By Jan H. Schut
Three new families of bio-based thermoplastic elastomers, one based on starch, one on castor oil, and one on an undisclosed combination of commercial biopolymers, claim properties comparable to, or higher than, those of traditional styrenic TPEs. The emerging bio materials will be included by Teknor Apex Co. in Pawtucket, RI (www.teknorapex.com); Arkema SA in France (www.arkema.com); and GLS Thermoplastic Elastomers (www.glstpes.com) in McHenry, IL, in papers at the Society of Plastics Engineers upcoming 9th TPE Topical Conference (TopCon) Sept. 13-15 in Akron/Fairlawn, OH (www.akronspe.org, http://www.4spe.org).
Traditional styrenic-based TPEs are compounds of a polyolefin with a rubbery styrenic and mineral oil softening agent. Teknor replaces the polyolefin matrix with thermoplastic starch, blended in house under license. Arkema uses proprietary nylon 11 from castor oil. GLS (part of PolyOne) uses a “completely new” patent pending combination of bio polymers, which GLS won’t disclose because the patent application hasn’t published.
The three companies target different softness ranges. Teknor offers soft bio TPEs down to 30 Shore A, but with only 30% bio content. Arkema offers medium hard grades with up to 94% bio content. GLS offers soft grades with up to 79% bio content. All three produce bio TPEs in limited pre-commercial quantities for testing, but say they could ramp up. To reach high bio content for soft TPEs will require more than a bio-based matrix. It will take bio-based “soft” blocks and oil, which none of the players have identified so far.
TEKNOR’S HIGH BIO TERRALOY
Teknor’s paper [“Novel TPE Development Provides New Application Opportunities” by Elliott Pritikin, Sachin Sakhalkar, Bung-Lin Lee, and Kevin Cai] includes the company’s bio-content TPEs based on its Terraloy starch blending technology, exclusively licensed from Cerestech Inc. in Montreal (www.cerestech.ca). Cerestech is a spin off from the Ecole Polytechnic of Montreal, which developed the technology.
Teknor has commercialized five Terraloy MP grades already, all with 30% starch blended with petro-based polypropylene and polyethylene in a hardness range of 30-75 Shore A. These target consumer goods and hand-held devices. Teknor is now working with Cerestech to replace the elastomer and mineral oil with bio materials to create 100% bio TPEs.
PROPERTIES OF TERRALOY MP
Grade MP-2490H MP-2490G MP-2490F MP-2490E MP-2490D
Bio Content, % 30 30 30 30 30
Spec. Grav. 0.906 0.919 0.945 0.937 0.923
Sebum Oil Immer-
sion, wt % 9.3 12.5 2.3 9.7 1.4
Hardness, Shore A 30 55 60 67 75
Tens. Str., psi 382 437 752 571 806
Tens. Elong., % 761 741 756 694 619
@ 100%, psi 76 163 198 245 318
@ 300%, psi 145 232 299 332 454
Source: Teknor Apex
ARKEMA’S PEBAX RNEW
Arkema will present the latest developments in its Pebax Rnew TPEs [“Pebax Rnew: A Thermoplastic Elastomer Made From Renewable Resource for Low Temperature Applications” by Frederic Malet, Rene-Paul Eustache, Basker Lalgudi, and Eric Gamache]. First introduced in 2007, Rnew combines two of Arkema’s oldest chemistries: nylon 11 (Rilsan B) derived from castor oil, dating from 1947, and PEBA (polyether amide block copolymer) for soft TPEs, dating from 1981.
To make Pebax Rnew Arkema substitutes bio nylon 11 for petro nylon 12 in the Peba. Nylon 11 crystallizes faster than nylon 12 and gives different properties. Having an odd number of carbons (11 instead of 12), nylon 11 crystallizes into parallel chains with a combination of hexagonal and triciclic crystalline morphology. Nylon 12 crystallizes into coarse spherulites with only monoclinic crystalline morphology. Under heat or stress, nylon 11 transitions from triclinic crystalline morphology into a pseudo hexagonal crystalline structure, which gives nylon 11 more impact strength, higher melt temperature, higher elasticity, and better strain hardening than nylon 12.
Pebax Rnew won an environmental prize at the SPE’s GPEC 2010 conference last March. It’s available in seven grades with bio contents of 26 to 95 percent and medium-to-hard Shore D levels from 35 to 71. The soft domains are still petroleum based.
PROPERTIES OF PEBAX RNEW
Grade 25R53 35R53 40R53 55R53 53R53 70R53 72R53
SA 01 SA 01 SA 01 SA 01 SA 01 SA 01 SA 01
Bio content, % 26 30 46 64 79 89 95
Shore D 35 32 42 53 61 70 71
Melting point, F 135 146 148 167 168 186 186
Flexural mod., 10 40 75 160 245 360 560
GLS’S VERSAFLEX BIO
GLS recently added over-molding functionality to its emerging Versaflex BIO TPEs [“Bio-Renewable Thermoplastic Elastomers” by Guoqiang Qian, Krishna Venkataswamy, and Charles Page], which weren’t suitable for over-molding when they were introduced at NPE 2009 in Chicago last year. Now formulations can be molded over ABS and polycarbonate.
GLS offers seven Versaflex BIO TPE alloys, ranging from 22 Shore A, the softest bio TPE on the market, to 88 Shore A. The 22 Shore A elastomer also has high bio content of 64%. GLS has filed two patent applications on the new TPEs, which can be injection molded, extruded, and blow molded. They target consumer products like razors, hand-held devices, consumer electronics and medical applications, where over molding is important. Previously GLS commercialized four grades of Onflex BIO TPEs with lower bio content of 20-30%. Onflex is based on Pearlthane ECO, a bio TPU from Merquinsa in Spain (www.merquinsa.com), which has 30-50% bio content from vegetable-based polyols.
PROPERTIES OF VERSAFLEX BIO
Grade LC Versaflex Versaflex Versaflex Versaflex LC LC
343-060 BIO BIO BIO BIO 359-079B 359-079C
5550-40 5550-50 5550-60 5550-70
Shore A 22 42 52 62 68 81 88
(%) 64 70 68 65 66 78 79
Spec. Grav. 0.99 1.0 1.0 1.0 1.0 1.0 1.01
(MPa) 1.57 2.71 4.18 5.76 7.34 10.78 11.78
(MPa) 0.66 1.54 2.12 2.90 3.42 6.81 7.94
Break (%) 300 240 300 315 450 200 215
(kN/m) 2.41 13.6 19.1 29.1 47.1 48.9 62.7
Set (%, 22h
@22dC) — 17 20 20 21 34 31
OTHER POTENTIAL SOFT BIO INGREDIENTS
There aren’t many commercially available bio monomers to choose from. Du Pont Co. (www.dupont.com) makes Hytrel RS, a thermoplastic polyester elastomer based on its Cerenol bio polymer, made from propanediol from corn sugar. It was developed with Genencor International in Palo Alto, CA (www.genencor.com), a unit of Danisco in Denmark. Hytrel contains 20-60% bio polymer in the hardness range of 30-83 Shore D. Merquinsa also makes Pearlbond ECO TPU with up to 90% bio content. Pearlthane ECO and Pearlbond ECO grades range in hardness from 80 Shore A to 60 Shore D. Theoretically, natural rubber could also be used as soft domains, but this would be complex because rubber requires fine dispersion with compatibilizers, plus catalysts and cross-linking agents.
New soft bio monomers are also on the way. Genencor developed the first bio isoprene in partnership with Goodyear Tire & Rubber, which Goodyear announced this year in Denmark. Bio isoprene is made by a fermentation process based on sugar, but won’t be commercially available until after 2015. Gevo Inc. (www.gevo.com) in Englewood, Colo., is developing bio isobutene based on corn sugar to make bio butyl rubber. Gevo works with Lanxess Inc. in Sarnia, Ont., a large producer of synthetic rubber and also an investor in Gevo.