New VISIOMER® Terra IPGMA for low odor, high-performance methacrylate structural adhesives

Adhesives have become increasingly important for lightweight design and joining dissimilar materials. Structural adhesives permanently join critical components and replace less effective bonding methods such as welding and mechanical fasteners. They provide stiffness, strength, and durability. Methacrylate adhesives in particular are valued for their rapid cure and proven durability, making them indispensable in automotive, transportation, industrial, composite, and electronics applications. They are usually polymer-toughened systems that form strong bonds to a wide array of metal and polymer substrates while requiring only minimal surface preparation. Methacrylate adhesives provide high shear, peel, & impact strength while resisting chemicals and corrosion.

Odor is consistently ranked among the most important characteristics of methacrylate adhesives. The strong odor and flammability of adhesives based on methyl methacrylate restricts their use and may necessitate expensive ventilation systems.

To address these challenges, formulators developed low-odor adhesives containing tetrahydrofurfuryl methacrylate (VISIOMER® THFMA) and phenoxyethyl methacrylate (PhEMA). These alternatives reduce odor and provide adhesion but are classified as CMR substances, posing health risks during application.  With end-users demanding safer alternatives, a series of label-friendly and low-odor methacrylates were evaluated as replacements for tetrahydrofurfuryl methacrylate and methyl methacrylate. Among these, VISIOMER® Terra IPGMA, isopropylidene glycerol methacrylate, exhibited outstanding performance.

Label-friendly and low-odor methacrylates were examined in a model 2k, polymer-toughened structural adhesive as alternatives to MMA and VISIOMER® THFMA. More than any other monomer tested, VISIOMER® Terra IPGMA was found to significantly improve adhesion without losing elasticity. In general, lap shear adhesion can be increased using high T_g, hard monomers to increase the modulus. Materials with higher E-modulus (Young’s modulus) are stiffer and resist deformation more effectively, distributing stress more uniformly throughout the adhesive layer.  This results in higher bond strengths in a lap shear test. Since modulus is inversely related to impact resistance, adhesives with too high modulus are less able to absorb energy and more prone to fracture or damage. Compared to other low-odor monomers, VISIOMER® Terra IPGMA has the highest ratio of lap shear to E-modulus of any monomer tested - more than 25 percent higher than the current industry standard. This indicates that VISIOMER® Terra IPGMA offers superior adhesion while preserving flexibility, making it suitable for demanding applications where impact resistance is essential. 

When substituting methyl methacrylate, many low-odor methacrylates can initially reduce mechanical strength due to lower glass transition temperatures (Tg). Careful combinations of low-odor methacrylates, like VISIOMER® Terra IPGMA, with high Tg methacrylates, such as VISIOMER® Terra IBOMA isobornyl methacrylate (72 percent bio-content) or VISIOMER® TMCHMA trimethyl cyclohexyl methacrylate, can help surpass the performance of and reduce hazards associated with traditional formulations that rely on MMA, VISIOMER® THFMA, or PhEMA.

Our tests also demonstrated that VISIOMER® Terra IPGMA is nearly odorless. An odor panel comprised of more than twenty test subjects revealed that the minimal odor of VISIOMER® Terra IPGMA is much more favorable than any other low-VOC methacrylate or MMA, including GLYFOMA glycerol formal methacrylate, PhEMA, and VISIOMER® THFMA. All low-odor methacrylates have vapor pressures significantly lower than the vapor pressure of MMA.

Evonik’s VISIOMER® Specialty Methacrylate portfolio includes other tools to help formulators balance the properties of low-odor adhesives. VISIOMER® Terra IBOMA and VISIOMER® TMCHMA may be selected for their dimensional stability and high heat resistance. Low volatility, low odor diluents like VISIOMER® BNMA are effective diluents while VISIOMER® Terra IPGMA additionally increases adhesion.  VISIOMER® HEMA-P methacryloyloxyethyl phosphate functional methacrylate improves corrosion resistance and increased substrate adhesion up to 300 percent on some metals. Please contact your Evonik VISIOMER® Specialty Methacrylates representative who can help you select the best candidates for your formula. 

The market for methacrylate structural adhesives continues to grow as applications of lightweight, fast, and efficient construction methods expand. Manufacturers expect high performance, rapid-cure adhesives which are even safer & easier to handle, and the list of substrates requiring strong bonds keeps growing as new materials are introduced.  Further challenges including sustainability are already shaping the next generation of adhesives. Alone or in combination, VISIOMER® low-odor monomers help formulators adapt to new requirements while maintaining high performance in these critical adhesives.