China
Africa
Explore chapters and articles related to this topic
Additive Manufacturing and Its Polymeric Feedstocks
Published in Antonio Paesano, Handbook of Sustainable Polymers for Additive Manufacturing, 2022
The feedstock materials for VP must contain, as mentioned earlier:A reactive, UV-curable monomer or oligomer or a blend of them that crosslink and polymerize into a solid object.A photoinitiator or a blend of them that is degraded when exposed to the light source, and forms radicals, cations, or carbene-like species that activate the process of polymerization (Bartolo 2011). Bagheri and Jin (2019) published a comprehensive and detailed list of photoinitiators with names, chemical structure, wavelength, and references, including among others:For UV light: benzophenone, diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxideFor visible light: camphorquinone, bis(4-methoxybenzoyl)diethylgermanium.
Applications of UV Radiation
Published in Jiri George Drobny, Radiation Technology for Polymers, 2020
UV radiation curable dental compositions have been used since the early 1970s.84,85 They consist of photocurable resins with silica filler and offer many advantages: they are ready for use on demand, offer an extended working time, and have an absence of air bubbles, a high polymerization rate, and good color stability. The silica filler provides mechanical strength and reduces shrinkage. However, the formulations have to meet several stringent requirements: The use of light with a wavelength shorter than 330 nm is unacceptable, since it may cause tissue damage and requires that the patient and the operator wear special protective wear. Therefore, photoinitiators for longer wavelengths are used (e.g., camphorquinone).83 The material should be polishable, opaque to X-rays, and stable toward saliva, beverages, etc. Methacrylates are used as the base resin, in spite of their slow cure rate when compared to acrylates, which are less favorable because of their toxicological properties.
Characteristics of Polymers and Polymerization Processes
Published in Manas Chanda, Plastics Technology Handbook, 2017
The dental resins are commonly based on the highly viscous bisphenol A glycidyl methacrylate (abbreviated as bis-GMA, also known as Bowen's monomer after the inventor) have been used for over four decades. Because of its high viscosity (1,369 Pa.s), bis-GMA is blended with diluent, lower molecular weight monomers, to provide a workable matrix resin for composites, for example, bisphenol-A dimethacrylate (bis-DMA), ethylene glycol dimethacrylate (EGDMA), and triethylene glycol dimethacrylate (TEGDMA). Camphorquinone (CQ) is traditionally used as photosensitizer for dental composites. It undergoes a redox reaction with a tertiary amine to produce radicals for free-radical polymerization of the acrylate resin. In a typical procedure, a mixture of bis-GMA and TEGDMA with 1 wt% of CQ and tertiary amine is photopolymerized using visible light device with an intensity of 900 mW/cm2. The photopolymerization of the dental resin is fast with most of the reaction taking place within 40 s, causing gelation and vitrification accompanied by shrinkage of about 8%. Shrinkage continues, as also stiffening, during post-polymerization at a much slower rate (see Table 1.22).
Physical-chemical characterization and bond strength to zirconia of dental adhesives with different monomer mixtures and photoinitiator systems light-activated with poly and monowave devices
Published in Biomaterial Investigations in Dentistry, 2022
Constantino Fernandes Neto, Mayara Hana Narimatsu, Pedro Henrique Magão, Reginaldo Mendonça da Costa, Carmem Silvia Pfeifer, Adilson Yoshio Furuse
As regards the photoinitiator systems, classical systems are based on camphorquinone and tertiary amines [10,18]. Camphorquinone is known to be energized by photons of visible light in the range of 400–500 nm, with absorption peak at 468 nm [19], forming an exciplex complex with amine, which generates free radicals responsible for triggering the polymerization reaction [7]. Tertiary amines are essential for the occurrence of polymerization reaction and variations on the type and concentration of these molecules were reported to influence the DC [8,20]. However, some studies have demonstrated enhanced chemical and mechanical properties with the addition of onium salts as a third component in hybrid photoinitiator systems containing camphorquinone and amine [13,21]. Among these photoinitiators, diphenyliodonium hexafluorphosphate (DPIHP) can be added to the conventional CQ/amine system and was reported to provide higher DC [22,23]. These three-component photoinitiator systems generate two initiating free radicals and one initiating cation by a series of electron transfer and proton transfer reactions [24]. Mechanisms suggested for the DPIHP molecule are that carbon-iodine bonds are cleaved by light, reacting with the CQ/amine complex, generating further free radicals that will trigger the polymerization [25,26]. Additionally, aryl sulphonic salts such as triarylsulfonium hexafluoroantimoniate (TAS-Sb) have been also reported to play an important role as a latent catalyst in cationic polymerization, becoming a potential molecule to be added to triple photoinitiator systems [27,28]. However, its application in dental polymers has not been investigated. TAS-Sb is fast curing, soluble in most monomers, such as vinyl ethers and other vinyl monomers, but insoluble in H2O [28]. Both DPIHP and TAS-Sb are photoinitiators with different wavelength absorption peaks than CQ, in the UV range, between 220 and 350 nm [29–31]. Hence, further studies evaluating the behavior of adhesive compositions with different monomer mixtures and photoinitiator systems are an alternative to provide better polymerization and superior bonding to Y-TZP.