News and Publications

Find out latest news from Nordkalk

Nordkalk Enrich ultrafine PCC enables high performance at high PVC

Matti Lammela Application Manager, R&D Nordkalk, 18 June 2020

Calcium carbonate is a widely used material in many industries e.g. paints and plastics. Usually it is used as a filler to get savings in raw material costs. Generally, it cannot be added in large amounts due to weakening effect of crucial properties such as optical and mechanical properties. How filler behaves is strongly related to its surface properties, such as dispersibility and viscosity of the suspension. Several types of nano-PCC (precipitated calcium carbonate) products are in the market, however, their uses are often restricted to special applications. New product Nordkalk Enrich® is created to break this allegation.

Enrich enables high filler loadings without compromising quality. Enrich is also sustainable substitute for traditionally used pigments and crude oil based binders. Furthermore, the multifunctional filler gives rise to new possibilities and performances. The study below demonstrates the potential of multifunctional filler in several applications.

The unique properties of Nordkalk Enrich

Nano-PCC with primary particle size of e.g. 50 nm has been known and produced in decades. However, the usage of the product has been limited due to the strong agglomeration of the particles. Hence, the true nano scale properties potential have never been really explored until now. A novel nano-PCC product, developed by Nordkalk Corporation is illustrating superior properties and performance. Figure 1 illustrates the particle size distributions of conventional GCC, conventional nano-PCC and Nordkalk Enrich.

The conventional GCC has wide particle size distribution and median particle size is 2.5 µm. Minority of particles of conventional nano-PCC are between 0 – 500 nm but the majority of particles are between 1 – 10 µm. Median value for conventional nano-PCC is 3.8 µm and d90% value is 7.2 µm. The particle size of Nordkalk Enrich is between 0 – 500 nm. For Enrich the median is 110 nm and d90% is 240 nm. The figure shows that Enrich has much narrower particle size distribution than conventional nano-PCC. The optimal size of Enrich particles, close to the half of wave length of the visible light, gives very good hiding power.

Enrich article Figure 1

Figure 1. Particle size distributions of conventional GCC, conventional nano-PCC and Enrich measured with Beckman Coulter LS 13 320 laser diffraction particle size analyzer.

Scanning electron microscope (SEM) pictures of conventional GCC (Picture 1a), conventional nano-PCC (Picture 1b) and Nordkalk Enrich in a styrene acrylate matrix (Picture 1c) verify the results that the previous particle size distribution results illustrate. SEM pictures were made 1:9 mixes from GCC binder, conventional nano-PCC and binder and Enrich and binder which were mixed 10 minutes with tooth disk agitator. After mixing 200 µm films were prepared and pictures were taken from the films with Zeiss Supra 55VP scanning electron microscope. In the SEM picture you can see that the conventional nano-PCC particles are in large agglomerates. In Picture 1c can be seen well dispersed Enrich particles in primary form or in very small agglomerates. This very good dispersibility enables higher loadings without affecting crucial parameters. Enrich is surface modified with a surfactant which sterically and electro statically prevents re-agglomeration. 

Enrich article Picture 1 1000px

Picture 1 a,b,c. SEM picture (back scatter diffraction method) of a) conventional GCC, b) conventional nano-PCC and c) Nordkalk Enrich in polymer matrix.

These narrower well dispersed Enrich particles can be seen in picture 2 below, comparing a) Enrich and b) conventional nano-PCC. In comparison there can be seen also better surface quality and less cracks caused by GCC, which is also present in these PVC formulations. 

1 2

Picture 2. A) PVC filled with Enrich B) PVC filled with conventional nano-PCC 

In order to emphasize the nanorange particle size and the easy dispersibility, Nordkalk Enrich and conventional GCC (ground calcium carbonate) micro filler (d50 % 2.5 μm) were compared in a high gloss indoor paint. The commercial indoor paint was filled with Enrich and GCC filler. Series were made by adding these fillers in to ready paint. They were added by different percentage of dry mass the paint. Dry solid contents in the ready paint and the added filler slurry were the same so consequently, the resulting mix had the same dry solid content. After mixing, 200 µm thick films were prepared, dried for 48 hours and after drying the specular glosses were measured according to standard ISO 2813 with the Zehntner ZLR 1050 M gloss measuring device.

Figure 2 demonstrates gloss as a function of different percentages of filler. Without added filler the gloss (measuring angle 60°) was about 85 %. When GCC is added by 5 % of mass the gloss drops dramatically to value under 50 %. With Enrich the gloss stays almost the same as without filler. When you add 25 % of GCC by mass the gloss has dropped under 10 %. With Enrich the gloss stays over 70 % even if it is added by 40 % of mass. The results correspond to the theory that small particles forms smoother film and the particles pack tighter. This enables higher gloss even with higher PVC’s.

Enrich article Figure 2

Figure 2. Gloss values of commercial high gloss indoor paint filled with different percentages of Enrich and conventional GCC.

Enrich in other applications

Nordkalk Enrich provides new formulating opportunities also in several other applications. As a multifunctional filler Enrich can improve several properties and at the same time be cost efficient. Next will be shortly introduced highlights from adhesives, sealants, plastics and rubbers. Enrich has also shown potential in fire retardation and paper applications.

Adhesives and Sealants

Fraunhofer Institute in Germany has investigated the suitability of Enrich in adhesives and sealants. Even with the small quantities of Enrich the required properties (viscosity, no sedimentation during storage, application ... ) are achieved in combination with higher tensile strength at 100% elongation (2 fold), higher elongation at Fmax (4 fold), higher elongation at break (3 fold), lower modulus of elasticity at room temperature and very good hydrolysis resistance. Higher tensile strength can be seen in Figure 3. Out of these properties named before, Enrich has also shown reduced drying time in water proofing applications. 

Enrich article tensile strengths

Figure 3. Tensile strengths of Enrich and ground calcium carbonate in polyvinyl acetate based adhesive.

Plastic and Rubber

In plastic and rubber Nordkalk Enrich enables higher filler loadings. As it has been already presented in the beginning of the article (Picture 2 a and b) one can see how conventional stearate coated nano-PCC is badly dispersed compered to Enrich. Better dispersibility leads to higher gloss which can be seen from Figure 4.

Enrich Gloss comparison

Figure 4. Gloss comparison of PVC filled with Enrich and competitor (conventional nano-PCC)

Figure 5 illustrates how gloss of PVC increases when it is filled with Enrich. At the same time the impact strength stays more or less on the same level when total filler loading is increased almost by 50%.

Enrich PVC filled with different loadings of Enrich

Figure 5. PVC filled with different loadings of Enrich 

Conclusion

Results show that in coatings applications high PVC values can be achieved without comprising with technical performance by adding Enrich. With Enrich binder and TiO2 has been partly replaced in high glossy indoor paint and traditional gloss outdoor paint and still were achieved desired gloss and hiding power. In indoor paints gloss 20 and 7 the tailored formulations with the higher PVC has given as good results as reference formulations with lower PVC. The critical values has remained the same and wet-scrub abrasion results has been maintained in class 1. Tailored formulations have covered all the properties they should. In floor paint the binder has been partly replaced with Enrich and also the hard binders has been changed to softer ones. The shift from harder binders to softer hasn’t weakened abrasion resistance. In the case of acrylate binders the shift from hard to soft with Enrich in the formulation has even demonstrated superior abrasion resistance properties.

Enrich has shown its multifunctionality also in other applications including adhesives and plastics. Higher filler loadings are possible when using Enrich, still maintaining required properties. Some properties can be even improved in a cost effective way.

 

Leader in Northern Europe

Nordkalk is the leading limestone company in Northern Europe. We deliver essential raw materials to numerous industries, and our solutions contribute to clean air and water as well as productivity of agricultural land.