Polyterpene tackifiers

The other class of acrylic compatible tackifiers includes those based on ter-penes. Terpenes are monomers obtained by wood extraction or directly from pine tree sap. To make the polyterpene tackifiers, the monomers have to be polymerized under cationic conditions, typically with Lewis acid catalysis. To adjust properties such as solubility parameter and softening point, other materials such as styrene, phenol, limonene (derived from citrus peels), and others may be copolymerized with the terpenes. 

Common rosin and polyterpene tackifiers typically are fairly low in molecular weight (commonly in the neighborhood of 1000-2000 Da) and they have softening points in the range of 60-120°C. 

Barrueso-Martinez M.L., Ferrandiz-Gomez T.D., Romero-Sanchez M.D., Martin-Martinez J.M., Characterization of EVA-based adhesives containing different amounts of rosin ester or polyterpene tackifier, J. Adhesion, 79(8-9), 2003, 805-824. 

Polyterpene tackifiers are used as a less expensive resin to impart tack to a compound. 

Polyterpene tackifiers are used extensively in the adhesives industry. They are used in hot melt pressure-sensitive adhesives. 

Heteroatom functionalized terpene resins are also utilized in hot melt adhesive and ink appHcations. Diels-Alder reaction of terpenic dienes or trienes with acrylates, methacrylates, or other a, P-unsaturated esters of polyhydric alcohols has been shown to yield resins with superior pressure sensitive adhesive properties relative to petroleum and unmodified polyterpene resins (107). Limonene—phenol resins, produced by the BF etherate-catalyzed condensation of 1.4—2.0 moles of limonene with 1.0 mole of phenol have been shown to impart improved tack, elongation, and tensile strength to ethylene—vinyl acetate and ethylene—methyl acrylate-based hot melt adhesive systems (108). Terpene polyol ethers have been shown to be particularly effective tackifiers in pressure sensitive adhesive appHcations (109). 

Natural rubber displays the phenomenon known as natural tack. When two clean surfaces of masticated rubber (rubber whose molecular weight has been reduced by mechanical shearing) are brought into contact the two surfaces become strongly attached to each other. This is a consequence of interpenetration of molecular ends followed by crystallisation. Amorphous rubbers such as SBR do not exhibit such tack and it is necessary to add tackifiers such as rosin derivatives and polyterpenes. Several other miscellaneous materials such as factice, pine tar, coumarone-indene resins (see Chapter 17) and bitumens (see Chapter 30) are also used as processing aids. 

In this section the rosins and rosin derivative resins, coumarone-indene and hydrocarbon resins, polyterpene resins and phenolic resins will be considered. The manufacture and structural characteristics of natural and synthetic resins will be first considered. In a second part of this section, the characterization and main properties of the resins will be described. Finally, the tackifier function of resins in rubbers will be considered. 

Tackifiers. Resins are generally added to adjust the desired tack. In general, resins must be used with plasticizers to obtain a good balance between tack and cohesive strength. Typical tackifiers are polyterpenes, although hydrocarbon resins and modified rosins and rosin esters can also be used. In some cases, terpene-phenolics or phenol-formaldehyde resins are added to increase adhesion. 

Tackifiers. The tackifiers usually are hydrocarbon resins (aliphatic C5, aromatic C9) or natural resins (polyterpenes, rosin and rosin derivates, tall oil rosin ester). They improve hot tack, wetting characteristics and open time and enhance adhesion. The content on tackifiers in a hot melt can be in the region of 10-25%. 

Hydrocarbon resins comprise a range of low-molecular-weight products (M < 3000) used as adhesives, hot-melt coatings, tackifying agents, inks, and additives in rubber. These include products based on monomers derived from petroleum as well as plant sources. The petroleum-derived products include polymers produced from various alkenes, isoprene, piperylene, styrene, a-methylstyrene, vinyltuolene, and dicyclopentadiene. The plant-derived products include polyterpenes obtained by the polymerization of dipentene, limonene,... 

A tackifier is hard low-molecular weight resin with a Tg higher than room temperature. It can give the highest tack to the adhesive when added at the proper amount. Petroleum resin, polyterpene, and rosin esters are typical tackifiers, which are all commercially available. 

Nevtac . [Neville] Synthetic polyterpene resins tackifier for adhesives, coatings, rubber prods., concrete-curing conqxls., and caulking conq>ds. 

Tackifiers can be used to improve the tack properties of thermoplastic polymers, the compatibility between the polymer and substrate, wetting power, or the strength of the permanent bond. Tack is the bond strength that is formed immediately when a given material comes in contact with another surface, or instantaneous adhesion. Types of tackifiers include natural resins, phenolic resins, and polyterpenes. 

Figure 4 matches the tack strength performance of palm kernel oil alkyd resins as a tackifier in rabber compound againsta reference (the same ENR compound without alkyd), polyterpene (a 3-pinene resin with softening point of around 30°C) and petroleum resin (C5 type aliphatic hydrocarbon resin withsoftening point around 100°C), two of the very common tackifiers in the tire industry. These... 

Tackifier Reference Polyterpene Petroleum resin AlkFAlS AlkFA25 AlkFA35... 

The palm oil-based alkyds could be used as tackifiers to replace polyterpene and petroleum resin in ENR mbber compound. They could provide better tack strength, impart better road gripping and reduce rolling resistance in tread rabbet However, they should be apphed at low level to avoid reducing the abrasive resistance of the rabbet... 

As the PSA industry evolved, natural rubber (NR) and styrene-butadiene rubber (SBR) were the primary elastomers used. Other backbone polymers were available but were used to a lesser degree. These other elastomers include polychloroprene, butyl rubber and nitrile rubber. Traditionally, formulations containing natural rubber have made use of polyterpene resins as tackifiers, particularly beta-pinene resins. The probable structure of a beta-pinene resin is given as follows and represents the terpene class of resins. 

Fig. 5. Polyken Tack of Natural Rubber Latex Tackified with an Aromatic Modified Polyterpene Resin Emulsion...

The general classifications of resins which are recommended for use as tackifiers for natural rubber latex are polyterpene resins, modified polyterpene resins, modified aromatic hydrocarbons, and all rosin ester dispersions. 

Polyterpene resins are transparent, light yellow, odorless, nontoxic, brittle, solid thermoplastic polymers (softening point 80-125 °C) with a relatively low Mw in the range of 1.200-1.300. They are used as tackifiers in hot-melt adhesives for packaging, wood, furniture, and assembly adhesives, in bookbinding, hygiene, nonwoven fabrics, pressure sensitive tapes and labels, industrial and automotive adhesives, and aerospace... 

---