Plastic additives for re safety with weight reduction, thermal stability in processing and waste management Morpholino-poly(piperazinyl-morpholinyl-triazins)*

This paper is not just about the benets of the smart plastics, but also about the potential remedies of the environmental concerns of their use. It is also a discussion about a potential pathway to an ecient use of fossil (combustion) fuels and the reduction of the emissions caused due to their use, in general. Morpholino-poly (piperazinyl-morpholinyl-triazin) imparts sustainable re-safety and subdued incineration behaviour to plastics combined with weight reduction, and facilitates their melt processing. Additionally, it enables their ultimate environmentally friendly disposal as waste, after the ultimate use, coupled with simultaneous generation of usable energy. The knowledge & experience thus gained from energy extraction of waste plastics provide guidelines for future research to increase the eciency of energy extraction and the reduction of emissions from combustion fuels in general. The technology is also intended to safeguard against open burning of plastics that leads to air-pollution ashover and forest res. The various aspects of the experimental data generated are presented and plausible mechanisms of the technology are discussed.

increase the e ciency of energy extraction and the reduction of emissions from combustion fuels in general. For, much of the energy generated from combustion fuels is lost/wasted in combustion gases & emissions.
To contribute towards the resolution of the said issues, MCA technologies GmbH in Switzerland has developed morpholino-poly(piperazinyl-morpholinyl-triazins, a multifunctional technology that on one hand provides safety in melt processing and imparts a sustainable re-safety-in-use to plastics, combined with weight reduction, for the sake of energy saving in mobility. On the other hand, it enables their ultimate environmentally friendly disposal as waste, coupled with e cient generation of usable energy.
Materials Discussion: Fire-Safety: For the re-safety while-in-use of plastics, morpholino-poly(piperazinyl-morpholinyl-triazin) (PPMT-HF, I), is of particular interest as an environmentally friendly universal re retardant synergist that reduces the usage of the re retardant additive. Moreover, it suppresses the formation of smoke & toxic gases in the event of re [23], and enables "cold-incineration" of the waste plastics.
Depending upon the chemistry of the primary re retardant of choice to be used in combination, such re retardancy is provided either by char formation (the so-called intumescence) and/or by the formation of ceramic nitrides/oxynitrides at the re point, preventing the proliferation of the re. Formation of potentially hazardous gases is thereby either suppressed due to the exceptionally slow rate of burning at lower temperatures (cold-incineration), enabling systematically their capture as nitrides/oxynitrides and other derivatives of the re retardants in use. This unique synergism particularly reduces the total requirement of the re retardant addition for any speci c purpose. Although less e cient, PPMT-HF itself acts as a re retardant, due to the formation of some carbon nitride material [24].
The pictures of the residues at the points of re ignition/extinction, in a typical re test (Limiting Oxygen Index; LOI) [25], are shown in gures 2a-2d. enough for many re safety purposes of plastics. In addition, economy, processibility, recycling and environmentally friendly ultimate waste disposal make such plastics most sustainable of all other options.
The combinations of morpholino-poly(piperazinyl-morpholinyl-triazin), PPMT-HF, with the mixture of metal hydroxides and carbonates usually seem to be more e cient than with the corresponding individual components. Liberation of water from metal hydroxides during the combustion facilitates the capture of carbon monoxide, carbon dioxide and other acidic gases by metal hydroxides, thus reducing their emissions. On the other hand, self-immolation of PPMT-HF with triazine ring acting as a template for the formation of ceramic nitrides/oxynitride as re barriers such as shown in Fig.3 [26]. It is obvious therefore, that none of these individual components would be as effective on their own.
The formation of a mushroomed, red colored re residue with combination of poly(piperazinylmorpholinyl-triazin), PPMT-HF, magnesium dihydroxide & kaolin (Fig 2c), never observed before, is perhaps due to the formation of some unique hybrids of nitrides/oxynitrides.
Ammonium polyphosphate (APP) as a re retardant undergoes decomposition to phosphoric acid in the event of re, causing charring of the polymer and re retardancy at the re point. However, in the presence of morpholino-poly(piperazinyl-morpholinyl-triazin), PPMT-HF, phosphoric acid thus liberated reacts partially with PPMT-HF to form ultimately phosphorus oxynitrides as additional re barriers (Fig. 2d). The chemistry of the chain reactions perhaps occurring in situ during the re process is depicted in Fig. 4.
"The cone calorimeter has become one of the most important and widely used instruments for the research and development of re retarded polymeric materials" [27][28][29] . Thus, in our cone calorimetric study it is observed that in case of the polypropylene composites PP/10IS and PP/20IS containing 10% and 20% of the re retardant: Ammonium Polyphosphate + PPMT-HF, the peak ux (kW/m 2 ) of heat release is considerably reduced, the rate of burning considerably prolonged (Fig 5a), and the smoke formation appreciably diminished (Fig 5b). Ammonium polyphosphate alone, unable to form nitrides, is less effective as a re retardant, and also thermally less stable (Thermogravimetric Analysis TGA [34], Fig  7a) The combinations of morpholino-poly(piperazinyl-morpholinyl-triazin), PPMT-HF, with phosphinates such as Aluminium diethyl phosphinate (the major component of Exolite 1230 [30][31][32], also seem to ultimately provide ceramic phosphorous oxynitride ( g. 4), IV and V) as re barriers. Polymethyl methacrylate (PMMA), also known as "PLEXIGLAS", is a material used extensively for protective barriers to prevent the spread of corona virus. Being highly in ammable, use of non-re protected PPMA is a re hazard. Moreover, the ultimate disposal of the contaminated PMMA could also be an issue to be considered. Spectacular is not only the reduction of heat release in the event of re but also the least smoke production with PPMT-HF (MCA-HF) alone. We believe this to be due to the capture of graphene, contained in the black smog produced in the burning of PMMA, by carbon nitride, formed simultaneously from PPMT-HF in the burning process [25]. Evidence of this assumption is provided by the TGA analysis of the corresponding samples (Fig 6b). Whereas PPMA and MCA PPM-HF on their own are completely consumed in TGA analysis, with 100 % weight loss and 0 % residue, the residues of the TGA analyses of the composites of PPMA containing PPMT-HF vary between 8-12 %. . Reduction of the smoke release also seems to be directly related to the content of PPMT-HF in the composite.

Thermal Stabilization & Processing/Recycling:
Most Surprisingly, it is found that morpholino-poly(piperazinyl-morpholinyl-triazin), PPMT-HF, additionally acts as a heat stabilizer of polymers, beyond anti-oxidants, to retard visible and invisible degradation during melt-processing and reprocessing (recycling/upcycling) of invariably high-loaded (and heat sensitive) phosphorous containing re retardant composites.
Thus the thermal stabilization with PPMT-HF of polypropylene containing ammonium polyphosphate + PPMT-HF, in air atmosphere and under nitrogen atmosphere is shown in g 8a respectively 8b. Particularly to be remarked is the difference between the air atmosphere and the nitrogen atmosphere. In air atmosphere, the TGA graphs of the composites fall apart, due to the thermal stabilization granted by PPMT-HF both to the polymer as well as to the re retardant.
Under nitrogen, there is no oxidative thermal degradation of the polymer to be expected and hence the T onst of the polypropylene itself is distinctly higher (422 0 C vs 271 0 C). However the composites PP/10IS and PP/20IS containing 10% and 20% of the re retardant system show lower T onst (413 0 C & 399 0 C) corresponding to the lower thermal stability of the re retardant itself. The presence of PPMT-HF still seems to in uence slightly both T onst & T max , over and above the already much higher thermal stability of all composites under nitrogen.
The improved thermal stabilization of one of the most di cult to process glass-lled PA 66 composite containing aluminium diethyl phosphinate (i.e. Exolite OP 1230, Clariant) as the primary re retardant, and used extensively as an engineering polymer, is illustrated in Fig. 8.
The temperature difference in TGA analysis between the state-of-the-art combination of Exolite OP 1230 with melamine polyphosphate and now the most stable combination of Exolite OP 1230 with PPMT-HF is almost +82 0 C. This distinct difference is particularly due to the inertness of PPMT-HF towards the polymer itself. Besides getting decomposed melamine, salts are known to cause degradation of polyamides in melt-processing [35], and induce corrosion of the processing equipment.
Effect of PPMT-HF on the thermal stability of PMMA composites is seen in Fig. 6b. (+25 0 C).
PPMT-HF also reduces the rate of decomposition of thermal sensitive llers such as calcium carbonate or kaolin (Fig 9 ) in polymers: No matter in what polymer and in what combination we tested, we always found the thermal stabilizing effect.

Mechanism Of Thermal Stabilization
Stabilization is perhaps imparted due to heat energy absorption by the principle of boat-chair switching of the piperazine and morpholine moieties of the molecule in melt processing, with rigidity being provided by the at heterocyclic rest, without over-stressing the covalent bondings within the basic structure. This "Flip-Flop" mechanism of thermal stability due to PPMT-HF as illustrated in Fig 10 is  Plastics are fundamentally solid fuels, mostly derived from naturally occurring combustible materials such as fossil fuels or even the naturally growing or arti cially grown renewable materials. Of all the alternatives available, the most logical procedure of their disposal-after-use should be by incineration in closed systems. In this process, it should be possible to generate useful energy as well. The complex separation of different types of plastic for reuse as low-quality secondary raw materials, which also need to be ultimately disposed of, would not necessarily be required. The environmental and health impacts of waste incinerators strongly depend on emission control technology, as well as incinerator design and operation, but above all, on the composition of the waste, that needs to be strictly regulated. Use of plastic additives and colorants that can generate toxic substances upon incineration must be restricted.
In many countries, open burning of plastic waste is of great environmental concern. It is important, therefore, that open waste burning of the plastics is made inherently di cult, if not impossible, since such open burning causes direct release of toxic emissions in the atmosphere and danger of the spread of res.
For a safe, environmentally friendly (generation of less pollutants, especially nitrogen oxides and other toxic volatile materials, prevention of open burning) and an e cient energy generation during incineration, the combustion process must be inherently controlled (i.e. rather than "Molotov cocktail" like explosive ammability, slow but steady heat-release), and needs to be conducted at lower temperatures (cold-incineration) to ensure e cient energy capture, and particularly to avoid energy losses in combustion gases.
Although the potential re hazard of plastics is known almost ever since plastics exist, the focus has been on the re safety for some specialty purposes of their use. The focus of the present investigation is on safe and sustainable disposal of the plastics including energy extraction, with the aid of suitable re retardancy.
We, therefore, propose that certain minimum requirement of re retardancy should be extended to all plastics to enable their safe-incineration accompanied by e cient energy extraction as waste after-use. Such re resistance can also prevent their open burning, at any time.
The aspects of recycling and ultimate fate of plastics thus need to be borne in mind from the very beginning of their conception.
We are of the opinion that morpholino-poly(piperazinyl-morpholinyl-triazin) (PPMT-HF) could be a facilitator not only in recycling/upcycling due to its thermal stabilizing effect, but also for environmentally safer ultimate disposal and energy extraction from waste plastics.
As an example, Figures 11a-c show the cone calorimeter results ( ux 50 kW/m 2 ) of the polypropylene composites discussed above under "Fire Retardancy (LOI Fig. 2a-Fig. 2c) for the characteristics of their incineration behaviour, particularly for the disposal after-the-us.
Whereas the polypropylene alone (Fig. 11a) shows a peak heat release of 880 kW/m 2 and a total burning time of < 500 seconds (Fig 11b), the re retarded samples PP14 and PP8 show the peak heat release rates of < 125 kW/m 2 (Fig. 9a) and a burning time of over 1100 seconds (Fig 9b) . Of particular importance is also the less smoke production (Fig 11c), relevant for the emissions of toxic gases. Lower controlled incineration temperature ensures e cient energy extraction with less energy losses in combustion gases of P14 and PP8.
We have carried out similar studies with many other major polymers of commercial importance, with similar results. Chemistry/Technology:

Composed of C, H, N & O elements and characteristically insoluble, like an organic pigment,
MCAT-HF does not bloom out or bleed during the service life of the polymers, a necessary requirement of all polymer additives. The unique multistep process of its production is summarized in gure The technology is particularly characterized by the strategy that: a) no dendrimeric (only linear chain) polymers are formed [46], for the sake of ease of dispersibility in the substrates; b) for the ecology considerations, no solvent is used In any step of the synthesis; c) uniform sub-micron particles are formed in situ to facilitate their later on incorporation into the polymer metrics; and d) the end-product does not contain any residual halogen as the terminal end-group to meet the newer regulatory requirements.

Physics:
Particular characteristic of the technology employed is the fact that small sub-micron particles (< 1 um) of regular diamond shape and size are directly formed in the synthesis, requiring no further engineering manipulations to make their ease of incorporation and ne homogeneous distribution in the polymers.

Conclusions
PPM Triazine technology on one hand imparts sustainable re-safety-in-use coupled with weight reduction, and provides safety in melt processing to plastics, and on the other hand, it enables their ultimate environmentally friendly disposal after-the-use, coupled with e cient extraction of usable energy. The knowledge & experience thus gained from energy extraction of waste plastics could provide guidelines to increase the e ciency of energy extraction and reduction of emissions from combustion fuels in general. For example, it might perhaps be possible to impart fuel consumption e cacy of gasoline to the levels of diesel fuel for similar performance.
The technology is also intended to safeguard against open burning of plastic waste that causes pollution, and can lead to uncontrollable ashover and forest res.
Even if not incinerated, use of hydrophilic and/or acid-sensitive re retardants (such as phosphates, metal oxides and carbonates) could accelerate degradation of plastics in land lls, waterways and in the nature (accounting for almost 79% of the plastic waste) by environmental degradation.
The breakthrough of this concept, however, hangs substantially from relevant legislations, voluntary constrains and the demand of the public for such concepts. The recycling and waste disposal aspects of plastics thus need to be borne in mind from the very beginning of their conception.

Experimental conditions and test methods:
Procedure A : The materials were dry-blended in the required proportions and extruded using the twin screw co-rotating extruder Leistriz 18-40D as per the required experimental conditions described in [45] . The resulting granulates were pressed to samples of different sizes and subjected to various tests such as cone calorimetry [27][28][29], LOI [25], UL-94, TGA [34] & other tests as per the test standards, described in the text above.
Procedure B: Polymer pellets were mostly melt-mixed with the different additives in an internal mixer apparatus (HAAKE) at 190 ˚C and 80 rpm for 6 min. PA66 blends were, however, prepared using this machine at 280 ˚C and 60 rpm during 6 min. All blends were grinded and then hot pressed and molded using an Agila machine under 60 bars at 240 ˚C during 6 min for most blends and 80 bars at 190 ˚C during 8 min for PA blends, to obtain the specimens in the form of sheets. Samples of various sizes were obtained according to the cone calorimetry [27][28][29], LOI [25], UL-94, TGA [34] & other tests as per the standards described in the text above.
For comparison, the blank polymer samples were prepared using the same procedures.

Author:
Former global head of Pigment Technology Research at Clariant, the largest pigment producer worldwide, with over 50 years of work experience, and over 75 Patents. Dr. Kaul has invented, from conception to commercialisation, many new chemical moieties, given lectures at many scienti c and technical conferences world-wide, educated doctoral and post-doctoral students at ve different universities in GB, USA, Canada & France, made numerous research publications and is author of chapters in many handbooks.   Chemistry of the re retardancy with phosphorus-triazin systems    Chemistry and technology of morpholino-poly(piperazinyl-morpholinyl-triazin) (PPMT-HF) Figure 13 SEM picture of PPMT-HF: sub-micron, diamond shaped individual particles