Advancements in polymer productions continue to blur the lines between plastics and rubbers. I hope to spend several blog posts to cover some of these unique materials. Today’s post will highlight PB-1. Currently LyondellBasell is the largest producer but Korea is also seeing increased volumes as technology continues to improve.
PB-1 or polybutene-1 (C4) resin is a semi-crystalline, highly isotactic thermoplastic, derived from polymerization of butene-1 utilizing Ziegler-Natta type catalyst. Characterized by high amorphous content and homogeneously dispersed crystalline regions, it’s high molecular weight chains (250,000~450,000) and bulky pendant groups give it qualities such as high creep resistance and unique crystallization and flow behavior. Its relatively slow kinetics of crystallization allow for an excellent wetting behavior. Its highly shear-sensitive flow behavior means that it remains easily dispersible also in even more incompatible polymers like thermoplastic elastomers.
Target applications include pipes, easy-open packaging (film), and adhesives. It is highly compatible with polypropylene but does not mix well with polyethylene. This is incompatibility is used to its advantage in applications like easy-open or easy-peel packaging.
PB-1 pipes are finding a place in the hot & cold plumbing, underfloor heating, and district heating markets. Advancements in flexibility, temperature resistance and creep resistance often give pipes made from PB-1 and advantage over traditional pipe materials such as PPR and PE80 or PE100. However, price continues to be a barrier for many regions.
PB-1 is less compatible in blends with polyethylene but it is still easily dispersible. Mentioned above, this incompatibility forms a 2-phase structure which is the basis of seal peel technology for easy-opening packaging applications. The dispersed regions of PB-1 within a polyethylene film create breaking points or cohesion failure when stress it applied to the film. Easy-open films created with PB-1 often have similar initiation and propagation forces making them ideal for easy peel applications. Some potential benefits in film production might include lower sealing temperatures, reduced crystallinity, and easy dispersion.
While less common than pipe and film, PB-1 is also finding uses in hot melt adhesives. Homopolymer grades of PB-1 offer high cohesive strength while copolymer grades slow crystallization which prolongs the “open time” of the adhesive.
PB-1 is also being used as an additive to polymers such as PP to compete with traditional TPEs. Depending on the application, PB-1 may improve flowability and scratch resistance. Low blush qualities are also possible as well as improved elasticity and tear resistance making PB-1 a very interesting member of a new generation of soft plastics. It will definitely be interesting to see how the adoption of PB-1 by producers compares to other materials such as ExxonMobil’s Vistamaxx, Dow’s Versify, and Kraton’s line of SEBS polymers.