Curing is a chemical process employed in polymer chemistry and process engineering that produces the toughening or hardening of a polymer material by cross-linking of polymer chains.[1] Even if it is strongly associated with the production of thermosetting polymers, the term "curing" can be used for all the processes where a solid product is obtained from a liquid solution, such as with PVC plastisols.[2]
Curing process
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Figure 1: Structure of a cured epoxy glue. The triamine hardener is shown in red, the resin in black. The resin's epoxide groups have reacted with the hardener. The material is highly crosslinked and contains many OH groups, which confer adhesive properties.During the curing process, single monomers and oligomers, mixed with or without a curing agent, react to form a tridimensional polymeric network.[3]
In the very first part of the reaction branches of molecules with various architectures are formed, and their molecular weight increases in time with the extent of the reaction until the network size is equal to the size of the system. The system has lost its solubility and its viscosity tends to infinite. The remaining molecules start to coexist with the macroscopic network until they react with the network creating other crosslinks. The crosslink density increases until the system reaches the end of the chemical reaction.[3]
Curing can be induced by heat, radiation, electron beams, or chemical additives. To quote from IUPAC: curing "might or might not require mixing with a chemical curing agent".[1] Thus, two broad classes are curing induced by chemical additives (also called curing agents, hardeners) and curing in the absence of additives. An intermediate case involves a mixture of resin and additives that requires external stimulus (light, heat, radiation) to induce curing.
The curing methodology depends on the resin and the application. Particular attention is paid to the shrinkage induced by the curing. Usually small values of shrinkage (2–3%) are desirable.[2]
Curing induced by additives
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Figure 2: General representation of the chemical structure of vulcanized natural rubber showing the crosslinking of two polymer chains (blue
andgreen
) with sulfur (n = 0, 1, 2, 3 …). Figure 3: Simplified chemical reactions associated with curing of a drying oil. In the first step, the diene undergoes autoxidation to give a hydroperoxide. In the second step, the hydroperoxide combines with another unsaturated side chain to generate a crosslink.[4]Epoxy resins are typically cured by the use of additives, often called hardeners. Polyamines are often used. The amine groups ring-open the epoxide rings.
In rubber, the curing is also induced by the addition of a crosslinker. The resulting process is called sulfur vulcanization. Sulfur breaks down to form polysulfide cross-links (bridges) between sections of the polymer chains. The degree of crosslinking determines the rigidity and durability, as well as other properties of the material.[5]
Paints and varnishes commonly contain oil drying agents, usually metallic soaps that catalyze cross-linking of the unsaturated drying oils that largely comprise them. When paint is described as "drying" it is in fact hardening by crosslinking. Oxygen atoms serve as the crosslinks, analogous to the role played by sulfur in the vulcanization of rubber.
Curing without additives
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In the case of concrete, curing entails the formation of silicate crosslinks. The process is not induced by additives.
In many cases, the resin is provided as a solution or mixture with a thermally-activated catalyst, which induces crosslinking but only upon heating. For example, some acrylate-based resins are formulated with dibenzoyl peroxide. Upon heating the mixture, the peroxide converts to a free radical, which adds to an acrylate, initiating crosslinking.
Some organic resins are cured with heat. As heat is applied, the viscosity of the resin drops before the onset of crosslinking, whereupon it increases as the constituent oligomers interconnect. This process continues until a tridimensional network of oligomer chains is created – this stage is termed gelation. In terms of processability of the resin this marks an important stage: before gelation the system is relatively mobile, after it the mobility is very limited, the micro-structure of the resin and the composite material is fixed and severe diffusion limitations to further cure are created. Thus, in order to achieve vitrification in the resin, it is usually necessary to increase the process temperature after gelation.
When catalysts are activated by ultraviolet radiation, the process is called UV cure.[6]
Monitoring methods
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Cure monitoring is, for example, an essential component for the control of the manufacturing process of composite materials. The material, initially liquid, at the end of the process will be solid: viscosity is the most important property that changes during the process.
Cure monitoring relies on monitoring various physical or chemical properties.
Rheological analysis
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Figure 4: Evolution in time of storage modulus G' and loss modulus G" during a curing reaction.A simple way to monitor the change in viscosity, and thus, the extent of the reaction, in a curing process is to measure the variation of the elastic modulus.[7]
To measure the elastic modulus of a system during curing, a rheometer can be used.[7] With dynamic mechanical analysis, the storage modulus (G') and the loss modulus (G) can be measured. The variation of G' and G" in time can indicate the extent of the curing reaction.[7]
As shown in Figure 4, after an "induction time", G' and G" start to increase, with an abrupt change in slope. At a certain point they cross each other; afterwards, the rates of G' and G" decrease, and the moduli tend to a plateau. When they reach the plateau the reaction is concluded.[3]
When the system is liquid, the storage modulus is very low: the system behaves like a liquid. Then the reaction continues and the system starts to react more like a solid: the storage modulus increases.
The degree of curing, α {\displaystyle \alpha } , can be defined as follow:[8]
α = G ′ ( t ) − G m i n ′ G m a x ′ − G m i n ′ {\displaystyle \alpha ={\frac {G'(t)-G'_{min}}{G'_{max}-G'_{min}}}} [8]
The degree of curing starts from zero (at the beginning of the reaction) and grows until one (the end of the reaction). The slope of the curve changes with time and has his maximum about at half of the reaction.
Thermal analysis
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If the reactions occurring during crosslinking are exothermic, the crosslinking rate can be related to the heat released during the process. Higher is the number of bonds created, higher is the heat released in the reaction. At the end of the reaction, no more heat will be released. To measure the heat flow differential scanning calorimetry can be used.[9]
Assuming that each bond formed during the crosslinking releases the same amount of energy, the degree of curing, α {\displaystyle \alpha } , can be defined as follows:[9]
α = Q Q T = ∫ 0 s Q ˙ d t ∫ 0 s f Q ˙ d t {\displaystyle \alpha ={\frac {Q}{Q_{T}}}={\frac {\int _{0}^{s}{\dot {Q}}\,dt}{\int _{0}^{s_{f}}{\dot {Q}}\,dt}}} [9]
where Q {\displaystyle Q} is the heat released up to a certain time s {\displaystyle s} , Q ˙ {\displaystyle {\dot {Q}}} is the instantaneous rate of heat and Q T {\displaystyle Q_{T}} is the total amount of heat released in s f {\displaystyle s_{f}} , when the reaction finishes.[9]
Also in this case the degree of curing goes from zero (no bonds created) to one (no more reactions occur) with a slope that changes in time and has its maximum about at half of the reaction.[9]
Dielectrometric analysis
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Conventional dielectrometry is carried out typically in a parallel plate configuration of the dielectric sensor (capacitance probe) and has the capability of monitoring the resin cure throughout the entire cycle, from the liquid to the rubber to the solid state. It is capable of monitoring phase separation in complex resin blends curing also within a fibrous perform. The same attributes belong to the more recent development of the dielectric technique, namely microdielectrometry.
Several versions of dielectric sensors are available commercially. The most suitable format for use in cure monitoring applications are the flat interdigital capacitive structures bearing a sensing grid on their surface. Depending on their design (specifically those on durable substrates) they have some reusability, while flexible substrate sensors can be used also in the bulk of the resin systems as embedded sensors.
Spectroscopic analysis
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The curing process can be monitored by measuring changes in various parameters:
Ultrasonic analysis
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Ultrasonic cure monitoring methods are based on the relationships between changes in the characteristics of propagating ultrasound and the real-time mechanical properties of a component, by measuring:
See also
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References
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So, you’ve decided to tackle your kitchen or bathroom and resurface those old countertops. It may or may not be your first time working with epoxy and knowing some of the ins and outs of the resurfacing process can save you that avoidable headache. To help ease that process we have put together some general Do’s and Don’ts for epoxy countertop resurfacing to help you avoid those small mistakes and achieve those dream countertops.
DO
DO
DO
DO
Epoxy Surface Preparation for the 5 most common countertop surfaces
What surfaces You Can (and Cannot) Resurface with Epoxy
DO
DO
You can Refer to our epoxy coverage chart under our Premium FX Poxy product description here.
DO
be aware of product cure times. Our Premium FX Poxy but keep in mind it takes a full 30 days to cure to it's full durability. We always recommend to "baby" your new countertops for the first couple weeks. Meaning, don't set any heavy objects that may leave impressions (such as crock-pots or items with 'feet' on them) or try and test out the scratch/heat resistance during the first 30 days.be aware of product cure times. Ourwill cure to a useable hardness within 12-24 hourskeep in mind it takesto cure to it's full durability. We always recommend to "baby" your new countertops for the first couple weeks. Meaning, don't set any heavy objects that may leave impressions (such as crock-pots or items with 'feet' on them) or try and test out the scratch/heat resistance during the first
DO
Practice - Pour a small sample piece first. Great for getting your technique down before the big pour and deciding what design details work for you and ones that don't. Not sure about committing to a big project just yet or first time working with epoxy? Order ourPractice - Pour a small sample piece first. Great for getting your technique down before the big pour and deciding what design details work for you and ones that don't. Not sure about committing to a big project just yet or first time working with epoxy? Order our FX Test Kit and try out our product before committing to that big one.
DO
Ask questions – Send us a message on social media, email our team atAsk questions – Send us a message on social media, email our team at info@countertopepoxy.com or call our office 970.639.9338 and speak with us directly. Our office is open M-F, 8am-6pm Mountain Time and our representatives are more than happy to help answer any questions for you or even walk you through the whole process from start to finish!
Read our Frequently Asked Questions
DO
Take pictures – Take those before and after shots of the whole process. Remember the process that gave you that beautiful transformation, nothing beats wowing your friends and family with those before and after photos!
DO
Acclimate your product and ambient temperature - It's extremely important before pouring your epoxy surface to make sure product and ambient temperature is acclimated to 70- 75 degrees Fahrenheit. If improperly acclimated and temperatures are below 70 degrees F, it will result in a soft cure that's not durable. Do check your product temperature, home thermostat and even your surface temperature before pouring. While your space may be at 70 degrees F, your countertop surface can be at a lower temperature. Bring your room and epoxy to 70-75 degrees F, for 2-3 days before you pour. Once you have poured, it is important to maintain this temperature for another 24 hours to allow for the countertop to cure properly.DO
Watch Video Tutorials - Researching and learning all you can before starting your project will ultimately give you the best results. Do watch our tutorial videos to learn more about our product, the designs, techniques, and tips and tricks to help you with every aspect of the project.Our YouTube Channel, CountertopEpoxy
Epoxy Kitchen Countertop How To
Countertop Edges and Epoxy Surface Coating Tips
How to De-Gloss and Polish an Epoxy Countertop
How To: Create an Epoxy White Marble Countertop
How To: Create Slate Gray Countertops
How to Create a Wood Grain Epoxy Countertop
How to Create a Butcher Block Countertop with an Epoxy Coating
DON'T
DON’T
Rush the mixing process - The mixing process is the most vital step in ensuring your product cures properly. Rushing or improperly mixing the epoxy at its intended ratio (Rush the mixing process - The mixing process is the most vital step in ensuring your product cures properly. Rushing or improperly mixing the epoxy at its intended ratio ( Premium FX Poxy is a 1:1 Ratio) is a common mistake most DIYer's make. Make sure to follow the instructions for the mixing time and ratio of the product. If improperly mixed, it can result in soft spots or tacky areas that will not cure.
Read our detailed Countertop Instructions.
Watch our Video on How To: Mix our Premium FX Poxy, Add FX Prime Coat, and FX Metallic Powders.
DON’T
Under estimate product amount – So you’ve measured out your surface and got your square footage, now time to order enough product to cover your surface. Let’s say you have 42 sq. ft. of countertop you want to resurface. Our Do not under estimate product coverage. We recommend getting the right amount for every square foot of your surface, cutting corners on product amount can result in dents, divots or fisheyes. This happens from the product pulling too thin in areas without enough product. The more product you have for your square footage will ultimately save you from worry. In this case of 42 sq. ft., we'd recommend 2.5 Gallons of product which will give you a total coverage of 42-50 sq. ft. This allows you to not only have more than enough product but ensures your surface will be fully and properly covered. The more the merrier.Under estimate product amount – So you’ve measured out your surface and got your square footage, now time to order enough product to cover your surface. Let’s say you have 42 sq. ft. of countertop you want to resurface. Our 2 Gallon Premium FX Poxy Kits will cover 32-40 sq. ft, you may be thinking "2 Gallons should be enough, it’s only 2 sq. ft. over". Wrong.. We recommend getting the right amount for every square foot of your surface, cutting corners on product amount can result in dents, divots or fisheyes. This happens from the product pulling too thin in areas without enough product. The more product you have for your square footage will ultimately save you from worry. In this case of 42 sq. ft., we'd recommend 2.5 Gallons of product which will give you a total coverage of 42-50 sq. ft. This allows you to not only have more than enough product but ensures your surface will be fully and properly covered. The more the merrier.
How much epoxy do I need to cover my floor, countertop, or wall?
Why do I have dents or divots in my epoxy countertop?
DON’T
How To: Create veins in Epoxy Countertops
DON'T
neglect your ambient temperature - While you acclimated everything properly, don't neglect keeping your ambient temperature at the appropriate 70-75 degrees Fahrenheit during application and after. If your work space temperature exceeds or deeps under the proper work temp, it can have some unfortunate effects. Too warm/hot will result in product curing much quicker than anticipated and lessening your work time significantly. Too cold and the product will not cure to it's full hardness or at all.
DON'T
excessive product sitting in your mixing container. By doing so, the excessive amount of product left in the container will flash, bubble, heat up, cure at an extremely fast rate and potentially crack. Once the product is properly mixed, pour it out on your surface immediately. Same can be said for pouring ourleaveproduct sitting in your mixing container. By doing so, the excessive amount of product left in the container will flash, bubble, heat up, cure at an extremely fast rate and potentially crack. Once the product is properly mixed, pour it out on your surface. Same can be said for pouring our Premium FX Poxy thicker than the intended 1/8 inch thickness. If wishing to pour thicker, you can pour multiple 1/8" layers (letting each layer cure 12-24 hours between), or opt for our FX Casting Resin which can be poured at an 1 inch thickness in a single pour.
DON’T
over work your surface – Once you pour the product out you want to spread the product across in smooth even strokes. Don’t overwork the area or treat it as painting. Take your time in ensuring the product is level across your entire piece and let the epoxy do the work.
Refer to our post on Vertical Edges and Surface Coating Tips.
DON’T
over torch - While popping bubbles is extremely satisfying, you can potentially over torch your surface and cause epoxy burns or unfortunate amber torch marks showing up after cure.
How to Properly torch your epoxy surface
DON’T
Following these Do's and Don'ts will help make your project go as smooth as possible. Do you have a question about the process? Please don't hesitate to reach out by giving us a call 970.639.9338 or sending our team an email at info@countertopepoxy.com. We are happy to be of service!