by 2017 Abstracts No Comments

Pressure-sensitive adhesion is not a typical property of polyurethanes and has been imparted by adding tackifiers or by compounding to adjust their glass transition temperature and decrease their elastic modulus at room temperature. Several patents on PU PSAs have been filed in the 70s and 80s, and more recently the use of waterborne polyurethane dispersions for preparing PU PSAs has been proposed. However, the structure-properties in PU PSAs have not been sufficiently addressed. Typically, the polyurethanes intended for PSAs (PU PSAs) are synthesized by using low NCO/OH ratios and polyols of high functionality. However, insufficient crosslinking is generally produced and the performance of the polyurethane PSAs is limited. In this study several new thermoplastic polyurethanes were synthetized for developing PSAs with controlled properties, tack mainly, based on the design of their structure.

Thermoplastic PU PSAs were prepared using the prepolymer method. Different NCO/OH ratios were selected and the raw materials used were MDI isocyanate, 1,4-butanediol chain extender, and several polyols of different molecular weights – polypropylene glycols (PPG1000, PPG2000), tetrahydrofurane polyols (PTMEG1000, PTMEG2000), polyadipate of 1,4-butanediol (PE).

The increase of the amount of PPG2000 up to 50wt% in the mixture of polypropylene glycols increases the tack of PU PSAs, and the higher content of PPG2000 does not affect significantly the tack or the 180º peel strength of the PU PSAs. On the other hand, the use of mixtures of PPG and PTMEG produces PU PSAs with smaller 180º peel strength but high tack at 25 ºC. The increase of the NCO/OH ratio does not affect tack or the 180º peel strength, although the cohesion is increased. The viscoelastic window for PU-PSA formulations with NCO/OH ratio near 1.10 corresponds to general purpose PSA, and the increase of the NCO/OH ratio displaces the viscoelastic window toward higher shear PSA. The glass transition temperatures of PU-PSAs range between -47 and -42 ºC, a value adequate for PSAs at room temperature. Finally, the tack of PU PSAs prepared with mixtures of PPG and PE can be varied noticeably by designing its composition, i.e. an increase or a decrease in tack with temperature can be obtained.

 

Co-author:

Mónica Fuensanta-Soriano, Adhesion and Adhesives Laboratory, University of Alicante, Alicante, Spain

FEICA Conference