-chemical properties of PC are [1] :

High glass transition temperature (Tg) = 145°C due to a minimal molecular rotation about the bonds (linking the functional groups)
Moderate flexibility (though not as high as Nylon)
Good mechanical stability between -40°C and 140°C
High strength providing good resistance against impact and fracture
High electrical and heat resistance
Good transparency due to its amorphous structure attributed to PC's inability to crystallise by the presence of bisphenol A
Ease to reuse
Environmentally friendly process
Biological inertia

Synthesis route

As previously mentioned, PC presents quite similar physical properties HT53000 Polymer. However the chemical composition and synthesis routes of these two polymers do not match since colorFabb_HT is a BPA-free synthesized copolyester while bisphenol A is one of the main monomers polycarbonate is made of.

The main synthesis route is the step-growth polymerization (= condensation process) of Bisphenol A and Phosgene (COCl2) in which Cl ions are eliminated every time monomers react. The overall reaction scheme is shown in figure 1 although it should be mentioned that this condensation process is not straightforward. Indeed, this process consists of three steps which are not discussed here but can be found here [1].

Figure 1 : Net reaction of polycarbonate synthesis via phosgenation

The physico-chemical properties of our polymer of interest, the HT5300 Polymer, are listed in table 1 [2] :

Table 1 : Physico-chemical properties of ColorFabb HT5300 Polymer [3], [4]

The colorfabb Family

This polymer is part of the ColorFabb family co-polyesters, which includes 3 types of co-polyesters, each with different material characteristics : ColorFabb nGen, ColorFabb_XT and ColorFabb_HT.
These materials share common characteristics as good chemical resistance, styrene-free and BPA-free printing and FDA food contact compliance.

ColorFabb_HT is made for advanced professional users who have very specific needs in terms of temperature resistance and material toughness.

Performance and printing characteristics of several Amphora 3D polymers can be matched and compared with ABS and PLA in the following figure : [3]

Figure 2 : Performance and printing characteristics of Amphora polymers

Application field

1. Automotive.
ColorFabb_HT combines high toughness, temperature resistance and durable mechanical properties, which is particularly suited for applications in industries such as automotive : parts of the engine bay, functional brackets, clamps, etc.

2. Functional prototyping
ColorFabb_HT also suits for headphone or housing for holding electronic parts which need to have a material with good stability and high temperature resistance.

3. Durable parts
ColorFabb_HT is used to customize tools and clamps, because of its durable nature.

The printing material

According to Eastman, the Amphora 5300XT is a low-odor, styrene and BPA free material suited for 3D printing. This polymer is advantageous because of its wide temperature printing range thanks to its good flow properties.

As previously mentioned, ColorFabb_HT shows enhanced toughness and temperature resistance properties compared to its nGen competitor, which already exhibited remarkable printing properties. This polymer has been more deeply described by a co-worker on another website page.

Processing properties

ColorFabb [4] and Eastman [5] give some recommendations for the printing parameters :

Heated bed temperature = 60°C
Printing temperature between 250 and 280°C.
A printing speed range from 30 to 60 mm/s (even up to 100 mm/s according to Eastman's guide [2] )
Fluent printing conditions (avoid cooling) to get best possible strength, better layer adhesion and less issues with warping of the material

It’s important to note that the processing temperature is higher than the Tg, allowing the polymer to flow properly. On the contrary, the temperature of the bed is lower than Tg in order to allow the polymer to get solid when put in contact with this bed. If on the contrary the temperature was higher than the Tg, the polymer would remain viscous and wouldn’t bind properly with the bed.

It should be mentioned that these ranges for the processing parameters vary from one source to another and even in the same source. Indeed, the range of values given in the Eastman's datasheets available on their website are not consistent with the manufacturer's directives provided with the product package.

For example, Eastman suggests in their datasheet to print on a heated build plate around 60°C whereas ColorFabb recommends on their website 110-120°C for the heated bed temperature to avoid warping, which is twice as much. In this case, this difference could be explained by the fact that the second range is specific to glassplate heated build plates.

In our case, we don't have a glassplate as build plate, hence the parameters of the technical sheet available on the manufacturer's website have been chosen as a starting point for our 3D-printing campaign. Starting with the lowest temperature range for heating the bed seemed less "risky" and this temperature can be further progressively increased if needed.

Experimental analysis

3D-Printing test

As previously mentioned, the printing guidelines of the manufacturer's datasheet have been used as starting point in order to print one of the two "test model objects" among which the dogbone has arbitrarily been chosen.

For the first trial, the main parameters used were:

20% fill
Heated bed temperature = 80 °C
Printing speed = 60 mm/s
Printing T° = 255°C

This first trial failed since after the raft/support was printed, the printing head was operating in void-mode, meaning that the head was moving without any polymer being extruded from it. This coud be due to the fact that during the raft printing procedure, the software was stopped for a few seconds to have a better look at the printed raft part so far. However, even though this lasted only a few seconds, the polymer seemed to solidify in some way and hence clog the head. Furthermore, some printing defaults and inaccuracies were observed which could suggest a too high printing speed. Besides, warping was also observed which suggested a too cold printing bed. Hence an increase of the heated bed temperature seemed necessary.

For the second test, some parameters have been adjusted consistent with the observations after the first trial:

Heated bed T° = 90°C
Printing Speed = 40 mm/s
Printing temperature = 256°C (=maximal capacity of the printer)

The second printing trial succeeded and the result can be seen on the following figures (2) and (3).

Figure 3 : Dogbone in colorFabb_HT for printing test

Figure 4 : Dogbone's raft after printing test

DSC

At the beginning of this experiment, a first heating of the polymer was performed in order to "erase its memory". Then, the polymer was cooled down to room temperature at a specific cooling rate. Afterwards, the polymer was finally heated a second time to provide (the) valuable information.

The analytical conditions must be thoroughly taken care of as they have a direct impact on the obtained results (e.g. if the cooling rate decreases, the measured Tg decreases too). So, the quality of our results depends on the latter.

In our case, the operating conditions were the following :

Identical heating and cooling rates : 10 °C /min
mass of polymer used ~ 7.5 mg (coming from the untreated polymer coil)

Figure 5 : DSC of colorFabb_HT with the three operating regimes : Heat - Cool - Reheat

As shown in the above figure, the black and green curves correspond to the first and second heating respectively. This progressive heating procedure is performed from room temperature up to 265°C, while the blue curve matches the reverse cooling process.

By the means of the above given datasheet, one can know that according to the manufacturer, the Tg of our material equals 100°C and the decomposition temperature of the materials exceeds 300°C.

Firstly, one can clearly see on the graph a glass transition around 100°C for the two heating curves, characterized by the first jump. According to literature, this peak corresponds to an endothermic peak of relaxation of the polymer material.

Secondly, the black curve shows a second peak, exothermic this time, around 250°C which might match the crystallisation upon heating of the material. This behaviour is not observed on the green curve which could be explained by the thermal history of the polymer. This also could be due to some degradation of it.

Normally, since the melting temperature (Tm) of the polymer exceeds 300°C, one would expect a second endothermic melting peak at higher temperatures. Since we didn't go at such high temperatures with our experiment, we cannot make any conclusions about it. If it was observed, this pre-melting transition would have matched with the transition from the semi-crystalline phase towards the amorphous one of our thermoplastic polymer.

Finally, the blue cooling curve on the other hand shows a transition around 100°C and further, a small peak around 35-40 °C.

Rheometry

The rheology of materials allows to obtain the mechanical properties of materials showing a viscoelastic behavior, hence this analysis is suitable for melt polymers.

When applying a dynamic strain/stress to the polymer, it can provide two responses: an elastic response (G') and a viscous response (G"). The latter correspond respectively to the in and out of phase responses with respect to the applied strain/stress.

Knowing this, the dynamic modulus can then be written as :

Through this experimental part, several types of sweeping tests were performed. First, the sweep-strain test was carried out at 220°C as a starting test for our material by operating at constant constant angular frequency and applying a variable strain (see Page about Rheometry) in order to analyse the linear domain of the material. A linear regime has been observed up to 20% strain (results not shown on this page).

It should be mentioned that this sample was very tricky to prepare for rheometry analysis. Indeed, lots of issues were encountered upon loading of this material, which showed a "bad warping behaviour" around 200°C.

The second part and final goal of this experiment was to perform a frequency sweep. The latter consists of applying a fixed strain (5% in our case) while varying the angular frequency of the oscillating plate, which allows a homogeneous deformation of the sample.

Several measurements were made each with a strain of 5%. Chronologically, pair frequency sweep tests at 200, 220, 230, 240 and 250°C were performed.

Finally, two thermal sweep tests were made operating between 190 °C and 250°C.

These "pair" typical repetition patterns in rheometry are there to show the reproducibility of the measurements.

5

Figure 6 : Rheological characterisation curves of the storage modulus G' and loss modulus G"

The obtained results are almost the same as the one observed for the nGen colorFabb which have been clearly outlined HERE in the Rheometry part.

Therefore, in order to avoid the repetition of what has already been explicitly presented for that material, I refer you to it and only the last thermal sweep test will be presented here along with the complex viscosity of the material.

When increasing our operating temperature, the polymer viscosity decreases as can be seen on the above picture. This can be related to the thermal activation of modes of chain motion within the polymer. It is also possible, assuming the material owns a crystalline portion, that this viscosity decrease is due to the melting of the crystals.

Regarding the behaviour at constant temperature, we can see that for high temperature (e.g. 250°C), the viscosity seems to remain constant over the whole frequency range. The latter implies that the 3D printing parameters (such as printing speed, extrusion speed, ...) have almost no influence on the viscous response of the polymer whereas for the lower temperature, the material is more sensitive to these parameters.

As previously introduced, the damping factor corresponds to the direct ratio of the viscous and elastic parts of the modulus = G"/G'.

If this ratio G"/G' > 1, the polymer can be featured as a damping material which means that it tends to decrease perceived vibrations and dissipate the energy resulting from an impact into heat.

In our case, the colorFabb_HT only shows a damping behaviour at 250°C. Below this temperature the material features a damping factor ranging between 0,1 and 1 and hence corresponding to an intermediate behaviour between a solid-like and liquid-like material.

Finally, a hysteresis curve was obtained by performing a Temperature-sweep of our polymer. The latter consists of heating the material up to 250°C, cooling it down to 190°C and reheating up to 250°C to see how the storage (G') and loss (G") moduli of the polymer respond.

This hysteresis behaviour suggests that when we heat up again our sample, extra energy (T°) is needed to go back to our initial state. Indeed, additional heat needs to be provided in order to soften/melt again the sample.

From what we know from a typical hysteresis trend, if we heat our sample up to 230°C and we wait long enough, we'll shift from the lower part to the upper part (---->) of the hysteresis.

So this information could be useful to prepare our material for printing since we are able to change the material's properties by the way we prepare our sample.

Conclusion

ColorFabb_HT is a strong 3D printer filament which is extremely durable and resistant to both physical impact and heat, able to withstand temperatures of up to 100°C (=Tg). When heating at higher temperatures, the filament becomes quite sensitive towards heating and starts losing its glassy properties.

Most of the above characteristics match the requirements for the rigid part of our final object to print in terms of flexibility, optical aspect (transparent) and mechanical except for its resistance to heat which is still too low (100°C).

Furthermore, this printing filament was quite difficult to print because of considerable warping/shrinkage occurring during our printing test and hence can be a real issue when printing some pieces.

Considering all the above reasons, ColorFabb_HT doesn't seem the most appropriate polymer for our project. And this is mainly due, as for nGnen ColorFabb, to its inability to withstand a temperature of 120°C.

By Robin