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Issue 06/2018

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bioplasticsMAGAZINE_1806

Materials Modified

Materials Modified Calcium Carbonate opens new opportunities for the use of PLA P olylactic Acid (PLA) is one of the fastest growing biobased polymers on the market. Processors have tried to use Calcium Carbonate to improve properties and the cost structure, as is common in conventional polymers. Omya gained experience showing that conventional Calcium Carbonate can lead to the degradation of PLA and PLA / PBAT blends used in products such as cups, trays, lids and bags. Omya followed market demand to develop a new type of Calcium Carbonate that does not cause PLA degradation. Introduction PLA is a bio-polyester which degrades when processed with moisture due to hydrolysis. Calcium Carbonate is by nature a somewhat hygroscopic material and carries a certain amount of moisture on its surface and in its crystal structures. In 1952, Omya launched the first surface-treated Calcium Carbonate with reduced moisture adsorption. Today it is common to use surface-treated calcium carbonate in all types of polymer applications to prevent processing problems and surface defects on the final products. The most common surface treatment materials are based on fatty acids, such as stearic acid. With such a treatment, a good reduction of the moisture uptake on the Calcium Carbonate can be observed, but it ultimately causes hydrolysis in PLA. With the development of Omya Smartfill ® technology, the situation has changed. It is now possible to add 40 % or more of Calcium Carbonate in films, sheets or injection molded parts without causing significant hydrolysis while improving important properties such as elongation, stiffness and impact. Product Evaluation Melt flow rate is considered a good indicator of polymer chains degradation: As PLA degradation increases, it is expected that the melt flow rate of the polymer or compound would increase too. Table 2 shows the difference between conventionally treated Omyacarb ® 1T and Omya Smartfill after preparing a 40 % Calcium Carbonate compound with Natureworks Ingeo 2003D. The compounding line is a continuous kneader without vacuum degassing and only pre-dried PLA was used. The results show that using a conventional Calcium Carbonate, such as Omyacarb 1T, MFR increased significantly, which means that important polymer degradation has taken place during processing. In contrast, Omya Smartfill does not show signs of degradation and kept the melt flow on the same level as virgin PLA. A more common technology for processing PLA is twinscrew compounding with the ability to extract water by vacuum degassing. Table 3 shows that in these processing conditions, the melt flow rate increase with Omyacarb 1T was more limited but still not satisfactory. The use of Omya Smartfill led again to a significantly lower MFR and matched the viscosity of unfilled PLA. Omya Smartfill does not require pre-drying or venting when compounding To test the effect of Calcium Carbonate on PLA properties, a 300mm working width laboratory casting line was used to make 800 µm PLA sheets with different Calcium Carbonate loadings. Fig 1 and Fig 2 show the same typical property changes Calcium Carbonate provides in PLA as expected with Calcium Carbonate addition in conventional thermoplastic polymers. Yield strength decreases, and stiffness increases with increasing Calcium Carbonate concentration. After sheet production, part of it was cut into small pieces to check the extent of degradation. This was done after the second heat history through MFR measurement (Fig 3). The results clearly show that Omya Smartfill does not cause additional PLA degradation, whereas Omyacarb 1T causes heavy degradation, which can make polymer processing difficult. In many polymers, the elongation at break is reduced due to the addition of mineral additives. Surprisingly Omya Smartfill added to PLA boosts the ultimate elongation. Fig 4 shows a strong increase in elongation at break achieved when adding Omya Smartfill with a maximum at around 20 % addition but even at 40 % addition elongation is far higher than for virgin PLA. This proves that Omya Smartfill increases stiffness and elasticity simultaneously and allows a processor to achieve high filler levels with superior mechanical properties. This effect can be seen also when adding Omyacarb 1T but to a much less extent, which could be related to degradation. Similar injection molding tests show comparable improvements and an increased impact strength on top, but there are additional benefits that contribute to overall cost savings when using 40 % Omya Smartfill, including: • 12 % lower specific heat capacity • 78 % higher thermal conductivity • 60 % higher thermal diffusivity • 89 % opacity at 30 % filler level without the use of titanium dioxide 26 bioplastics MAGAZINE [06/18] Vol. 13

By: 4500 4000 3500 3000 2500 2000 1500 1000 500 0 1000 500 0 100% PLA 10% Omya Smartfill 20% Omya Smartfill 40% Omya Smartfill 20% Omyacarb 1T Matthias Welker, Michael Knerr, Karsten 100% Schulz PLA 10% Omya Smartfill Omya International AG 20% Omya Smartfill 40% Omya Smartfill Oftringen, Switzerland 20% Omyacarb 1T Physical properties help to increase productivity. When 30 using Omya Smartfill in thermoforming or injection 20 molding, less energy is needed for heating and cooling and 10 lower cycle times can be achieved. Elongation at Break in MD [%] 80 70 60 50 40 80 70 60 50 40 30 20 10 0 100 90 80 70 60 100 50 40 90 30 80 20 70 10 60 50 0 Tensile Strength at Yield in MD [N/mm 2 ] Tensile Strength at Yield in MD [N/mm 2 ] 10 0 100% PLA 10% Omya Smartfill 20% Omya Smartfill 40% Omya Smartfill 20% Omyacarb 1T 0 100 100% PLA 10% Omya Smartfill Omya Smartfill is always the right choice when conventional Tensile Modulus MD [N/mm 2 ] 90 20% Omya Smartfill 40% Omya Smartfill Calcium Carbonate causes 80polymer degradation due to 5000 20% Omyacarb 1T hydrolysis. It is EU 10/201170 and FDA approved for food 4500 contact, it meets composting 60requirements and has passed 4000 50 3500 the ecotoxicity test. The material Elongation is supplied at Break as a powder in MD [%] 40 3000 Tensile Modulus MD [N/mm 2 ] and needs to be 100 pre-dispersed in a compound before being 30 2500 5000 used on conventional 90 single 20 screw extrusion lines. 2000 4500 80 10 1500 4000 Omya recently 70 received an 0 Innovator Award from the 1000 3500 Sustainable Packaging 60 Coalition (SPC) 100% as PLA a member 10% Omya 3000 500 Smartfill of PepsiCo’s Supply 50 Chain Partnership to 20% deliver Omya Smartfill a new 40% Omya 2500 Smartfill 0 40 20% Omyacarb 1T 2000 100% PLA 10% Omya Smartfill biobased film package to market. The outcome of a 30 1500 20% Omya Smartfill 40% Omya Smartfill Partnership Innovator Award was one of a select few entries 70 20% Omyacarb 1T 20 1000 chosen for advancing 10 the state of sustainable packaging. 500 60 Fig 2 NatureWorks, Danimer 0 Scientific, Berry Global, Johnson- 0 50 Bryce and PepsiCo also received 100% an PLA award. 10% Omya Smartfill 100% PLA 10% Omya 80 Smartfill www.omya.com 20% Omya Smartfill 40% Omya Smartfill 40 20% Omya Smartfill 40% Omya Smartfill 20% Omyacarb 1T 70 20% Omyacarb 1T 30 MFR @ 210C/2.16kg [g/10min] 60 70 20 50 Table 1: Moisture adsorption of common calcium carbonate grades and Omya Smartfill 55 - OM (mg/g, upon relative humidity change from 10% rH to 85 % rH at 23 °C) Calcium Carbonate Conventional un-treated Conventional treated Omya Smartfill 55-OM Moisture Adsorption 1580 ppm 750 ppm 390 ppm Table 2: MFR (210°C/ 2.16kg [g/10min]) (without degassing) MFR 100% PLA Ingeo 2003D 6 60% PLA + 40% Omyacarb 1T 49 60% PLA + 40% Omya Smartfill 5 Table 3: MFR (210°C/ 2.16kg [g/10min]) (with degassing) MFR 100% PLA Ingeo 2003D 6 60% PLA + 40% Omyacarb 1T 25 60% PLA + 40% Omya Smartfill 6 60 50 40 30 20 10 0 40 30 20 10 0 Fig 1 MFR @ 210C/2.16kg [g/10min] 40 80 30 70 Tensile Strength at Y 100% PLA 20 60 10% Omya Smartfill 20% Omya Smartfill 40% Omya Smartfill 10 20% Omyacarb 1T 50 40 0 30 100% PLA 20% Omya Smartfill 20 20% Omyacarb 1T 10 100% PLA 10% Omya Smartfill 20% Omya Smartfill 40% Omya 0Smartfill 20% Omyacarb 1T Elongation at Break in MD [%] Fig 3: MFR after sheet production Elongation at Break in MD [%] 100% PLA 10% Omya Smartfill 20% Omya Smartfill 40% Omya Smartfill 20% Omyacarb 1T 100% PLA 10% Omya Smartfill 20% Omya Smartfill 40% Omya Smartfill 20% Omyacarb 1T Fig 4: Impact of calcium carbonate to elasticity Materials Tensile Strength at Y 70 60 50 100% PLA 20% Omya Smartfill 20% Omyacarb 1T MFR @ MFR 40 70 30 60 20 50 10 40 0 bioplastics MAGAZINE 30 [06/18] Vol. 13 27 100% P

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