A PARADIGM SHIFT FROM CONVENTIONAL BONDING CHEMISTRY TO ADHESIVE CHEMISTRY AND ITS EFFECTS ON PRODUCT PERFORMANCE PAPER PRESENTED AT JEC AMERICAS 2014 BY MARK DE SOUZA IMPROVEMENTS IN COMPOSITE MATRICES USING CLEANER RESIN ALTERNATIVES
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A PARADIGM SHIFT FROM CONVENTIONAL BONDING CHEMISTRY TO ADHESIVE CHEMISTRY AND ITS EFFECTS ON PRODUCT PERFORMANCE
PAPER PRESENTED AT JEC AMERICAS 2014 BY MARK DE SOUZA
IMPROVEMENTS IN COMPOSITE MATRICES USING CLEANER RESIN ALTERNATIVES
INTRODUCTION TO CLEANER RESIN SYSTEMS
At a time when health and environmental concerns are gettingincreasingly important, “cleaner” resins have become a priority andare currently being developed. Furthermore, the very versatilePolyurethane resins present many advantages over polyester andepoxy ones and are gradually being used more in a wider variety ofprocesses ranging from pultrusion, RTM, VARTM, Infusion, Pre-pregs,Spray-up to Filament Winding.
CURRENT COMPOSITE SCENARIO – EPOXY RESIN SYSTEMS
• Current Epoxy Resins use BPA (Bisphenol Epichlorohydrin, a key component of commercial EpoxyResin Systems)
• Bisphenol A (BPA) is a suspect endocrine disrupting chemical• BPA can leach from epoxy resins – possibly causing severe adverse human health effects (based on
more than 100 scientific papers)• Liver enzyme damage• Damage to brain and reproductive organs• Damage development of embryos• Linked to breast cancer• Low doses linked to increase risk of prostate cancer
• A 2005 bio-monitoring study detected BPA in 95% of U.S. Citizens• California bill introduced to ban BPA in certain toys and child care products• US-EPA conducting alternative search to BPA for its use in pipes and pipe linings• Additionally Epoxy Curatives like MDA are suspect carcinogens and require special handling and
disposal procedures• Future potential for worker exposure lawsuits. Precedent has been set with Asbestos.
CURRENT COMPOSITE SCENARIO – STYRENE ESTER BASED RESIN SYSTEMS
• Thermoset polyester extensively uses both styrene monomer & MEKP as volatile solvents– risk of fires in process and storage areas
• Styrene monomer has been (in some studies) shown to be a carcinogen, and is currentlyclassified as a suspected carcinogen. It can cause CNS issues & lead to fatal cardiacsensitization (IARC). Styrene is classified as a hazardous air pollutant, and emissions arestrictly regulated as a VOC
• Enzymes have been found in human lungs that convert styrene into styrene oxide, whichthen develops tumors in lungs of mice
• MEKP is a severe skin irritant, requiring careful treatment as a hazardous waste. Must bedisposed of at a RCRA approved facility
• Styrene monomer may be regulated even tighter in the near future, resulting in lowerpermit levels, thereby limiting production and forcing several large industries to scramblefor alternatives (spa, tub, RV, boat, etc.)
CONVENTIONAL RESIN SYSTEMS – IMPACT AND HAZARDS
STYRENE ESTER SYSTEMS (Polyester, Vinyl ester)• Styrene emission limitations affect plant output• Styrene permits unavailable in certain areas, limiting growth• Future potential for worker exposure lawsuits• Expensive ventilation and incineration equipment• Hazardous waste handling adds expense• Yield losses are high, due to styrene losses• Potential fire issues due to flammability of styrene and MEKPEPOXY RESIN SYSTEMS (BPA)• Future class action suits against companies whose products could possibly leach BPA
into the human body• Human health effects have been documented in over 100 scientific papers and
government studies– Increased risk of breast cancer– Increased risk of prostate cancer– Increased risk of brain, liver, reproductive organ damage– Increased risk of miscarriages among women exposed to BPA
POLYURETHANE THERMOSET RESIN SYSTEMS FOR FIBER REINFORCED COMPOSITES
In view of the growing concerns on the use of BPA in the Industry and the actions initiated Environment Protection Agencies worldwide, a cleaner environmentally preferable alternative has been proactively developed for Cleaner Composites.
The resin system : A two part POLYURETHANE Thermoset resin with no Volatile Organic Compounds (VOC) and harmful chemicals like BPA.
Advantages of the new resin system:– No harmful leachates, or VOC.– Higher mechanical strength to – Higher thermal properties, – Better chemical resistance– Better UV and weathering resistance– Lower cost per pound of resin mix when compared to Epoxy and Vinyl Ester.
BETTER PERFORMING COMPOSITES THROUGH BETTER COMPOSITE MATRICES
• While the properties (mechanical & thermal) of Polyurethane resin systems can be ascertained by standard test methods, it is necessary to understand why polyurethanes can outperform incumbent resin system and yet be viable cost effective alternatives.
• Polyurethane resin systems are not dependent on the fiber reinforcements sizing chemistry to build a bond between the reinforcement fiber. As a result of this key difference, better composite matrices are formed.
THE EFFECT OF SIZING ON IMPROVED COMPOSITE MATRICES
• Most Commercial and Industrial Fiber reinforced plastics (FRP) utilize Polyester and Epoxybased resin systems to build composite products and structures utilized for a wide variety ofapplications ranging from water distribution, desalination & treatment, power generation,chemical process equipment, wind energy to automotive, residential & architecturalproducts
• A great composite structure is formed when each individual strand of the reinforcementmaterial is completely enveloped in the resin system. Without the cured resin holding eachreinforcement fiber in place within the composite matrix and thereby transferring the loadinto the composite matrix, premature and localized failures will be experienced.
• Reinforcement materials do not bond to the resin system directly and hence thereinforcement is surface coated with sizing chemistry so as to promote secondary bondingbetween the resin and the glass strand.
• This presents a plethora of problems• The sizing chemistry dictates the compatibility to the resin system• Stability of the sizing during glass coating process (foam, grit, pH, particle size) and its
effects on the composite• The sizing coating process variations can exponentially deteriorate the quality of
laminates (mechanical strength, dry fiber, streaks / white fiber )
REINFORCEMENT SIZING – CONVENTIONAL BONDING CHEMISTRY
Conventional Resins slip away from the surface of glass
without bonding
ABSENCE OF SIZING
Conventional Resins create secondary bonds to the glass coated with sizing through
chemical bonding
COMPLETE SIZING ENVELOPE
Conventional Resin Systems not enveloping the strand in areas where sizing is absent
INCOMPLETE SIZING ENVELOPE
Conventional resin systems like Polyester (Isophthalic, Vinyl ester resins) andEpoxy form bonds to the sizing chemistry which is in turn bonded to the glass.This is termed as a secondary bond.In locations where the sizing film is absent from the surface of the glass strand,there will not be a bond between the resin and the glass.
FIBER STRAND
RESIN
SIZING
SIZING ABSENT
ADHESIVE CHEMISTRY – A PARADIGM SHIFT
For decades, the fiber reinforced composite industry has been dependent on thereinforcement manufacturer to provide reinforcement products effectively andcompatibly sized to suit the resin system being utilized in the process of manufacture ofcomposites. This has resulted in product offerings like• Polyester compatible rovings (suitable for Polyesters and Vinyl ester resin systems)• Epoxy compatible rovings (suitable for Epoxy Resin systems)• Multi-compatible rovings (a trade-off with suitability adjusted for both polyesters, vinyl
esters and epoxies leading to a compromised chemistry)
Even if the reinforcement is sufficiently applied to the strands the same may bedamaged during packaging & handling as well as when the same is run through themanufacturing process (tension bars / rods / bath)
Sizing film former technologies are similar to those used in the paint industry and verylimited R&D effort or resources are being spent on improving the dated technology.
A NEW BREAKTHROUGH IS REQUIRED TO GET PAST THESE PROBLEMS TO ENSURE A BETTER COMPOSITE MATRIX
ADHESIVE CHEMISTRY – A BREAKTHROUGH FOR THE COMPOSITE INDUSTRY
Polyurethanes (Thermoset resin systems for composites) present a unique ‘out-of thebox’ solution to this problem
Thermoset Polyurethane Resin Systems can be formulated to bond equally well with thefiber reinforcement directly as with sizing coated glass and hence eliminating avariable of sizing inconsistencies.
In addition to eliminating the problems relating to sizing inconsistencies, a betterlaminate is produced without the incidence of dry fiber / streaks.
Polyurethanes provide equal of higher mechanical properties to Epoxies in terms oftensile & flexural strengths and can be formulated to have high Tg’s ranging from 80 -1800 C
ADHESIVE CHEMISTRY – A BREAKTHROUGH FOR THE COMPOSITE INDUSTRY
Due to improved fiber reinforcement adhesion (“Adhesive Chemistry”) there isa greater adhesive bond around each individual strand in polyurethanes resinsystems than in epoxy. Additionally there is an improvement in the bondingbetween strands an indication of better impregnation. The above pipes werefilament wound and it can be seen that the epoxy pipes have lesser amountsof resin between each individual strand.
Photomicrograph of an Epoxy Filament wound pipe at 50X magnification.
Photomicrograph of a Polyurethane Filament wound pipe at 50X magnification.
ADHESIVE CHEMISTRY – A BREAKTHROUGH FOR THE COMPOSITE INDUSTRY
Using the “Percent Area module” through ‘Scentis image ana lysis software’ to determine thevoid content values. Three photos at 50X were taken across both samp les. Each of thesephotos was evaluated with the software and the average is as follows.Epoxy - 1.66%Polyurethane - 0.60%The Percent Area module allows for adjustment of th resholds so that each area/phase/pore ismore accurately counted . Thresholds that prov ided the best combination of pores/v oids wereincluded.
Photomicrograph of an Epoxy Filament wound pipe at 50X magnification.
Photomicrograph of a Polyurethane Filament wound pipe at 50X magnification.
ADHESIVE CHEMISTRY – A BREAKTHROUGH FOR THE COMPOSITE INDUSTRY
Being an adhesive, Polyurethane tends to have a better bond to the glasssurface and appears to fill in the spaces between the strands better ascompared to conventional systems as seen in themicro-images.
Polyurethane Resin Systems enveloping the strand in areas
where sizing is absent
POLYURETHANE RESIN ENVELOPE
Conventional Resin Systems not enveloping the strand in areas where sizing is absent
CONVENTIONAL RESIN ENVELOPE
FIBER STRAND
RESIN SIZING
ADHESION TO GLASS WITHOUT SIZING - SIMULATION
IMPROVED MECHANICAL PROPERTIESHigher Tensile & Flexural Strength ! Higher Impact Resistance !
Higher Elongation !
Burst Tests on Filament wound products
Polyester Polyurethane
465 PSI 550 PSI
Epoxy Polyurethane
880PSI 1250PSI
40% Greater Mechanical strength
(Epoxy) and 20% for Polyester
TEST METHODSASTM D638
ASTM D790
ASTM D256
ASME SEC. X
THERMAL PROPERTIES – tg1 (GLASS TRANSITION TEMPERATURE)
While Post-cure improvesthe tg of Epoxy systems toabout 145C, there is littlechange in the tg ofPolyurethane resin systemsand hence post cure maybe avoided unless requiredfor post machining stressrelief
TEST METHODASTM D3418
EFFECTS OF UV
Epoxy & Polyurethane specimen exposed for 1 year in a UV / Humidity Chamber. While epoxy systems experience photo-degradation, polyurethane
systems are yellowed by exposure
TSE INDUSTRIES INC.
For more information contactMark D’Souza
Director – Research & Development (Composites)727-540-1306
Mark.DeSouza@TSE- Industries.com
5260 113th Avenue North, Clearwater, Florida 33760TEL: 1-800-237-7634 FAX 727-230-8090
www.TSE-Industries.com www.TSE-EcoWind.com
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