Biaxial orientation processes are commonly used to enhance the performance of polymeric materials. The development of molecular orientation during biaxial forming processes enables to produce materials that can be used in demanding structural applications or with enhanced optical or barrier properties. In these processes, deformation of a sheet or film takes place in both machine (MD) and transverse (TD) directions in the semi-solid state. Typical processes include the double-bubble, thermoforming and tenter frame processes, which are very widespread especially in the packaging industry. Poly(lactic acid) (PLA) is one of the biodegradable polymer available from renewable resources that has received a lot of attention recently, especially for food packaging applications. Adding starch to PLA also enables to reduce cost and maintain biodegradability. However, in its dry native form, starch acts as a filler and increases the inherent brittleness of PLA. In order to favor the ductility of the blends, starch can be plasticized using water and glycerol to form an immiscible polymer blend in which the thermoplasticstarch (TPS) is the dispersed phase. Processability using conventional polymer processing equipment is enhanced and better-quality morphologies can be obtained.
 M IHAI , M., H UNEAULT , M. A., F AVIS , B. D., L I , H., Extrusion foaming of semi-crystalline PLA and PLA/thermoplasticstarch blends, Macromolecular bioscience, Vol. 7, 2007, p. 907.
 N IKITINE , C., R ODIER , E., S AUCEAU , M., L ETOURNEAU , J., F AGES , J., Controlling the Structure of a Porous Polymer by Coupling Supercritical CO2 and Single Screw Extrusion Process, Journal of Applied
Low-density open-cell foams were obtained by extrusion process from polylactic acid (PLA) and from blends of PLA with thermoplasticstarch (TPS) using CO 2 as blowing agent. Two unexpected features were found. First, a 2D
cavitation process in the fractured cell walls was unveiled. Elliptical cavities with dimensions in the 100-300 nm range were aligned perpendicular to large cell cracks clearly exhibiting 2D crazing prior to macroscopic cell rupture. Secondly, a significant crystallization rate increase associated with the CO 2 foaming of PLA was discovered. While the
D-lactic acid monomer. The two different thermoplasticstarch materials, prepared through reactive extrusion processing, contain 36% glycerol (TPS36-1) and 24% glycerol + 12% sorbitol (TPS36-2) as plasticizers . PLA/TPS were blended by extrusion using only the aPLA and TPS36-2 at a 50/50% weight ratio in order to screen the composite blend behaviour. The wood fibers, yellow birch (HW) and black spruce (SW), were supplied by FPInnovations, Wood Products division in Quebec, Canada. They were obtained from wood chips via a thermo-mechanical refining process usually used to produce MDF wood fibres.
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Processing and Properties of Biaxially Oriented Poly(lactic acid)/ThermoplasticStarch Blends
2.2 Blend Compounding
The PLA and starch were blended using a twin-screw extrusion process as described by Rodriguez-Gonzalez et al. (2003). The blends were made on a Leistritz 34 mm co-rotating twin-screw extruder with an L/D ratio of 42. The first half of the extruder was used to prepare the thermoplasticstarch (TPS). The extru- der was fed with a starch suspension in a water/glycerol mix- ture. The initial starch content was 50 wt.% and the water/gly- cerol ratio adjusted to obtain the desired glycerol content in the final TPS. The starch was gelatinized under pressure in the first mixing zone at 130 &C. The water was then removed from the thermoplasticstarch by vacuum just before mid-extruder to obtain a TPS with minimum residual water. The glycerol content in the TPS was 36 wt.% on a dry basis. The PLA (mod- ified or not) was incorporated in the molten form at mid-extru- der through a single-screw extruder side-feed. The PLA and TPS underwent mixing in a zone maintained at 180 &C. The resulting PLA/TPS blend was extruded through a strand die, water-cooled and pelletized. Blends containing 27, 42 and 60 wt.% TPS were studied. For interface modified samples, the PLA was grafted using 2 wt.% maleic anhydride and 0.25 wt.% peroxide initiator. These latter two components were introduced along with the PLA in the side-feed single- screw extruder. The details of this procedure are described else- where (Huneault and Li, 2007). It is believed that the maleic anhydride grafted onto the PLA is reacting with the hydroxyl group of the starch. Prior to any compounding or further pro-
In this part of the work, all formulations of TPS—i.e. glycerol-TPS, sorbitol-TPS, diglycerol-TPS and polyglycerol-TPS—were subjected to two preliminary tests, examining moisture uptake level and temperature stability. Polyglycerol-TPS showed the least moisture uptake (15%), compared to glycerol-TPS (40%) at 25˚C and 80% humidity. So the above-mentioned humidity-induced fluctuations in the mechanical properties are less pronounced for polyglycerol-TPS, followed by diglycerol-TPS and sorbitol-TPS. The heat stability measurements also revealed new potential applications for polyglycerol-TPS. It was shown that the 5% plasticizer weight loss temperature for glycerol-TPS is 156˚C, which, considering the high processing temperature of the majority of commodity plastics (>150˚C), it is expected that high evaporation rates of the plasticizers would be observed during the process. Interestingly, it was found that the 5% plasticizer weight loss temperatures for sorbitol-TPS, polyglycerol-TPS and diglycerol-TPS are 235˚C, 225˚C and 203˚C, respectively, which, combined with their less hygroscopic nature, opens a wide range of applications for thermoplasticstarch. In order to evaluate the performance of the new plasticizers in the TPS blends, blends of HDPE/TPS:80/20wt% were prepared through a patented process in the laboratory. Scanning electron microscopy results, demonstrated that despite the high viscosity of the new plasticizers, the droplet size of the TPS in PE matrix falls into the same region as glycerol-TPS. A copolymer (PE-g-Maleic Anhydride) was further added to the blends in various compositions. The emulsification curves show that the volume average droplet size (d v ) and
Morphology control is considered as one of the key factors to achieve the desired final material properties. The morphology of polymer blends greatly depends on the rheology of the components used in the blends. The second paper, ―Morphology Development and Interfacial Interactions in Polycaprolactone/ThermoplasticStarch Blends‖, presents an approach to the investigation of the morphology, thermal and mechanical properties of blends of polycaprolactone (PCL) and thermoplasticstarch (TPS) with high glycerol content. Dynamic rheological measurements were carried out on a dynamic stress rheometer with frequencies from 0.1 to 500 rad/s. The morphology of the extruded PCL/TPS strands was obtained using scanning electron microscopy and a semi-automatic method of image analysis was applied to quantify the average size of the dispersed phase. The morphology of PCL/TPS36 blends demonstrates the features of a highly interacting system, and the tensile mechanical properties demonstrate exceptional ductility at very high levels of thermoplasticstarch without any added interfacial modifier. In addition, the effects of viscosity ratio of dispersed phase/matrix on morphology of PCL/TPS36 were discussed. Dynamic mechanical analysis confirms the region of dual-phase continuity and also strongly indicates a specific interaction between PCL and TPS. FTIR results show the presence of a hydrogen bonding interaction between the carbonyl groups of PCL and the hydroxyl groups on starch. It is likely that the high plasticizer concentrations used here increase the mobility of the starch chains and thus promote a high level of specific interactions between the PCL and starch. Mechanical properties display extremely high elongations at break, even at high TPS concentrations, typical of those observed for highly compatibilized immiscible polymer blends.
2. INRA, LCA (Laboratoire de Chimie Agro-industrielle)
3. Vegeplast, Parc des Pyrénées, 2 rue de Troumouse, 65420 IBOS, France -*email@example.com
During the last decade, thermoplasticstarch (TPS) has been studied more and more, alone and in blends. One key property of TPS is its viscosity. A lab-scale conical twin-screw extruder has been used to process polymers or blends of polymers at a small scale (7 cm 3 ), and to measure their viscosity by pressure loss in a backflow channel. TPS has been tested at different temperatures (100-180°C) and for a 100-900s -1 shear rate range. One surprising result is the viscosity evolution of starch/glycerol blends (supposed to have become TPS before the rheology measurements) with temperature. An increase is observed between 120 and 140°C and then it decreases between 140 and 160°C. Therefore plasticization may happen only from 140°C. Blends of TPS with PLA and with different additives have also been studied. The additives are introduced in a second time, ten minutes after the TPS/PLA blend recirculation. Their influence on the blend viscosity is instantaneous. A viscosity increase after the additive introduction can be a clue for an improvement of the blend compatibilisation, as observed with CMC. Thanks to this micro-compounder, viscosity and behaviour of polymers can be evaluated easily even for TPS which needs shear to flow. Moreover, the solidified sample collected in the backflow channel at the end of the experiment can be used to test different properties like mechanical or thermal (DMTA, DSC) ones. Using this kind of lab-scale extruder represents then a good opportunity for preview screening studies.
2 Industrial Materials Institute, National Research Council, 75 de Mortagne
Boucherville, Que´bec, Canada, J4B 6Y4
ABSTRACT: This study investigates the fabrication of extruded foams from polystyrene/thermoplasticstarch (PS/TPS) blends. A specially designed twin- screw extrusion process is used for starch gelatinization, PS incorporation, polymer mixing, and blowing agent incorporation. In-line rheometry is used to monitor the viscosity of the TPS/PS blends and to evaluate the plasticizing effect of 1,1,1,2 tetrafluoroethane (HFC-134a) used as blowing agent. Differential scanning calorimetry, scanning electron microscopy, density measurement, and picnometry are used to evaluate the thermal properties, the blend morphology, and the foam cell structure. Glycerol content in the TPS phase and the TPS content in the overall blend have a strong effect on the blend viscosity and, in turn, on the ability to foam the material. The foams blown with the hydro- fluorocarbone alone have large open-cell content and their density cannot be reduced below 170 kg/m 3 . The addition of a small amount of ethanol however results in three-fold reductions in density and much better foam cell homogeneity. KEY WORDS: thermoplasticstarch, polystyrene, foam extrusion.
study, however, the twin-screw extrusion process had to be
adapted in order to incorporate and dissolve the blowing agent into the polymer in the second half of the extruder. A sketch of the screw configuration is presented in Figure 2. The extruder was a Leistritz 34 mm co-rotating twin-screw extruder. It was operated at a screw rotation speed of 150 rpm and for a total flow rate of 10 kg h 1 . A suspension made from starch/glycerol/water was fed into extruder segment 0 at a controlled rate using a volumetric slurry pump. Precise feed rate values were obtained by monitoring the loss-in-weight on the starch suspension reservoir. The first two extruder segments after feeding were used to heat and gelatinize the starch. Section 3 and 4, operated at 110 8C, were used to remove the water by atmospheric and then by vacuum vapori- zation, respectively, to obtain a water-free glycerol-plasticized starch. Molten PLA or PLA mixed with PLA-g-MA was pumped into the twin-screw segment 5 using a 25 mm single-screw extruder. The feed rate of the PLA/PLA-g-MA was controlled using a loss- in-weight feeder. The polymer and plasticized starch were mixed together in segment 6 and 7. The CO 2 was pumped into barrel
from a mixed suspension of hemp cellulose nanocrystals (HCNs) and thermoplasticstarch, or plasticized starch (PS), by the casting and evaporating method. The mor- phology, thermal behavior, mechanical properties, and water sensitivity of the ﬁlms were investigated by means of scanning electron microscopy, wide-angle X-ray diffrac- tion, differential scanning calorimetry, tensile testing, con- tact angle measurements, and water absorption. The re- sults indicate that the cellulose nanocrystals dispersed in the PS matrix homogeneously and resulted in an increase in the glass-transition temperature ascribed to the fact that the ﬂexibility of the starch molecular chains in the starch- rich phase was reduced because of the strong intermolecu-
1) ICMR, UMR CNRS 7312, 2)FARE, UMR INRA, Université de Reims Champagne Ardenne,
3) INRA UMR 1318 Institut JPB - AgroParisTech Versailles, 4) DTPCIM - Ecole des Mines de Douai
ThermoplasticStarch (TPS) represents ca 80% of the biopolymer market, however, unlike petroleum based polymers, TPS is still manufactured by traditional methods of extrusion and injection molding.
Starch is particularly a good candidate for the manufacturing of environmentally friendly materials, especially as a replacement for synthetic films in food packaging. Starch is totally biodegradable and of low cost. Starch granules, which consist of amylose and amylopectin, are semi-crystalline. Pure starch films are brittle because of the strong interactions in the macromolecular chains. Starch-based films are often prepared by dilute solution casting. Although commercially viable, this technique has many drawbacks and melt extrusion can be an interesting alternative. Starch can be gelatinized to form thermoplasticstarch (TPS) and produce flexible films. The gelatinization is carried out in an extruder by applying shear and heat in presence of plasticizers such as water and glycerol. The resulting TPS material can then be processed into sheets or films. Potential applications for TPS films include food packaging, where barrier properties are critical, and water-soluble pouches or coatings, for which the solubility behavior is important. The addition of the plasticizers and other additives such as salts and surfactants will greatly affect the final properties of the films. Several studies have addressed the film forming capacity of starch by using solution casting [1-4]. However, there are few studies on the production of starch-based films by melt extrusion and the impact of processing conditions and incorporation of additives on the final properties of the films [5-8].
phenomenon is typical of thermoplasticstarch recrystallization ob- served in presence of glycerol (vanSoest & Vliegenthart, 1997).
The di ﬀractograms obtained after a storage time ranging from one week to one year showed a progressive recrystallization in B-type crystallinity. (As an example of the diﬀractogramms obtained for cho- line acetate plasticized starch are presented as supplementary data (Supplementary Figure B)) For all plasticized starches the crystallinity did not evolve signiﬁcantly after 4 month. Table 1 shows the calculated B-type crystallinity levels after one year of storage. The values observed in presence of glycerol, [Chol][Lac] and [Chol][Cl] are similar, while again a diﬀerent behavior is observed in presence of [Chol][Ace], with a signiﬁcantly stronger B-type recrystallization. However, the occur- rence of B-type recrystallization for the three choline based ionic plasticizers is consistent with the results previously reported for starch plasticized by choline chloride based DES (Choline Cl/glycerol and Choline Cl/urea mixtures) after similar processing conditions (Leroy, Decaen et al., 2012).
It should be emphasized that although the flocculation performance of CMS in terms of settling rate is lower and the required dosage is higher than the commercial flocculants, the cost of CMS is much lower too, thus making CMS as potentially economically competitive flocculants without secondary pollution. Nevertheless, in this work we explored the possibility of applying the natural product based flocculants to treat oil sand tailings. The lab-scale tests demonstrated the feasibility. However, it is expected that there will be challenges for the large-scale application of CMS in oil sand tailing treatment. Based on our test results, it can be foreseen that employing or synthesizing new types of natural polymers with superior water solubility, high molecular weight, and great chain linearity to replace the potato starch could be the effective strategy for improving the settling rate of tailings.
2. Experimental Procedures 2.1. Materials
Four continuous fibre thermoplastic composite materials were investigated in this study. These materials consist of glass fibre/polypropylene (GF/PP), glass fibre/polyamide 6 (GF/PA6), carbon fibre/polyamide 6 (CF/PA6) and carbon fibre/polyamide 66 (CF/PA66) composites. The materials considered in this study were all in the form of pre-impregnated thermoplastic unidirectional tapes. Table 1 shows the fibre content, density, thickness and the melting temperature of these composites, as determined by differential scanning calorimetry (DSC).
Since their appearance in the 1960s, thermoplastic elastomers (TPEs) are being increasingly considered for a range of applications including automotive, medical equipment and aeronautics. In particular, linear segmented polyurethane elastomers (TPUs) are potential candidates for replacing thermoset elastomers, as they present similar mechanical properties such as low modulus or elasticity behaviour. Conventional thermoplastic processes such as injection moulding or extrusion are used for these materials. The overall processing of TPEs is thus simpler compared to thermoset elastomers. They also do not require curing systems or reinforcing agents. This point is of importance for industrial use, as regulations are becoming more restrictive towards the use of hazardous chemicals in industrial processes. We can for example cite the REACH regulation concerning the European Union, adopted to improve the protection of human health and environment. In this