When faced with improving the performance of polyurethane articles with respect to toughness, abrasion and cut-chip resistance; a broad thermal profile (low and high-temperature performance) and durability; chemical, oil, and solvent resistance; hydrolysis resistance; and processing, formulators turn to Gantrade’s variety of polycaprolactone polyol grades to maximize a broad cross-section of these parameters.
The wide variety of polycaprolactone polyol structures available enhances the capabilities of formulators looking to design polyurethane elastomers that meet specific demanding performance attributes and service life.
Caprolactone polyols are available at Gantrade in molecular weight grades from 310 to 4000, and we offer these polyols as diols, triols, and tetraols. They are created through a facile ring-opening polymerization (ROP) process under mild conditions using an initiator diol or triol along with a caprolactone monomer. The ROP process is depicted in the graphic below.
There are over 30 grades of Placcel polycaprolactone polyols available at Gantrade. Our company is a global leader in the supply of polycaprolactone polyols for an array of industry applications. Let’s take a quick look at five key facts about our family of polycaprolactone polyols.
1. Polycaprolactone polyols provide a key number of performance advantages over conventional polyester polyols in PURs.
When compared with adipate-based polyester polyols in polyurethane elastomers, caprolactone polyols demonstrate the following performance advantages:
- Better low temperature flexibility and high temperature performance
- Flex-fatigue life, elastic memory, impact resistance, and toughness
- Cut, chip, and tear strength
- Enhanced abrasion resistance
- Superior resistance to hydrolysis
- Higher chemical resistance to oils, fuels, and solvents
- Greater weatherability and UV stability
- Processing advantages due to their low viscosities and low polydispersity
Formulators can further enhance these general property sets through the proper selection of the polycaprolactone polyol used to produce polyurethanes requiring demanding performance attributes and service life.
2. The primary PUR applications for polycaprolactone polyols cover a broad spectrum of the elastomers industry.
The superior dynamic properties of the polycaprolactone based elastomers are especially useful in polyurethane high-speed wheels and roller applications to name a few. The inherent oil and chemical resistance, hydrolysis resistance, and toughness of these polycaprolactones are useful in TPUs for the oil, mining, and automotive industries, as well as conveyor belts, hydraulic and pneumatic seals, and gaskets. The greater transparency is beneficial in transparent interlayer film, paint protective film (PPF), safety glazing, and sheet and surface protection film applications where excellent durability, abrasion and scratch resistance, oil and solvent resistance, and UV resistance are required. Other applications include adhesives, industrial coatings, textile and leather coatings, footwear, hoses, tubes and profiles and belting.
3. The initiator comonomer is a major differentiator of polycaprolactones in PUR elastomers.
Take a look at the list below, as we outline just some of the initiator comonomers (R-[-OH]f] that are used in building polycaprolactone polyols, as well as the key characteristics in the resulting polyurethane elastomer.
- Ethylene Glycol: General purpose initiator affording a good balance of properties. Special features are available with narrow MW grades.
- Diethylene Glycol: Contributes some polyether performance characteristics and liquid diols. Lower propensity to cold crystallize in a PUR.
- Neopentyl Glycol: Reduced propensity to crystallize and better hydrolytic stability.
- Butanediol: High cut, tear, and chunk resistance, as well as high-tensile properties.
- Hexanediol: High-tensile and thermal properties, as well as cut-chip resistance.
- PTMEG Polyol: Enhanced hydrolytic stability, low-temperature properties, and low crystallization tendencies.
- Trimethylolpropane: Trifunctionality for enhanced performance attributed to light crosslinking.
The molecular features of the various initiator comonomers express themselves in polyurethane characteristics like crystallization tendencies, dynamic properties, strength, and durability. Some initiators like NPG and DEG enable liquid polyols at lower molecular weights. The triblock diol with PTMEG initiator, as well as the NPG and DEG initiators, afford PUR soft blocks with a low propensity to crystallize and cold harden in a PUR elastomer.
4. The low acid values associated with polycaprolactone polyols imparts significant benefits.
A key feature of polycaprolactone polyols are their very low acid values, since their synthesis does not involve an acid intermediate. Because any residual acid catalyzes ester hydrolysis, low acidity, and the inherent hydrophobic nature of these polyols, polycaprolactone polyols afford polyurethanes with greater moisture resistance.
An example of this dynamic are the low acid values of Placcel 220 T with an acid value of 0.01 KOHmg/g versus values above 0.50 KOHmg/g for conventional adipate-based polyester polyols. Theimprovement in hydrolysis resistance for the Placcel T series manifests itself in very good tensile strength retention values for Placcel 220NT when compared with Placcel 220N, PTMEG 2000 (a hydrophilic diol), and a 2000 MW HDO adipate in a wet environment at 80°C. A polycarbonate diol (PCD) reference is provided since PCDs are known to exhibit the highest retention of wet properties in a polyurethane formulation.
The low acid values result in higher hydroxyl end-group reactivities with isocyanates, since acidity often reduces the activity of catalysts that may be incorporated. Daicel has developed low acidity Placcel grades that exhibit lower reactivity with isocyanates, without compromising the benefits of low acidity.
5. Polyol molecular weight and molecular weight distribution (MWD) dramatically influence PUR elastomer properties.
The polyurethane soft-segment mainly affects the elastomeric and dynamic properties and low-temperature performance, while the hard urethane segment influences the hardness, tear, cut, and chip resistance. The degree of phase separation of the two segments in a polyurethane increases with the polyol molecular weight. This phenomenon results in a reduction of the Tg for higher molecular weight polyols (MWs) and enhanced elastomeric characteristics. For the caprolactone polyols, crystallinity and cold hardening increase at higher MWs.
The other key molecular weight variable is the degrees of polydispersity (MWD). A significant reduction in polydispersity has been achieved with the Placcel N series of diols, resulting in superior dynamic properties, excellent elastic recovery and resiliency properties, high transparency and light transmission, and other attributes.
The manifestations of diol molecular weight and narrow polydispersity can be observed in the table to the right, which compares the properties for three different MW grades of polycaprolactone polyols in a TPU at equivalent hardness values. The lower molecular weight polyols show superior transparency, high tear strength, and high elastic recovery. The higher MW polyols exhibit better low-temperature performance, higher elongations, and reduced compression set values.
BASIC PROPERTIES OF TPUS BASED ON MW GRADES
|HS CONTENT (%)||42.1||35.5||32.3|
|TPU HARDNESS (A)||84||83||84||ISO 7619|
LIGHT TRANSMITTANCE (AT 400NM, %)
|TENSILE STRENGTH (MPA)||39.5||37.5||40.9||ISO 37|
|ELONGATION (5)||371||490||458||ISO 37|
|TEAR STRENGTH||91.3||88.4||85.1||ISO 34|
|COMPRESSION SET (70C X 24HR, %)||33.2||16.1||17.7||ISO 815-1|
|ELASTIC RECOVERY (%)||78.9||78.3||18.3||*|
*SAMPLES WERE STRETCHED TO 300% ELONGATION AT DEFORMATION RATE OF 500 MM/MIN. AFTER KEEPING FOR 10 MINUTES, THE STRESS WAS RELEASED AT THE SAME RATE. WHEN X IS DISTANCE BETWEEN TWO MARKED LINES, X’ IS DISTANCE BETWEEN THE MARKET LINES MEASURED 10 MIN AFTER. ELASTIC RECOVERY (%) = [1-(X’-X)/X]*100%
Learn more about polycaprolactone polyols from the experts at Gantrade.
Known worldwide as a leading distributor of polyols used in a variety of market applications, Gantrade is the supplier of choice for manufacturers in industries ranging from paint and coatings to sealants and adhesives, performance elastomer, construction, packaging, and more. Look to our team of experts for up-to-date market information and technical support for matching our polycaprolactone polyol products from Placcel to your unique product specifications. Contact us today to get started.