Posts Tagged ‘polyimides’

Nexam Chemical Holding AB develops, manufactures and markets crosslinking chemicals for the polymer industry. The company is listed on NASDAQ OMX First North (ISIN SE0005101003, ticker symbol: NEXAM). 

CESI: A very interesting quote from the brand new Nexam patent application background section:

“PEPA, PETA and MEPA, the triple bonds will eventually react and cross-link to provide a cross-linked polymeric material, whereby improving the heat and chemical resistance, as well as the mechanical strength of the material. Using PEPA will require a heating to at least 350°C to cure the PETI (cf. US 5,567,800) and even somewhat higher, i.e. 380 to 420°C, to cure PEPA end-capped polyimides (cf. US 5,493,002).

However, for some applications such a high curing temperature profile may be considered a problem. For instance, the properties (such as the coefficient of thermal expansion) of flexible polyimide films, having a melting temperature below 350°C, may be improved via cross-linking. However, the high temperature (above 350 °C) needed to initiate cross-linking will make the processing impossible. Further, also for economic reasons the possibility to lower the curing temperature and/or increase the curing rate may be advantageous. Often such polymers are still to be processed above 300°C. PEPA may accordingly not always be replaced with an alternative cross-linker, e.g. MEPA, in applications requiring a lower curing temperature or a higher curing rate. Further, PEPA has the advantage of withstanding processing temperatures up to and even above 300°C without curing being initiated.

A process for modifying the curing temperature profile of PEPA-based system would thus be highly interesting, as it would allow for processing of “inert” acetylenical polymers, which subsequently may be activated and cured at temperatures tolerated by the molecular backbone.

As already described also acetylenical cross-linkers for thermoplastic polymers are available in the art. Thermoplastic polymers are processed in a wide temperature span above their softening point (Tg or melting point), but below their degradation temperature. It is often desired to affect the thermal curing behavior within this window to mirror/suit the process or parts manufacture. Especially, semi-aromatic polyamides end-capped by PEPA, as well as PA46 and PA66 end-capped by PEPA, represent types of acetylenical polymers, which would benefit from an altered thermal curing behavior.”


CESI: A very interesting quote from the brand new Nexam patent application Embodiments section:

“Upon continuously increasing the temperature of a composition comprising an acetylenical cross-linker, such as a polyimide end-capped with PEP A, the carbon-carbon triple bonds in the system will eventually start to react with each other. The cross-linking is believed to include a sequence of exothermic reaction steps, including chain-extension, probably due to ethynyl-to-ethynyl reactions, of the material and subsequent cross-linking, probably due to pericyclic reactions, e.g. Diels- Alder reactions and ene -reactions. Typically, the curing temperature profile may be studied by differential scanning calorimetry (DSC), as well as melt rheology measurements. DSC will provide information regarding the temperature required to initiate curing, while melt rheology will provide insight into the curing onset as well as into the degree of chain-extension and cross-linking, as such reactions will increase the viscosity of the material.

The melt viscosity of a polymer affects its processablity. A too high melt viscosity will make it difficult to process the composition, as the shear forces to generate sufficient flow will be extremely high. Thus, polymers are often processed at temperatures well above their softening point (glass transition temperature – Tg – or melting point – Tm). An increased processing temperature results in lowered viscosity, which may facilitate processing. However, the degradation temperature for the polymer of concern sets an upper limit for the processing temperature. Thus, polymers are processed at temperatures in between the softening point and the degradation temperature.

In processing and curing of compositions comprising an acetylenical cross-linker, not only the temperature required for initiating curing, but also the curing rate is of interest. Provided that the curing rate not is too high, some curing may be tolerated already during processing without rendering further processing, such as extrusion and injection molding, impossible.

As can be seen in FIG. 1, a peak corresponding to exothermic heat flow, i.e. curing, is seen upon continuously increasing the temperature of an oligomer end-capped with an acetylenical cross-linker. The exact shape of the peak, e.g. the temperature at which cross-linking is initiated and completed, as well as the temperature curing maximum, will depend on the temperature ramping profile applied. While the temperature at which cross-linking is initiated in principle is constant, the shape of the exotermic peak will, at least partly, be affected, by the temperature ramping profile applied.

The curing temperature profile of different acetylenical cross-linkers is different. In general, the chemical groups next to the carbon-carbon triple bond will through electronic and steric effects determine the curing temperature profile.

Furthermore, the mobility of the system of which the acetylenical cross-linkers is part, will affect the curing temperature profile, but to less extent. As can be seen from FIG. 2 the curing temperature profile of low molecular weight PEPA end-capped phenylene diamine, a model system for studying curing of PEPA, is similar to the one of oligoimide end-capped with PEPA (cf. FIG 1).

The present inventors have surprisingly found that combination of PEPA on one hand and MEPA on the other provides systems having another thermal curing behavior than the two individual cross-linkers if cured separately (cf. FIG 3). While the onset temperature for the curing is approximately the same, DSC-scans indicate that the curing mechanism is another. Especially, the curing of PEPA is completed at significantly lower temperatures and the curing of MEPA, from one perspective, seems to require higher temperatures to complete. The relative molar amount of the two cross-linkers will affect the thermal curing behavior.

Further, as can be seen from FIG 4b exchanging the cross-linker on the polymer does not affect the ultimate melt viscosity. However, the onset of the viscosity increase is shifted and the time required to attain the ultimate viscosity is prolonged. The somewhat higher initial viscosity for the PA-MEPA compared to the PA-PEP A indicates that some curing of MEPA has taken place already during compounding of PA-MEPA. FIG 4c shows that it is not as effective in this case to exchange the cross-linker of the oligomer/molecule as it retards the reaction too much for the specific example. The high initial viscosity for the PA-MEPA//HD-MEPA compound indicates that curing of MEPA has taken place already during compounding of the system.

As can be seen from Fig. 5, it was possible to affect the curing rate also in an acetylenical, semi-aromatic polyamide, i.e. PEPA end-capped PPA. Replacing HD-PEPA with HD-MEPA increased the curing rate (measured as pressure build up) of PPA-PEPA. Replacing also the end-capper, i.e. PEPA, with MEPA resulted in vary rapid build up of pressure, indicating that curing of PPA-MEPA//HD-MEPA at 340°C is rapid process.

Thus, it has been revealed that combined use of two distinct acetylenical cross-linkers, having different thermal curing behavior, provides a way of altering, and in some applications even tuning, the thermal curing behavior for a given polymer.

Accordingly, such combinations may be used to provide system with cross-linkers having thermal curing behavior adapted to suit that processing temperature and degradation temperature of concern.”

The full patent Source link is attached here


Best regards, CESI

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. 

This Nexam article primarily aims to highlight the improvement of material properties gained by applying Nexam cross-linking technology:

“Nexam develops crosslinkers that fit optimally into different kinds of polymers including polyimides, nylon, polyethylene, polypropylene, polycarbonates and PEEK. The technology, which is based on previous developments carried out by NASA, has now been further developed and new patents have been applied for. The new crosslinkers result in improved processing properties such as controlled melt behaviour and they can be tailored to work with almost any polymer.


“Formerly, fillers were used predominantly to cheapen end products, in which case they are called extenders. Among the 21 most important fillers, calcium carbonate (CaCO3) holds the largest market volume and is mainly used in the plastics sector.[2] While the plastic industry mostly consumes ground calcium carbonate the paper industry primarily uses precipitated calcium carbonate that is derived from natural minerals.” Source link, Wikipedia

Effect of temperature and filler. A few CESI conclusions:

Nexam demonstrates an example that a plastic´s tensile strenght is lowered ( – 33 %, at 210 °C ) when dilued with 60 % (mass weight) of calcium carbonate (CaCO3). However, for the same plastic crosslinked with 2.5 % of Nexam cross-linker, the plastic´s original tensile strength is retained even if “diluted” with ~60 % (mass weight) of CaCO3 (!)

Furthermore, in the same example at 210 °C, the cross-linked plastic (containing 2.5 % of Nexam cross-linker) is stronger compared to the original plastic (not containing Nexam cross linker), even if diluted with 10 % CaCO3 (+>40 MPa tensile strenght versus +>30 MPa tensile strenght in the highlighted example).

Source link (t =19:20, in Swedish): ref:



PE100 is an ISO designation for a grade of pressure rated PE material. The designation means simply that the material is polyethylene, PE, and that the material qualifies for a 10 MPa (100 bar, 1450 psi) MRS rating at 20°C Source link, 

For PE pressure piping materials, slow crack growth (SCG), is the long term failure mode. SCG is not brittleness. Stress such as internal pressure causes cracks to develop and grow through the pipe wall from stress concentrations Source link, 

Japan Polychem Corporation (wholly owned by Mitsubishi Chemical Corporation) claims that:

“Polyethylene, especially PE100 Resin has been steadily increasing its use in pressure pipes for water and gas based on its superior property balance. Of all the properties required for PE100, when we consider the defects on the pipe surface and the stress concentrations on the fitting of complicated shape, the most important for the lifetime of pipe should be the resistance to Slow Crack Growth (SCG). Recent requirements for cost reduction by no-dig or no-sand installation have been enhancing the need for the improvement of SCG resistance”


“Polyethylene(PE) has already established its position as a major material for many pipe applications,
such as gas and water distributions (pressure pipes), sewerage, drainage and conduit, based on it’s
excellent characteristics such as light weight/ flexibility for easy handling and chemical stability for
corrosion resistance. The strength of PE pipe line system to the earthquake according to its ability to
follow the ground movement and excellent fusion-welding strength is now well acknowledged. In
Japan, there have been several strong earthquakes with the magnitude of more than 6 such as the
Great Hanshin-Awaji earthquake (Magnitude 7.3, 1995) and the Niigata-ken Chuetsu earthquake
(Magnitude of 6.8, 2004). Although there were a lot of damages observed to iron, steel and PVC
pipes in those earthquakes, there was no report of the damage to the PE gas and water pipe line
system. Therefore, the usage of PE pipes to the lifelines like water and gas is increasing year after
year also in Japan.”

PE for pipes, especially PE100 resin, has been steadily increasing its use all over the world and is
expected to grow further. Together with the spreading of PE100 resin, the requirements for cost
competitive installation methods like no-dig or no-sand methods are also increasing. In these
installation methods, however, we can not avoid the surface defect by scratching and the
concentrated local stress by stone or something like that in the backfill material. These defect and
stress concentration can give the pipe more stress than anticipated and may cause the failure of the
pipe, if the material’s resistance to stress crack or slow crack growth (SCG) is not strong enough.”

Source link:

In the most recent Nexam presentation, the CEO Anders Spetz presented that SCG for PE100 pipes containing Nexamite equals a 307 % improvement compared to PE100 pipes containing no Nexam cross linker (reference). 

Source link (t =19:40, in Swedish): ref:



Hydrostatic testing is universally known and accepted as the primary means of demonstrating the fitness for service of a pressurized component (Source link, Plastic Pipe Institute)

  • An indoor video example of a hydrotest

  • An outdoor video example of a hydrotest

Hydrostatic leak tests typically use cooler liquids so the liquid filled test section will tend to equalize to a lower temperature near test liquid temperature. Source link, Plastic pipe 

In the most recent Nexam presentation, the CEO Anders Spetz also presented results from a hydrotest. PE100 pipes containing Nexamite equals a 320 % improvement compared to PE100 pipes containing no Nexam cross linker (reference).

Sourcelink, Nexam at småbolagsdagen 2015 (In Swedish, t = 19:40)

PE pipe status note, Nexam 2014 Annual report: Other promising partnerships Other promising partnerships include PE applications (polyethylene), in which full-scale testing will be conducted by pipe manufacturers during the first six months of 2015. The aim is to develop a manufacturing process using crosslinkers from Nexam Chemical that results in plastic pipes with greater stability. This would enable the manufacture of pipes in larger diameters, while maintaining production speed


Du Pont:

“There is a need for a new method for making polyimide nanowebs with suitable mechanical properties from high concentration solutions; polyimide nanowebs comprising nanofibers of a cross-linked polyimide; separator comprising polyimide nanowebs; and multilayer articles and electrochemical cells comprising separator.”

In  this patent, Du Pont demonstrates that mechanical and electrical properties were improved using the Nexam products EPA (ethynyl phthalic anhydride) and PEPA (4-phenylethynylphthalic anhydride)! Additionally, Du Pont specifically states that PETA was obtained from Nexam (WO 2013/181333 A1; E. I. DU PONT)

Addition Curable Polyimides – Summary from the Nexam – Evonik Webinar


•Increased coating build and / or line speed
•Removal of solvents
•Controlled thermal activation


•Retention of properties at high temperatures
•Solvent resistance
•Low void content

Source link: Nexam Evonik Webinar.

IMPORTANT NOTE : Webinar available only until September 24, 2015 (!)

A new Nexam resin: NEXIMID® MHT-R in short Source link

Nexam Chemical introduces a new ”easy to process” resin that is primarily intended for use within the aerospace industry. Other areas, such as machine, general industry and transport sectors will also benefit from this high property material. The new resin, NEXIMID® MHT-R, is intended for small to medium sized production volumes of high-temperature composites by Resin Transfer Moulding (RTM). Temperature properties such as Tg is superior to most other materials and polyimides on the market.

  • Binders for fixation of fibre preforms:
    Reactive binders for fixation of a fiber pre-form are available. The binders are NEXIMID® A57 and A58.  A57 is a mono functional binder that reacts with the resin and A58 is a bi functional binder. Each binder melts at a specific temperature and upon cooling glues the pre-form together. During processing the binders react with the resin upon curing. The reaction is an addition reaction and no volatiles are formed during the process.


From Nexam patent US8492507 B2 Source link 

“Polyamides are recognised as exhibiting good abrasion resistance, low friction coefficient, good resistance to heat and good impact resistance. Polyamides are in dry conditions good electrical insulators. Polyamides are typically hygroscopic and absorb water. This absorption will change some properties, such as insulation, tensile strength and stiffness. The impact resistance is increased by a higher content of water.

There are, despite the fact that polyamides have excellent physical and chemical properties and for a long time have been widely used for resins, films, fibres, moulded articles and so on, demands for improved and/or modified properties, such as increased operational temperatures and retained properties during and after exposure to for instance harsh temperature, atmosphere, mechanical and radiation conditions.

It has now quite unexpectedly been found that an acetylenic polyamide can be obtained by incorporation of one or more carbon-carbon triple bonds into a polyamide, for instance as endcapping group(s), as pendant group(s) along the molecular backbone and/or as group being part of the molecular backbone. The acetylenic polyamide of the present invention meets said demands for improved and/or modified properties exhibiting an excellent combination of toughness, resistance and thermooxidative stability” […]

The purpose of the present invention is to modify the mechanical properties of polyamides and compositions comprising polyamides. Among these modifications of properties can be mentioned: higher softening temperature, higher E-modulus and improved ability to counteract creep strain.

Note: E-modulus = Elastic modulus =  A number that measures an object or substance’s resistance to being deformed elastically (i.e., non-permanently) Source Link, Wikipedia


PET bottles exposed to UV light negatively impact next generation bottles – Plastic Engineering

Described above is a “storage issue” of PET bottles produced from recycle material. In fact, Nexam might potentially already have principal solutions at hand to this issue, both in respect to chain extenders (= PBO = “repair agents”), UV protection during second generation production of recycled PET (see bold font below) and the original and new Nexam cross linking approaches (see bold font below). One example:

  • Nexam patent US20140018460 – COMPOSITIONS FOR IMPROVING POLYESTERSPublication Date:16.01.2014


“Accordingly, the present invention preferably seeks to mitigate, alleviate, eliminate or circumvent one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solves at least the above mentioned problems by providing a method for altering the melt characteristics, such as the melt strength, of a polyester.” […]

“According to an embodiment, also blowing agent, such as carbon dioxide, nitrogen, alcohols, ketons, methyl formate, hydrofluorocarbon a hydrocarbon, e.g. n-hexane, iso- or n-pentane, cyclopentane and n-heptane, or a gas mixture thereof, an expanding agent, a foaming agent, nucleating agent, such as talc, kaolin, silica gel, and TiO2, 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 is melt mixed with the polyester” […]

“The cross-linker and chain extender comprising at least two groups being able to react with a carboxy group and a phenolic hydroxyl group will act as chain extender, e.g. by connecting terminal carboxy groups of two separate polyester molecules, as well as cross-linker, e.g. by connecting non-terminal pending carboxy groups of two separate polyester molecules. The molar ratio of polyester and tetracarboxylic dianhydride, will affect the number of non-terminal pending carboxy groups being present and hence also the degree of cross-linking. Further, the cross-linker and chain extender will act as water/acid scavenger, as any water in the material will result in hydrolyzed polyester generating an acid and an alcohol, these acids can be tide back to the polymers by the cross-linker and chain extender if such is present in the material.”

In fact, the above described cross linking approach is not based on the earlier reviewed and described 2+2+2 cyclotrimerization (the Berthelot reaction). This polyester cross linking approach is based on another type of chemical reaction. If time allows, CESI will describe this specific reaction in a more pedagogic approach that hopefully also can be understood by a non chemist.

Furthermore, the Armacell patent EP 2 163 577 A1 is refered:

“As taught by EP 2 163 577 A1, it is known within the art that a combination of PMDA (pyromellitic anhydride), PBO (1,3-phenylene-bis-oxazoline), and a sterically hindered phenol, i.e. a compound comprising a 4-hydroxy-3,5-di-tert-butyl-phenyl moiety, may be used to improve the properties of PET. The sterically hindered phenols are stated to be believed to act as hydrogen donor, wherein radical scavenger neutralizes the alcoxy or peroxy radicals generated by hydrolytic or thermal degradation, and does thus terminate the chain propagation of degradation processes. It also stated that, by adding sterically hindered phenols, the effectiveness of functional anhydride groups remain, therefore, intact for further upgrading reactions.”

“The present inventors have unexpectedly found that the addition of poly functional compounds comprising at least two non-sterically hindered phenolic hydroxyl groups rather than sterically hindered phenols, as taught be EP 2 163 577A1, improves the PET further. Further, the present inventors have also found that the non-sterically hindered phenolic hydroxyl groups may be replaced or complemented with carboxy groups.”

CESI Conclusions: A or B or C 

  • A: Nexam and Armacell is working closely togheter (= very positive)
  • B: Nexam is fully or partly taking the role as a sheer (successful) innovator in Armacell´s- and other competitor´s core PET research areas thereby securing IP and potential near future business value also within this segment (= positive)
  • C: Nexam aims to independently and additionally capitalize on the invention in PET areas not covered by the current PET foam exclusivity agreement (= positive, exlusivity agreement source link)

Is Armacell planning to purchase PBO (on scale) from Nexam? Was this a key driver for the recent Nexam PBO commercialization? Time will tell.

Best regards, C.E.S.I.

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.