Bio-based polyether diols offer high quality and performance from DuPont

DuPont’s new polyol is aimed at elastomers, TPU and coating but spandex fibres are also a target

What’s novel about DuPont’s new Cerenol range of high-performance polyether diols is not only that they are made from a renewable resource – the company’s Susterra 1,3 propanediol (PDO), produced via fermentation of corn sugar – but more importantly that they are high-quality products aimed at higher formance applications.

One of these uses, some way down the road yet, lies in spandex PU fibres, a product that demands exceptional quality and performance, DuPont executives told Urethanes Technology International, in a 6 Oct interview during the meeting of the US Center for the Polyurethanes Industry, in National Harbor, Maryland.

Another novel aspect of the diols is that they might never have seen the light of day had DuPont not divested a large business making a competing product, PTMEG (polytetramethylene ether glycol).

Typical PU outlets for DuPont’s new polyether diols are in elastomers, copolyether thermoplastic elastomers and coatings.

DuPont has been supplying samples from a “relatively small unit down in Mississippi,” said Ray Miller, Cerenol global business manager with DuPont’s Applied BioScience’s unit.

But it is now, “starting a commercial-scale unit,” Miller said, and will be making products available for “customers that are ready to go.” The new unit will make about 1000 tonnes initially, starting late December, Miller said. And as it is a batch process, “we can add additional reactors, we can go up to 20 million lb (10 kilotonnes) annual capacity,” he added.

DuPont has about 20 customers who have launched development programmes and some are ready to place orders. “We are selling product today,” Miller noted.

DuPont makes the PDO by fermenting sugars derived from corn kernels, at a $100- million joint venture plant operated with Tate & Lyle in Loudon, Tennessee.

The Cerenol team is excited at having reached this stage: and delighted that Cerenol gained an Innovation Award at the CPI event.

“We think coming out of this recession, people are ready for new ideas and technologies,” Miller continued. “Now we want to be visible, it’s time to make a splash,” he said, adding “We have some terrific underlying technology, thanks in large measure to Hari (Hari Sunkara, principal innovator for Cerenol),” who holds most of the patents.

Cost not bio-source was the driver

 “What I found interesting when I joined this group was the focus on the processes and on the quality of these materials that you could make from the bio technology route — rather than the sustainability aspect,” noted Maya Sethuraman, sales manager for Cerenol.

Miller said costs were always the priority, not the bio-materials route, although he paid tribute to Chad Holliday, the DuPont chairman at the time, for promoting bio-production routes.

Cerenol came about as DuPont looked for uses for an excess of its bio-PDO capacity. “Hari was the first one to try to polymerise it with itself and that worked very well,” said Miller.

This was surprising because, as Miller pointed out, “You can’t do this with the other glycols with two or four carbons. They cyclise so you can’t make a direct ether-linked polyol.” With three carbons rather than four between the ether links, Cerenol has “a lot more flexibility, much more chain mobility and that reduces the crystallisation phenomenon,” said Miller, “which allows you to make softer, tougher, more resilient elastomers.” With Cerenol, the condensation polymerisation is very flexible, “so you can make lots of different products,” said Miller.

“You can’t do that with ring-opening chemistry,” as used to make PTMEG, he said.

“And Hari discovered he could add new monomers into the backbone,” for polyols with very different properties. Also, “you can react the ends with fatty acids,” to make esters, with different properties, Miller said.

For the Cerenol homopolymer series, the main market is elastomers (see box below).

For copolymers, the G series with glycols goes into personal-care, cosmetic formulations, skin-care products while the E series with esters into functional fluids.

One of the benefits of Cerenol is its “very low toxicity. It is not a skin irritant and it is biodegradable ultimately,” Miller said. This makes it an easy material to deal with, the process is relatively easy to run, and no toxic chemicals are used.

Sunkara said one advantage of DuPont’s approach is that “We have no in-kind competition. This is the only polyether glycol molecule available on the market. It’s a new product and we have more than 100 patents on how to make it and how to use it.” Drawing on this strength, “we want to find more high-value end-uses,” he said.

Fibres offer good potential

 Looking five years ahead, Miller said his dream is that, “We will be building a very large facility next to a large bio-PDO plant somewhere in the world where there is cheap sugar.” And Sunkara chipped in with another aim: “We want to make Cerenol polymers for spandex materials.” This means, according to Miller, that, “you will be able to buy polyester fabrics that have easy-care elastic performance, and good wash and wear — not like spandex.” Products made with Cerenol can have  stretch recovery similar to that of spandex. But Miller noted that, when DuPont still had a PU fibres business, “anything that came along that had stretch ... the Lycra business objected... While Lycra was a DuPont business we were not allowed to develop it,” Miller said.

Now, “Within the next couple of years we will see some exciting new [fibre] products coming out,” said Miller.

For fibres, colour uniformity is paramount.

“Nobody wants a streak in their fabric.” Colour uniformity comes from, “having consistent quality ingredients — absolutely unvarying polymer quality, because then you can spin it into the same fibre and it dyes the same,” day-in, day-out, year-in, yearout, Miller added.

Asked about the very competitive nature of the spandex fibres market, with many Asian producers, and issues with overcapacity, Miller said that this is true. But that is, “because everybody has the same technology,” and the market is ready for something new, he said.

Sunkara pointed out that the fibres sector is interested in Cerenol because spandex uses solvent-based spinning systems, which need a lot of capital. With Cerenol, they could use existing assets for polyester or nylon spinning, “so people don’t have to spent a lot of money but still get a great product,” said Sunkara.

DuPont will not make the fibre, it will license the technology to make it.

Value for money ...

 Discussing pricing policy for Cerenol, Miller said, “We are going to value price it.” That means “you have to understand how useful it is and its value for your customers and their products, and price it in a fair way,” he said.

Any new product starts on a small scale, where costs are higher: “You try to position your product at the value end of the market initially. As the volume grows, you supply to larger parts of the market at prices they are willing to pay,” he continued.

Over time Cerenol “will be competitive with the best polyols out there in the market,” but is not likely to be as cheap as PPG, he added. But since it has “much better properties [and] makes a better polymer,” — it doesn’t have to be cheap, the DuPont executive noted.

Discussing the US Bio-Preferred programme, Miller said that, long term such a programme is not the way to operate the market. But for a small business, trying to get into the market, it offers “a leg up,” he noted.

He feels that such programmes should operate for a limited time to encourage development to be renewable and sustainable.

“Ultimately they have to be competitive without price subsidies,” he concluded.

EASY PROCESSING, HIGH TENSILE STRENGTH, HIGH ELONGATION

 Cerenol homopolyols are ether-linked long-chain molecules with an odd number of carbon atoms in the repeat unit. They have primary reactive hydroxyl end groups and are from a 100- percent renewable source.

As shown in Table 1, Cerenol polyols are low in viscosity: they are liquids at room temperature under dry conditions, but can solidify when exposed to low temperatures and a humid environment.

Table1: Properties of Cerenol polymers
Cerenol Polyol Type		H650	H1000	H1400	H2000
Renewable content	%	100	100	100	100
Hydroxyl number		160.9	113	78.7	55.9
Mn		698	993	1426	2006
Polydispersity, Mw/Mn		1.544	1.568	1.681	1.753
Unsaturation	meq/g	0.01	0.013	0.016	0.15
Viscosity @ 40°C	cPs	146	230	422	838
Colour	APHA	24	24	15	31
Alkalinity	meq/30 kg	0.44	0.9	0.9	1.9
1,3-propanediol	wt %	0.19	0.09	0.07	0.05

The Cerenol polyols from DuPont in Table 1 were used to make renewably sourced cast PU (RSCPU) elastomers and the properties compared with elastomers made from PolyTHF P650, P1000, and P2000 from BASF. Making prepolymers with Cerenol is easy, with good processing characteristics. Because they are liquid at or near room temperature and mix well with TDI (toluene diisocyanate) and MDI (methylene diphenyl diisocyanate), low reactor initiation temperatures are possible. This helps keep reaction temperatures low enough to avoid isocyanate side reactions, which will reduce prepolymer properties. Reactivity of Cerenol with isocyanates was excellent and comparable to the reactivity of PTMEG.. Compared to MDI-based prepolymers, the viscosity of TDI-based prepolymers was significantly lower (10 200 vs 53 000 cPs), so they are more easily processed. Prepolymer viscosities were substantially higher when PTMEG with low and high molecular weights was used. The low viscosity of Cerenol-based prepolymers is attributed to lower viscosity, narrower molecular weight distribution and lower intermolecular forces. In addition to easy processability, Cerenol polyols could be used to make new polyurethane elastomers with lower hardnesses which are otherwise not possible from PTMEG due to high viscosities. Tables 2 and 3 compare the properties of RSCPUs with those of materials made from PTMEG polyols. Overall, the Cerenol-based elastomers had excellent physical properties compared to the PTMEG ones. The Cerenol materials often combine high tensile strength with unusually high elongation, in the same elastomer. The implication is that these elastomers are likely to exhibit a high degree of puncture resistance and toughness in demanding applications.

Table 3: RSCPU (MDI) compared to non-RSCPU
Polyol		H650	P650	H2000	P2000	H2000	P2000
NCO,	%	8.16	7.95	5.1	5.09	3.31	3.19
Soft segment	%	51	51	72	72	78	78
Pot life	min	10	11	15	20	11.5	9
Demould time	min	90	60+	60	90	60	90
Hardness		91A	93A	77A	81A	67A	71A
100% Modulus	psi	2020	2271	741	846	417	539
300% Modulus	psi	3197	4102	1246	1607	767	1078
500% Modulus	psi	1920	3518	1383
Tensile strength	psi	5081	5864	4715	4736	2600	2324
Elongation,	%	576	450	850	560	675	450
Split tear (D1939)	pli	253	358	125	77	55	38
Die C tear	pli	577	568	323	282	165	142
Ball rebound	%	41	41	76	79	75	80
Compression set	%	31	27	25	15	34	16
Taber abrasion loss	mg	40	58	19	16	11	23

Two notable examples were the elastomer with 77A durometer (Table 3) with elongation of 850% and tensile strength of 4715 psi, and the 68D durometer (Table 2) elastomer with elongation of 300% and tensile strength of 7572 psi. Both materials would show high energy absorption before failure.

Table 2: RSCPUs (TDI/MOCA) compared with non-RSCPUs
Polyol		H1000	P1000	H2000	P2000
NCO,	%	6.18	5.97	3.58	3.47
Soft segment	%	62.5	63.4	76.9	77
Pot life	min	6	6.5	13.5	16
Demould time	min	30	30	75	120
Hardness		94A	94A	87A	88A

RSCPUs had higher tear strengths than PTMEG-based elastomers, except for that based on H650. Abrasion resistance of TDI-Cerenol based elastomers was comparable to that of PTMEGbased elastomers. But abrasion resistance of MDIbased RSCPUs was excellent, and superior to that of PTMEG-based materials, because these materials are softer and tougher. Compression set of the Cerenol elastomers was in general higher than that of the PTMEG comparisons, although a higher cure temperature of 110°C reduced compression set, albeit with some reduction in hardness and other physical properties. • Extracted from the paper given by Hari Sunkara  and Charles Demarest of Aragon Elastomers at the CPI event. DUPONT AND BIO-MATERIALS  Back in the 1940s, DuPont discovered some “very interesting properties of polymers made from PDO,” but had no commercial route to make it. Later, “we discovered we could make it [PDO] biologically from a fermentation process,” and with its fibre history, was able to launch Sorona PTT (polytrimethylene terephthalate) fibres. “You have to have reasonable cost and high purity to make fibres from it,” Miller pointed out. “Making sure we had the right PDO” to make polymers was “a critical step,” he commented. Sorona is a nylon-like material — being developed in a company that was at the time the world’s largest nylon producer, Miller emphasised. And Miller wryly noted that, had Shell not tried so hard to break into the nylon business with its Corterra PTT fibre, “we would not have been so motivated to develop our own product.” But Shell faltered with its PTT route. And DuPont found it had, ”a lot more PDO capacity than we needed.” That’s when Sunkara developed the condensation route for Cerenol. At that time, DuPont still made PTMEG, and had its Lycra spandex fibres business. “We started to discover very interesting properties,” said Miller. But internal tension arose: “Is this new product going to affect our existing product?” the PTMEG people asked. “Do we want it to be successful or do we want it to go away?” Miller’s view is that, “Products get old, they have a lifecycle. I always tell people ... if you are not willing to innovate, and replace yourself ... somebody else will.” When Sorona became successful, that also started to affect the nylon business. But DuPont then sold the Invista unit of spandex, nylon fibres and PTMEG business to Koch Industries. Sorona was able to stay in DuPont and compete with nylon, said Miller. But bio-technology was not the push behind Sorona: “We were running out of nylon capacity,” and to expand it would have taken a lot of capital. With Sorona, “we were able to do it much more cheaply.” As it turned out, “when we commercialised the bio route, the market was starting to recognise the value of sustainability of green feedstocks — and we had the goods,” noted Miller.