Interactions in reinforced composites as obtained through inverse gas chromatography (iGC)

Good morning, afternoon and evening for everyone. Today's webinar is about interactions in reinforced composites as obtained through inverse gas chromatography. And here's the structure of my presentation. So first I will just talk about the reinforced composites and some little inside of composite industry, some important parameters of composites and introduction of igc. And at the end, which is basically the major part of my presentation, I will present some case studies. Reinforced composite contain reinforcement material which gives the necessary stiffness and strength to the composite. They are multi component systems and their mechanical properties can be correlated with the adhesion between surfaces. Composites can be categorized based on the matrix material or the number of reinforcement materials in it. And in this case you can see a categorization based on the reinforcement material. There's also other categorization out there. Mainly composites can be reinforced with a particle or a fiber or there can be a structural reinforcement. Composite market has an increasing trend in the last decades. And the major drivers for growth in this market are increasing demand for lightweight materials in the aerospace and defense and automotive industries. And based on the statistic, automotive industry will show significant increase in lightweight material usage till 2030. It's estimated also that the overall lightweight market in automotive will increase from 70 to 300 billion euro, reflecting an annual growth rate of 8% till 2030. Lightweighting is an important end use energy efficiency strategy in transportation. Carbon fiber and other lightweight materials will develop across industries and especially in automotive industry. This increasing trend on base materials a result of presence of new suppliers and increasing demand on product quality and also a new trend of recycling carbon fiber. The recycled carbon fiber quality is not the same as the virgin carbon fiber. It has a lack of sizing and some potential residues of chair and resin may left on the fiber. Surface residues will tend to lead poor fiber and matrix adhesion. And for all these reasons and for some others as well, the importance of surface characterization and more detailed information about the physical and chemical properties of the materials will come into view. The good adhesion between the matrix and the filler is crucial in reinforced composites. The quality and performance of nanocomposites depend strongly on the interactions of the components and their interface. Surface treatments and modifications of fibers or fillers performed to enhance this adhesion. Surface energetics of the individual components can be related to the adhesion. Performing contact angle studies to measure surface energy on fibers, powders or on paper is difficult because of the irregular surface, small substrate size for fibers and weakening phenomena. IGC inverse gas chromatography doesn't suffer from those limitations, IGC was developed in the 60s and it's mainly used to measure surface energetics of solid materials. Nevertheless, it's suitable to determine other physical chemical properties of solid materials especially suited to fibrous and powdery substrates. IGCSE is the first and the only commercial IGC system is produced by sms. On this slide you can see the schematic of the IGC SCA system. The carrier gas is helium or nitrogen. The oven has a special design to determine thermodynamic properties and there's two column positions that you can see also on the picture on the left side and the standard oven has a 2250 degrees Celsius operating range and it has an alternative gas phase injection system which provides a precise injection of a wide range of injectable probes and also it has a very user friendly control and analyzer software. Our IGCSE system is equipped with fid, which is the most sensitive detector for organic vapors, but it's not sensitive for water. Therefore we can provide the system with the background humidity controller which can generate humid carrier gas flow through the system through the column and the influence of the relative humidity on the different physicochemical properties can be measured with igcsea. It's quite important benefit of our instrument because there's humidity everywhere during production, during storage and during the application of the solid material. IGC SCA column is different compared with the classic GC column. Our sample column are straight selenized glass tubes with different inner diameters. So you can select the most suitable diameter or the sample and the columns are not reusable. But RGC measurements is a non destructive analysis so you can use a packed column for different type of analysis. For example, in case of fibers we use the 4 milli diameter column inner diameter column and we don't chop the fiber. We use a quite long piece of the fiber, create a heart and then pull or push into the in the column. If you are interested in the column packing, you can visit our YouTube channel and you can see column packing procedures in case of powders and fibers. This slide shows the difference in principle between analytical GC and and igc. While GC is used to get quality and quantity information about the injected compounds, IGC is used to get physicochemical information about the solid material which is packed into the column. The sample of interest is packed into the column and single pure organic probes injected onto the column. The retention time of the different organic probes is measured which indicates the interaction strength between the surface and the Probe and also it can be used to determine different physicochemical properties of the solid material which is in the column. For example, to measure the dispersive surface energy series of normal alkanes injected one by one through the column from the retention parameters, the dispersive surface energy can be calculated using the Schulz or the Dorisen Gray method. This gives a single surface energy value for us. So if we inject a very small surface coverage, we can determine the surface energy at a very small concentration, also called infinite dilution, increasing the concentration of the alkanese but still being in the concentration range, whereas the solute concentration is very low, reflecting the solid and solute interactions. So if we increase the concentration but still being in this concentration range, where it's only solid solid interactions appear, we can determine the surface energy profile and from the surface energy profile we can get the surface energy distribution from so we can determine how heterogeneous is the surface energetically. Because real material surface are often heterogeneous due to the surface defects or some impurities on the surface, injecting only a single probe at different concentration, the adsorption isotherm can be determined and from the adsorption isotherm, the bed specific surface area or the sorption capacity or Henry's adsorption constant can be also determined. This slide lists the most commonly measured properties of composite compounds using idc. For example, surface density and acid base properties are often determined of composites because a high surface energy means a more reactive surface, which has important implications in processes involving interfacial interaction that happens in wetting, coating mixing, compaction, cohesion and adhesion. And also surface energy can be related to surface adhesion, enhancing treatments and adhesion with other substrate bet. Specific surface area is also often measured with IGC on composite compounds, especially on fibers and fillers and fiber matrix and filler matrix. Specific interaction parameter is also property what you can determine with IGC and it's determined from the acid and base constants of the individual components and this specific interaction parameter has a linear relationship with the interfacial shear resistance and is also used to rationalize the acid base forces at pigment resin interfaces. Once we know the surface energy of the individual components, the thermodynamic work of adhesion and cohesion can be calculated. So if we have two components, Component 1 and Component 2, and we measure the surface energy components, the dispersive and the acid and base components, we can determine the work of adhesion between those components and also we can determine the work of cohesion of the particles. The individual particles cohesive energy will correlate with the aggregation affinity of the particles. So aggregation sample. The first case study is on composites and it was a collaboration with nist. Quality and performance of nanocomposite depend strongly on the interaction of the components at their interface. To enhance the adhesion properties at the interface. Nanomaterials are often exposed to various surface functionalization processes. Two different types of nanomateria, carbon nanotubes and nanoclay was investigated in this study. The carbon nanotube was oxidized to create functional groups and to activate the surface. Whereas the nanoclay was passivated with the surface treatment which was applied on it. We are looking at two different materials and two different surface treatments and investigate the effect of these surface treatments on the surface properties. The total surface energy of the nanomaterials and the polyurethane is presented on this slide. Clearly, the surface treatment had significant effect on the surface energy of these materials. You can see that the S received nanoplay has a really high surface energy. After the treatment, the treated nanoclay is a significantly lower, smaller surface energy. Opposite trend can be observed on the carbon nanotube samples. The oxidation this surface treatment increased the surface energy of the carbon nanotube. With higher surface energy of the oxidized carbon nanotube and the S received nanoclay, the greater the cohesive forces between particles. Very strong particle particle interactions leads to poor dispersion. So once we have the surface energy components of the individual materials, you can calculate the cohesion and adhesion and adhesion energy between polyurethane and each pillars were calculated and also the cohesive energy. And from these two energies, the ratio was also determined either higher this ratio or closer to one is better and means a good adhesion and a good performance. Good composite performance in case of. In case of carbon nanotube, the S received showed better ratio than the oxidized carbon nanotube. And in case of the nanoplay, we can select the functionalized nanoplate which shows better ratio. Using surface energy, these two fillers can be selected as a promising reinforcement material or polyurethane matrix. Our collaborator nist, they actually made the composites and tested the mechanical properties of the actual samples and two composites. Composites showed improved mechanical properties the same two composites, whereas the adhesion and cohesion ratio was better. So, using surface energy and adhesion in the early stage of development, the most promising fillers or fibers can be selected for the polymer matrix. In the next case study, which was also A collaboration with Deakin University and this was on a ultra fine silk particles Silk has a long history and recently its application is expanded. Some examples like filler in synthetic fibers and polymeric products. Biomedical applications also recently quite popular filler in composite scaffold. Using silk powder improves moisture management, handling and dyeing and functional properties in such products. And it's lightweight processing and application of silk requires a good understanding of their bulk properties such as cohesiveness, flowability, spreadability, aggregation and dispersion. In this study we used air silk which is not that popular in textile industry. However, the host plant is available in wide climate conditions and it's more disease resistant. So we investigated three silk powders and the fiber. The sample labeled with F was a decal fiber. AM sample was decalmed, cotted, milled and spray dried to get powder form. And then we used this AM powder and applied air jet milling on this. And we had this AM AGM sample and the last sample ITAM was a little bit different than the AM sample. In this case, intensive decoming was applied in only three hours milling. On this slide you can see some images and the BET specific surface area values measured using IGCSEA and also the average particle size from laser diffraction results. So you can see that the AM silt powder has a 5 micron average particle size. The calculated surface area of a solid 5 micron sphere should be about 1 meter square per gram surface area. You can see that measured the experimental surface area is much higher. It's 18.57 meter square per gram is very close to the value what we measured. Also that we measured with the nitrogen absorption technique. So this sample surface area was also determined with nitrogen absorption method and the results with IGC and nitrogen absorption technique. We're in a really good agreement. The much higher experimental BET surface area of this AN sample indicates that the particles are not solid sphere, but their morphology is distinctly different. So what we clearly could see on the image of the AM sample particles, the AM particle surface have like a cauliflower like granular morphology. The air jet milling so the same AM sample but applying air jet milling on it. So the air jet milling process sharply reduced the average particle size. So from 5 micron to 700 nanometer. But you can see that there's no significant increases in the surface area. It was assumed that there was fragmentation of the particles during air jet milling. Size reduction was achieved mostly due to the DE aggregation of primary particles from AM particle aggregates and then the last sample ideam. The surface area of this Sample is significantly different than the AM particles despite having the same average particle diameter. A much lower surface area is the result of the different particle morphology. It doesn't have granulated surface and porous architecture like the AM sample. The silk powder on this slide you can see the surface energy results of the silk powders and the fiber. The fiber is the F and the others. The colored lines and dots presents the different silk powders. What we can observe that the silk powder has higher surface energy than the fiber. The silk fiber results of this study confirmed that chemical processing altered the surface energy of silt powders. And also we can observe that the air jet milled cell powder shows higher surface energy total surface energy due to its higher specific surface energy. Higher surface energy also means higher cohesive energy as well. So the particle particle interactions is quite strong. In case of the edge at mill silk powder. The cohesion and flow function results determined from the Schar test show the same trend. Air jet milled silk powder is highly cohesive and less flowable. Based on the flow function number, the air jet milled powder is also considered as a very cohesive powder. In a final conclusion, we can say that surface energy could be correlated with the cohesiveness and the flow behaviors of silk powders. In the next case study, we investigated carbon fibers. The aim of this study was to determine the effect of surface treatments on surface properties of fibers and on adhesion with the polymers. Three different carbon fibers and three different polymers were investigated. The difference between carbon fibers was that the sample label with CA was an unsized and unoxidized sample. And we had also an oxidized carbon fiber and finally an oxidized emphasized carbon fiber. The surface energy of these samples presented on this slide, the dispositive part of the surface energy. You can see that the oxidized carbon fiber has significantly higher surface energy than all the other samples. Which means it's a really active sample. The surface is very active. And also what you can see that the sized carbon fiber has a significant lower surface energy, even lower surface energy than the untreated carbon fiber. The reason is that the formation of the of this epoxy layer resulted less active surface. The surface treatment also changed the acid and the base properties of the carbon fibers. While the surface of the untreated carbon fiber is more basic in nature, the oxidized and then the sized carbon fiber shows more acidic surface in nature. Different acid base properties affects the fiber matrix interaction strength which was supported by the adhesion and the interfacial shear test results. And you can see on this graph the adhesive energy and the interfacial shear as your test results. The oxidized carbon fiber with all the three polymers has higher adhesion and interfacial shear stress values. The both properties, the adhesion and the interfacial shear stress increased. Third, untreated sizing did not really increase the mechanical performance despite the higher adhesive energy. What we find for these composites, the interferometers field trace obtained, that's carried out. And in the final conclusion we can tell that the surface treatment affects surface properties of the different reinforcement materials. And the surface properties affect the adhesion between the matrix and the reinforcement material. The end properties of a composite part depend on the matrix, reinforcement material and their starting forms. ITC is the most suitable technique for fibrosis and powdery substrates and to characterize the surface composite components because it doesn't suffer from those limitations like other surface characterization technique. And it's a quick, accurate, versatile technique and very user friendly to characterize different kind of solid materials. And finally, I would like to recommend the handbook of adhesive technology. So especially the chapter five which described the acid base interactions in composites and the adhesion, the importance of adhesion. There's also some publications on IGCSEA using cellulose, on cellulose and polymer composites. And there's also some other cellulosic fibers, surface energy and surface area. So thank you for your attention and special thanks to our collaborators and I'm ready to answer your questions.

Yes, thank you so much, Annette. If you have any questions, just. Just let us know. You can put it in the chat box or you can ask Ana therapy.

Yes, I have a question. So in terms of the analysis, what's the temperature limitation of the system?

The standard oven has a 2250 degrees C operating range. However, we have high temperature oven up to 500 degrees C. It's just under development. The first prototype has been shipped to a customer a year ago. But we are ready now to produce this instrument.

So basically it's choosable that do I want it with a standard or with a high temp. Com Oven?

Yeah, exactly, exactly. Most of our customers are in pharmaceutical industry and they they're interested in a lower temperature range. So for them the standard oven or is more suitable and its higher temperature is not really necessary. And we have this high temperature oven which is from 30 degrees C up to 500. So the temperature range is quite wide. However, there's only just one column position due to the bigger insulation. But the instrument required in the oven we had to implement a bit wider insulation due to the temperature, the high temperature. Okay, thank you.

Thank you, Joseph. Thank you, Annette. So there's a question here from Simon, Annette. How does absorbed species affect your surface energy measurements? This could be example water absorbed from the atmosphere. This absorbed species can be displaced later by your polymer matrix.

I mean absorbed species. So impurities on the surface can affect the surface energy. And in that case the surface energy heterogeneity will be wider. Water absorbed water molecules from course also affects the surface energy, because at a certain relative humidity, some water can absorb on the surface. But in our system there's an option to condition the sample at high temperature. So before an experiment, you can completely dry out sample, remove any absorbed gases or water from the surface.

When analyzing a polymer, what operating temperature would you choose with regards to the polymer's glass transition temperature?

It's a good question. It depends the parameter. What you'd like to measure in case of surface energy? I think any temperature which you'd like to measure the surface energy. Or for example, if you'd like to know the surface energy close to the polymer, the TG temperature is recommended. But you can measure at lower temperature or at higher. There's a nice study which shows that there's not too big changes in surface energy in case of polymers along the temperature range close to the TG in case of polymers. That will give you the best the volume, which is much closer to surface energy when you apply the polymer and the filler when you mix them together.

Okay, I think that's about it. If you have other questions, you can email us scienceurfacemeasurementsystems.com or if you want to know more about IGCSEA, you can also visit our website or our YouTube channels where we have videos about IGC. And join us again in the next webinars. So, thank you very much, Annette.

Thank you also for your participations.

Take care. Bye.