Nexam Chemical: Superior Melt Strength of PETA-PBO formulations for PET, Nylon and Polyuretane, CESI comments new patent application

Posted: 28 November, 2017 in Nexam, Published Investment Calls
Tags: , , , , , , , ,

What Is thermoplastic polymers and in what ways are Nexam Chemical improving the properties of the materials? One methodology will be described in this blog post.

A multitude of our popular plastics are defined as thermoplastics which means that upon recycling , their molecular properties does not change as the plastic is melted and reused (according to definition and in theory). Examples are PE, PP, PTFE (Teflon), ABS and polyamide (nylon).

A very easily digested full pedagogic description is available here:

https://sciencing.com/thermoplastic-polymer-5552849.html

Another example of a thermoplastic is PET (polyethyleneterephtalate) which is used in composite sandwich constructions and light weight construction materials. The company Armacell is active in this business with sustainability in focus (recycling of PET bottles):

https://local.armacell.com/en/armaform-pet-foam-cores/

CESI has already highlighted that according to the Q2 Nexam Chemical interim report, Armacell will use Nexam proprietary technology in the next generation PET foam:

“The delivery agreement that we signed with Armacell last quarter is about to, with some delay, find its practical form. Armacell will use NEXAMITE® in its ArmaFORM® PET-foam to achieve increased efficiency” Source link. Statement found on page 2.

The explanation to the repeated CESI highlight is the following finding: A new Nexam patent application was published a few days ago (November 22, 2017). The described invention relates to a process for increasing the melt strength of a thermoplastic polyester and to mitigate degradation of the polyester during melting.

The common (?) degradation issues of PET is pedagogically described in this open access article by Venkatachalam et. al.:

“The main degradations that can occur include thermal degradation, oxidative degradation and hydrolytic degradation. Radiation induced or photo degradation leading to free radical reactions and enzymatic catalysed reactions leading to logical degradation are also possible. In addition to these there can be chemical degradation reaction of polyester initiated by specific chemicals like glycol, ammonia or amines or other such reagents. Besides these there can be weathering ageing which could be the combined effect of exposure to temperature, moisture, chemical, UV and visible light and other conditions such as exposure to grease, oil. Polyester can also undergo stress induced degradation reactions when subjected to mechanical stress. The degradation of polyester can lead to several changes in the articles made out of the polymer. These changes include discoloration, chain scissions resulting in reduced molecular weight, formation of acetaldehyde and cross-links or gel formation and fish-eye formation in films.
The thermal and thermo oxidative results in poor processibility and performance
characteristics in the products. Discoloration is due to the formation of various
chromophoric systems following prolonged thermal treatment at elevated temperatures.
This becomes a problem when the optical requirements of the polymer are very high, such as in packaging applications.”

Let´s look at some quotes from the following new Nexam patent application…

EP3246349 PROCESS FOR INCREASING THE MELT STRENGTH OF A THERMOPLASTIC POLYMER

Publication Date:22.11.2017

Applicant: Nexam Chemical AB

Source link here (most easily digested if downloaded)

“However, especially thermoplastic polyesters, but also to some extent aliphatic polyamides, suffer from having a narrow processing window, thereby typically requiring specialized processing equipment. This is related to the melt rheology of thermoplastic polyesters. Thermoplastic polyesters typically have low melt viscosity, low melt strength, and low melt elasticity.”

[CESI: see blue font below for “rheology” explanations]

“[0012] By using PETA, rather than pyromellitic dianhydride (PMDA) commonly used in the art, the melt strength of thermoplastic polyesters could be considerably increased. By use of the same combination, i.e. PET A and a bisoxazoline, also the melt strength of polyamides, e.g. aliphatic polyamides, and thermoplastic polyurethanes, could be improved.

[0013] Further and importantly, the rate of the thermomechanical degradation seen in melt mixing of thermoplastic polyesters was considerably decreased compared to PBO/PMDA-systems, as can be seen from Fig. 1. For applications with longer residence times, such as residence times exceeding 10 minutes, this is a clear advantage, as the thermomechanical degradation is quite rapid for PBO/PMDA-systems. A typical example of an application with longer residence time is extrusion foaming of PET. polyesters was considerably decreased compared to PBO/PMDA-systems, as can be seen from Fig. 1.

CESI:  Nexam specify a large number of polyester polymer substrates and additives:

“According to an embodiment, the thermoplastic polymer is thus a polyester. The polyester is typically an aliphatic polyester or a semi aromatic polyester. The polyester may be selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), 30 polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), and polyethylene naphthale (PEN). Specifically, the polyester employed may be a semi aromatic polyester. Examples of aliphatic polyesters include polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), polyethylene adipate (PEA), and polyhydroxyalkanoate (PHA), e.g. poly-3-hydroxyvalerate (PHV), poly-4-hydroxybutyrate (P4HB), and poly-3-hydroxy propionate (P3HP). Examples of semi aromatic polyesters include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene 35 terephthalate (PPT), polybutylene terephthalate (PBT), and polytrimethylene terephthalate (PTT). Further, the semiaromatic polyester may be a co-polymer of PET, PBT, or PEN.

Thus, also a nucleating agent, such as talc, kaolin, silica gel, orTi02, a flame retardant, such as a halogenated, charforming (like phosphorus-containing) or water-releasing compound, a plasticizer, a lubricant, such as an ester of a fatty acid, an impact modifier, insulation modifier, a pigment, a filler, an antioxidant, a UV-stabilizer and/or a color improver may be added to the thermoplastic polymer and melt mixed therewith.”

Fig 2 visualizes (see graph in link here) that…

At high frequencies> 100 rad/s (i.e. at high shear rate) the differences between the different formulations is relatively small, whereas at low frequencies <1 rad/s (i.e. at low shear rate) the complex viscosity of the PETA-PBO formulation is approximately at least one order of magnitude higher than the comparative examples. Further, the cross-over point, which was determined from the frequency sweep analysis, was significantly lower for Example 1 as compared to the Comparative Examples 1-4. Determination of cross-over point is a method used to evaluate the melt strength (ref J. Frankland, Plastics Technology Online 2013-05-28). Thus, the  melt strength of the PETA-PBO formulation is superior compared to that of the comparative examples. Further, this confirms that pressure in the extruder may be used as a semi-quantitative measure of the melt strength, as the shear rate in the current experiments is about 6 rad/s in the extruder

The claim comprehends a number of polymides: PA6, PA 11, PA 12, PA46, PA41 0, 50 PA66, PA61 0, PA612, PA 1010, PA 1012, and PA 1212.

[CESI: Again, a polyamide is equivalent to nylon: https://en.wikipedia.org/wiki/Nylon]

And interestingly, the following article are stated in the final section of the patent application as a “document considered to be relevant”:

https://www.ptonline.com/articles/additives-multi-purpose-modifiers-pump-up-properties-of-virgin-recycled-plastics

Furthermore, the Armacell patent EP 2 163 577 A1 is exemplified.

In the ptonline link attached above,  a very interesting picture demonstrating the (potential) impact of Nexam technology is found (Nexam treated polymer vs untreated)

About Rheology- the science of deformation and flow of materials

Explanation of the unit rad/s found in the Nexam Chemical melt strength comparison plot:

  • Wikipedia (“shear rate unit” search): The SI unitof measurement for shear rate is s−1, expressed as “reciprocal seconds” or “inverse seconds
  • Wikipedia (“rad/s” search): In physics, the angular velocity of an object is the rate of change of its angular displacementwith respect to time. The SI unit of angular velocity is radians per second.

CESI Conclusion: It´s simply the frequency/velocity of the flow expressed in a more complicated way. Thus, it should directly correlate to the speed of the extrusion (the continuous manufacturing of plastics)

The link below describes fundamentals of Rheology in a pedagogic way: http://www.polydynamics.com/Rheology.pdf

CESI Learnings:

  • The higher the shear rate, the easier it is to force polymers to flow through dies and process equipment.”
  • When a force is acting tangentially on a surface, the corresponding stress is referred to as shear stress. Normal stress (=normal pressure) = when a force is perpendicular to a surface
  • Viscosity = Shear stress / shear rate (= a higher shear rate equals a lower viscosity)
  • Shear rate = Velocity / h (hight in the case of flow through 2 planes)
  • With careful rheological measurements, it is possible to determine whether, or under what conditions, a material will be processable. Blend ratios, or additive quantities necessary to facilitate processing can be determined. Many problems can be avoided by a thorough rheological characterization, before the material is introduced into the extruder hopper
  • With careful rheological measurements, it is possible to determine whether, or under what conditions, a material will be processable. Blend ratios, or additive quantities necessary to facilitate processing can be determined. Many problems can be avoided by a thorough rheological characterization, before the material is introduced into the extruder hopper

CESI rheology conclusion: So, rheology tells us that increased velocity (flow speed) will generally be beneficial for polymer processing up to the point shark skin (surface mattness) and melt fractures occurs as described in the article above.

In this patent application, Nexam demonstrate how melt strength can dramatically be increased even during slower speed (frequences,velocities, rad/s) and slow speed seems crucial for PET foam production and most importantly: The improvement is substantial – a full magnitude at < 1 rad/s (see page 14 here). The X axis unit “rad/s” was explained above (= frequency/ velocity/speed of the extrusion)

Thus, it seems that Nexam has solved/improved the melt strength in the “difficult slow extrusion PET foam case” by adding to Nexam product molecules that in fact result in a synergy effect As the key is to keep a high melt strength for an extended period of time as described here in the Nexam patent application quote:

[0058] Whereas system comprising PMDA or combinations of PMDA and PBO also are effective in reacting with PET to increase the melt strength (measured as increased pressured in the extruder), these systems are prone to quite rapidly cause degradation. For longer residence time, such as the ones typically used in e.g. foaming application, the final melt strength is thus significantly lower (cf. Fig. 1 and Table 4). However, as can be seen from Fig. 1 and Table 4, systems comprising combinations of PETA and PBO, may provide increased melt strength also for longer residence times as the melt strength declines far less rapidly. As can be seen in Fig. 1 for the PMDA, PMDA+PBO and PBO formulations, 20 the pressure reaches its maximum value in < 10 minutes and after that, it decreases with increasing time. For the PETA+PBO, on the other hand, the maximum pressure is obtained after> 10 minutes. Also, for the PETA+PBO formulation the pressure at the end of the experiment is significantly higher than for the comparative examples

The opposite easy case is the following scenario described at page 3 here: http://www.polydynamics.com/Rheology.pdf

“One remarkable property of polymeric liquids is their shear-thinning behavior (also known as pseudo-plastic behavior). If we increase the rate of shearing (i.e., extrude faster through a die), the viscosity becomes smaller [….] This reduction of viscosity is due to molecular alignments and disentanglements of the long polymer chains. As one author said in a recent article: “polymers love shear.” The higher the shear rate, the easier it is to force polymers to flow through dies and process equipment.”

Best regards, CESI

(Not skilled in the art of polymer chemistry but with an ambition to continuously gain learnings…)

The author, Cutting Edge Science Invest, is a Nexam Chemical share holder. Cutting Edge Science Invest can not guarantee, or take into  accountability, the content of truth and accuracy of the information in this article/post.Thus, Cutting Edge Science Invest requires that a possible reader gather complimentary information if any type of investment in the company described above is considered. Cutting Edge Science Invest provides personally biased information and at best also “general information and opinions”. The article/post does not contain professional investment advice. 

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