Nylon 230 | mapr2016

Nylon 230 Taulman

Nylon 230 is one of the many types of nylon developed by the Taulman3D company for 3D printing. It has been specifically designed to print easily nylon. Indeed there is no need to heat the bed and it can be printed at the low temperature of 230°C. Its composition has not been shared by the manufacturer.

What is Nylon ?

Nylon is a semi-crystalline thermoplastic synthetic polymer. Indeed it is manufactured in chemical plants from organic materials such as oil or coal . Most of the time it is made by condensation polymerization which combines two molecules carrying carboxylic acid and amine groups. This reaction is industrially achieved using heat, at around 250°C and at moderate pressure. (you can click here to know more about the synthesis of nylon). [1] [2]

Figure 1 : Synthesis of Nylons by polycondensation [1]

Thus the reaction produces linear chains which are arranged parallel to each other, interacting by hydrogen bonds. This reaction can give rise to many different kinds of nylons including the most common ones : nylon 6,6 , nylon 6 or nylon 5,10. The numbers refer to the number of carbon in each monomer unit.

Physico-chemical properties of nylon 230

Mechanical Properties

Nylon 230 shows a high degree of flexibility while maintaining a high degree of strength. Indeed its competitive tensile strength of 73 MPa is higher than the 50 MPa of the ABS often taken as reference. Nylon 230 is also relatively light compared to the other available polymer with a density of 1.12 . . Another very interesting characteristic is its high resistance to abrasion making it ideal for mechanical joints with friction. [3] [5]

Thermal Properties

Due to high intermolecular forces Nylon is known as a heat-resistant material. A summary of the important characteristic temperatures of Nylon 230 can be found in the table below. [3]

Table 1 : Thermal Properties of Nylon 230

Other features

Although Nylon 230 generally resists well to chemicals and hydrocarbons it dissolves in harsher chemicals such as strong acids (here you can see the nylon resistance chemical chart). This can be very problematic since our pair of pliers should be used in chemistry research. [4] [5]

In addition Nylon 230 tends particularly to absorb moisture from the environment. This can significantly affect the mechanical properties of the material. The absorption of water can lower the strength and the stiffness while increasing the ductility of the material. [5] [6]

Application field of Nylon

Nylon is a polymer used in a countless number of applications for decades. The first toothbrushes and women's stockings were made in this versatile polymer.

Textile industry aside, it was used also in several different fields ranging from tennis racket strings, fishing lines and parachutes to cheap machine gears or machine screws.

Figure 2 : Parachute, gears and stocking can be made of nylon [7] [8]

The printing material

Nylon 230 filaments can be printed on most of 3D printers as it can be printed at 230°C and without heating bed. However it is a hygroscopic polymer and thus needs a previous drying. Otherwise water in the filaments can generate bubbles during printing which would diminish the layer adhesion and thus the performance of the material. Furthermore, when heated, nylon can also be hydrolyzed in a strong acidic environment. Indeed the rupture of the CO-NH bond breaks the long chains and leads to the formation of carboxilic acid. These phenomen deteriorate the surface of the sample as shown in Figure 3. [9]

Figure 3 : Dry nylon on the left, wet nylon on the right [9]

Another important issue relates to the fact that it cannot be printed easily as a dual material combination. It is due to the self lubricating and chemical resistance properties of nylon. Therefore it is recommended to print the raft in nylon itself. However the raft can sometimes be excessively hard to remove. To avoid this problem the model can be printed without raft and in this case, it is advocated to reduce the infill percentage and increase the temperature of the heating bed in order to minimize the risk of warping. [10]

For the support, Limosolve HIPS can be used but there are always important risks that the model moves on the HIPS material.

It is also necessary to cover the surface of the bed by blue tape. Recommended printing speed for the material is in the range of 30 - 50mm/s.

Experimental analysis

3D-Printing test

A printing of a dogbone-shaped sample was perfomed. The filaments were dried the night before in a vacuum oven at 60°C. The experimental conditions are described in the table below.

Table 2 : Experimental conditions for the printing test

First the printing was realised with a raft. Although the printing in itself was straightforward, the raft was very difficult to remove. Unfortunately the sample was seriously deteriorated during the removal process. This issue can be even more troublesome for more massive pieces.

A second printing attempt was made without any raft. The printing was also easy. However, as shown in figure 4, some warping can be observed. To completely eliminate it, the bed temperature can be increased up to 60°C.

Figure 4A : Printing test of the dog-bone shaped sample without raft

Figure 4B : Some warping can be observed

DSC

Nylon 230 filament was dried during the night before the experiment at 60°C . First a sample of 7 mg was heated from 25°C to 250°C. Then the sample was cooled to 25°C to finally be reheated to 250°C. These curves were performed at an average rate of 10°C per minute. We did not record any mass loss during the experiment.

Drying is necessary because moisture can act as a plasticizer that decreases the entanglement and the bonding between the molecules. If no drying is applied the sample has a lower Tg and Tm.

Figure 5 : Results of the DSC experiment : In black the 1st heating curve, in green the 2nd heating curve and in blue the cooling

link betwen time of rest & Tg

We can distinguish on both heating curves different downward peaks which are the signs of endothermic transition.

The first peak on the first heating curve at 63°C would correspond to a glass transition of the sample. However the jump in the curve which would illustrate the heat capacity difference between the glassy state and the liquid state is not really apparent. This is because of the polymer being so crystalline that the DSC does not have the required sensitivity to detect the Tg.

The peak translates the kinetic aspect of the glass transition. Indeed the drying process which was performed just below the Tg can be assimilated to the physical ageing of the glass.

Figure 6 : Illustration of the effect of physical ageing on the enthalpy [11]

When the sample was held at 60°C the glassy part attempted to reach a state closer to the stable state by eliminating excess of enthalphy. More specifically the polymeric chains tried to reorganize to reduce the specific volume of the sample. Therefore the sample underwent a slow isothermic contraction. When we heated the sample, at a temperature close to the specified Tg , the specific volume started to increase rapidly as well as the enthalphy resulting in an endothermic peak in the DSC. This peak is not anymore present at the second heating curve because the memory of the physical ageing has been erased with first heating.

Then the exothermic peak at 168 °C on the cooling curve correponds to the crystallisation of the sample. The molten polymer recovered its semi-crystalline structure.

Finally the peaks at 208 °C on both heating curves correspond to a melting point. It is suprisingly higher than the 195 °C expected. The area under the peak which represents the enthalpy of melting is directly related to the degree of crystallinity of the sample. We can also note that the peak spreads over a wide temperature range from around 171°C to 218°C.

Rheometry

The rheometry experiment was performed on a strain-controlled plate-plate rheometer. The samples were dried the night before the experiment at 60°C.

First we made a strain sweep to select the conditions that will allow us to stay in the linear viscoelastic region. In order to secure the experiment in the linear viscoelastic region, all following tests were made at a strain of 15.5%.

Then we made a frequency sweep at the recommended printing temperature of 230°C. We can estimate that the shear rate of the extruder in the 3D printer ranges from 1 to 100 . It increases with the flow rate and thus with the printing speed.

Figure 6a & b : Rheometry test - Frequency sweep performed at 230 °C

In these conditions, as we can see in Figure 6a, the sample started to flow as it passed the rubbery plateau. We can also note that the behavior of the sample is viscoelastic and thus the flow can not be assimilated to an ideal Newtonian flow. However as shown by the change of slope of the storage modulus, the sample started to degrade at low frequency and this made the results unreliable from this frequency.

If we extrapolate the curve to higher frequencies, the maximum of the storage modulus will not be very marked and will be relatively broad. So there is not a single time where all the chains relax. We have a very wide relaxation time spectrum. Thus, the sample is quite polydisperse.

Figure 6b shows also that the polymer is a shear-thinning fluid. According to Cox-Merz rule, this graph can be interpreted as the variation of the steady shear viscosity with the shear rate. Beyond 10 , the curve fits very well the power law model with a n index of 0.67.

Then we performed frequency sweeps at 220°C and 240°C. We see that the shift factor which follows the Arrhenius law (when we are far from the Tg) is very small between the different curves. It means that the empirical activation energy Ea (in the Arrhenius law) is very small. Therefore the flow properties vary little with the temperature. Note that the experiment at 240 °C was stopped at 0.5 rad/s because of thermal degradation.

Figure 7 : Frequency sweep performed at different temperatures

Figure 8 : Temperature sweep performed at 10 rad/s

Figure 8 shows the results of a temperature sweep at 10 rad/s. We clearly see that the loss tangent (the ratio between G’' and G’ which gives a measure of the viscous portion to the elastic one) does not vary much with the temperature. In this case the loss tangent is greater than 1 meaning that the sample tends to behave more like a liquid. The slight increase of the loss tangent at about 215°C would correspond to the end of the melting peak on the DSC curve.

We can conclude that changing the print temperature has not a very significant effect on the extrusion process. The maximum printing temperature of our 3D printer is 250°C, only 20°C beyond the recommended temperature. If we encounter a problem with the printing, in addition to increase the temperature, it might be worthwhile to diminish the printing speed. A successful printing was also made at 224°C just above the melting point as we can see on the DSC graph.

Conclusion

This report showed that Nylon 230 is particularly adequate for the rigid part of the pair of pliers. The DSC demonstrated that Nylon can withstand 120°C as the principal melting temperature is around 208 °C. In addition Nylon is strong, light and able to sustain abrasion to a certain level. So it is also an ideal material for articulated parts. The printing and the rheometry test showed also that other advantages of Nylon 230 are linked to the easiness of printing and to the relatively low temperature needed therefore. However we need to be careful as it absorbs moisture and dissolves in harsh chemicals.

By Alexis