Thermoplastic Starch Materials Research Articles

Characterization of Thermoplastic Starch Plasticized with Ternary Urea-Polyols Deep Eutectic Solvent with Two Selected Fillers: Microcrystalline Cellulose and Montmorillonite

The aim of the study was to prepare and characterize composite materials based on thermoplastic starch (TPS)/deep eutectic solvent (DES). Potato starch was plasticized with ternary DES: urea:glycerol:sorbitol and modified with the selected fillers: microcrystalline cellulose and sodium montmorillonite. Films were prepared via twin-screw extrusion and thermocompression of the extrudates. Then, the physicochemical properties of the TPS films were examined. The ternary DES effectively plasticized the polysaccharide leading to a highly amorphous structure of the TPS (confirmed via mechanical tests, DMTA and XRD analyses). An investigation of the behavior in water (swelling and dissolution degree) and water vapor transmission rate of the films was determined. The introduction of the two types of fillers resulted in higher tensile strength and better barrier properties of the composite TPS films. However, montmorillonite addition exhibited a higher impact than microcrystalline cellulose. Moreover, a cone calorimetry analysis of the TPS materials revealed that they showed better fire-retardant properties than TPS plasticized with a conventional plasticizer (glycerol).

Biodegradable composites of starch/polyvinyl alcohol/soybean hull (Glycine max L.) produced by thermoplastic injection

AbstractSoybean hull is an agro‐industrial residue produced abundantly both in Brazil and worldwide. It is generated during the dehulling of the grains for oil production. This work aimed to develop materials using low‐cost, abundant, and biodegradable raw materials, as soybean hull, corn starch, polyvinyl alcohol (PVA), and glycerol. Five formulations of thermoplastic starch (TPS) were produced containing between 4% and 19% of ground soybean hull and another five formulations of the same composition but with 6% PVA added. The materials were extruded and injected to produce specimens. They were analyzed by FTIR‐ATR, mechanical tests, mass loss in water, and dimensional variations. The addition of hull to the TPS did not affect the processability of the materials, and the PVA improved the processability. Hull concentration from 8% to 15% increased the tensile strength of the materials, and the PVA reduced them. Soybean hull provided greater dimensional stability to the specimens, especially with PVA and with the highest hull contents (15% and 19%).Content of soy hulls between 8% and 15% acted as a structural reinforcer of TPS materials, forming a composite, as it increased the tensile strength, reduced the elongation, increased the stiffness, and improved the dimensional stability of the materials.

The modification of properties of thermoplastic starch materials: Combining potato starch with natural rubber and epoxidized natural rubber

In this paper, natural rubber (NR) and epoxidized natural rubber (ENR) are used as potential modifiers of thermoplastic potato starch (TPS). The mechanical and thermal properties, water absorption, and biodegradability were tested. The results show that ENR can be used as a compatibilizer for NR and TPS. As the rubber content (mainly ENR content) increases, the tensile strength of the material decreases and the elongation at break increases. With increasing ENR content, the changes in various properties of the material are unexpected. The development of the ternary blend enables a modified material to have an expected good mechanical property. Low rubber content blends exhibit high biodegradability. The developed material can be processed via compression molding. TPS, unvucanized NR, and ENR are all-natural green materials, so this provides new ideas for the development of environmentally friendly materials.

Sodium Hexametaphosphate‐Modified Thermoplastic Starch Materials Prepared with the Assistance of Supercritical CO2

AbstractThis paper describes sodium hexametaphosphate (SHMP)‐modified thermoplastic starch (TPS) resins (scCO2TPS100SHMPx) gelatinized and/or modified with the aid of supercritical carbon dioxide (scCO2). TPS and scCO2TPS100SHMPx exhibit considerably higher melt flow rates, moisture resistance, and initial and retention tensile strength values than TPS and TPS100SHMPx prepared using conventional atmospheric pressure. Only Vh‐type crystals are found in conditioned scCO2TPS100SHMPx, which show significantly lower melting temperatures (≈19 °C) than the corresponding conditioned TPS100SHMPx. Relative to TPS100SHMPx, conditioned scCO2TPS100SHMPx show a weaker hydrogen bonding network among the hydroxyl groups in the amylopectin chains and considerably less retrogradation. The loosely hydrogen‐bonded hydroxyl groups found in conditioned scCO2TPS100SHMPx can be replaced with stronger hydrogen bonds involving the phosphate groups of SHMP through the proper modification of scCO2TPS100SHMPx.

Tapioca/polyvinyl alcohol thermoplastic starch materials processed with the aid of supercritical CO2

Abstract This paper represents the first report of polyvinyl alcohol (PVA) modified TPS resins (scCO2TPSxPVA05y), gelatinized and/or modified with the aid of supercritical carbon dioxide (scCO2). The melt flow rate, initial and retention values of tensile strength (σf) of scCO2TPSxPVA05y prepared with the aid of both scCO2 and PVA05 were considerably higher than those of the corresponding scCO2TPS prepared using scCO2 fluid and/or TPSxPVA05y materials prepared in the conventional way. The moisture contents of conditioned scCO2TPSxPVA05y were considerably lower than those of the corresponding scCO2TPS and TPSxPVA05y aged for the same amounts of time. Conditioned scCO2TPSxPVA05y exhibited only Vh-type crystals with melting temperatures ∼ 40 °C and ∼ 20 °C lower than those of corresponding conditioned TPS and TPSxPVA05y, respectively. In comparison to TPS and TPSxPVA05y, more dissociated amylopectin chains with loosely hydrogen-bonded −OH groups and significantly less retrogradation was obtained for conditioned scCO2TPS and scCO2TPSxPVA05y, respectively.

Effect of fiber loading on properties of thermoplastic sago starch/kenaf core fiber biocomposites

Growing attention has been paid to the innovation of ecological products, prompted by rising environmental concerns. As a natural polymer, thermoplastic sago starch has been regarded as an alternative material to petroleum-based plastic owing to its availability, cost, and biodegradability. In order to produce thermoplastic starch materials with enhanced structural and functional stability during use, kenaf fibers were incorporated as the reinforcing filler. In this work, thermoplastic sago starch (TPSS)/kenaf core fiber (KF) biocomposites were prepared at different fiber loadings (0 to 35 wt.%), and the effects of fiber loading were analyzed by mechanical tests, TGA, FTIR, SEM, and water absorption behavior. The tensile analysis showed a linear increase in strength and modulus upon increasing fiber content until it reached an optimum at 30 wt.% fiber loading. The thermal stability of biocomposites was improved slightly by the incorporation of kenaf fibers into TPSS matrices. FTIR results indicated a change in the functional group of the biocomposites. Moreover, the interfacial adhesion properties of biocomposites were evident from morphological studies of tensile fracture surfaces. It is interesting to note that water absorbed by the biocomposites was reduced by the addition of fiber, and it seems that the hydrophilic character was decreased especially for the glycerol-plasticized sample. The results obtained clearly illustrate the potential use of these fiber and biopolymers to establish their suitability as alternative biocomposite materials.

Antibacterial thermoplastic starch-chitosan based materials prepared by melt-mixing

Antibacterial thermoplastic starch-chitosan based materials were successfully prepared by melt-mixing. The effect of chitosan modification (quaternization and grafting of long carbon chains) on the properties of the materials was also studied. All the ensuing materials were characterized in terms of thermal stability, crystalline structure, mechanical performance, and antibacterial activity. The incorporation of chitosan and its derivatives into the thermoplastic starch matrices resulted in an increment in tensile strengths (up to 85%); however for higher chitosan contents (5 and 7.5 wt.%), a decrease on the Young’s modulus (around 50%) was observed, together with an increment in the elongation at break, which can be attributed to the prevention of the retrogradation process. Finally, the thermoplastic starch materials incorporated with 7.5 wt% of the unmodified chitosan and of the water-soluble chitosan derivative had partial (about 20% reduction of CFU) and total bactericidal effect against S. aureus.

Effect of amphiphilic molecules on characteristics and tensile properties of thermoplastic starch and its blends with poly(lactic acid)

Three different types of amphiphilic molecules — Tween 60, linoleic acid, and zein were used as additives for the production of thermoplastic starch (TPS). The addition of those amphiphiles resulted in: (i) improved plasticization and processability, (ii) enhanced extensibility, (iii) increased crystallinity, and (iv) decreased stiffness, strength and rigidity of the TPS materials. Zein facilitated more effective plasticization, melting and processability of TPS material than did linoleic acid and Tween 60, respectively. However, Tween 60 allowed greater reduction of T g and produced softer TPS material than did linoleic acid and zein, respectively. Binary blends of those TPS materials and poly(lactic acid) (PLA) were also fabricated by varying PLA content, i.e. 30, 50 and 70% (w/w). The melt flow index, tensile strength and elastic modulus of the TPF-PLA blends increased significantly with increasing PLA content. In addition, amphiphiles facilitated processability, flowability and extensibility of the blends. Linoleic acid was a more effective additive to enhance flowability of the TPS–PLA blends than were Tween 60 and zein, respectively.

The enzymatic hydrolysis of starch-based PVOH and polyol plasticised blends

Thermoplastic starch (TPS) materials present several advantages to the plastic industry and when blended with other materials they can exhibit improved mechanical and moisture sensitivity properties compared to pure TPS materials. However, the biodegradability of these blends, through such processes as enzymatic degradation, needs to be characterised to ensure the beneficial properties of TPS are not compromised. The aims of the study were to investigate the effect of varying polyvinyl alcohol (PVOH) content and polyol type within the TPS blends on the rate and extent of starch enzymatic hydrolysis using enzymes α-amylase and amyloglucosidase. The results of this study have revealed that TPS:PVOH blends with a PVOH content at 50 wt% exhibited a significantly reduced rate and extent of starch hydrolysis. The results suggest that this may have been attributed to interactions between starch and PVOH that further prevented enzymatic attack on the remaining starch phases within the blend. The extent of starch hydrolysis was not significantly affected by polyol type, however, the rate of starch hydrolysis from the maltitol blend was significantly reduced compared to sorbitol and glycerol substrates.

Film blowing of thermoplastic starch

Thermoplastic starch materials are often based on a combination of starch, glycerol and water. In the present study, two potato starch grades were employed; a native (natural) grade and an oxidised and hydroxypropylated grade of the native material, in order to produce the thermoplastic material. The primary aim of the study was to identify possible routes for film blowing thermoplastic starch on a laboratory scale by a suitable choice of processing conditions, amount of glycerol and moisture content. With an appropriate combination of these parameters, the thermoplastic material based on the modified starch could be film blown in a satisfactory manner. Film blowing of material based on the natural starch was significantly more difficult. The difficulties encountered were mainly related to a sticky surface of the film, insufficient tenacity and foaming. The processing window for thermoplastic starch (related to film blowing) is briefly outlined and discussed.

On the Stress-Strain Behavior of Thermoplastic Starch Melts

Different grades of starch, glycerol, and water were blended in order to produce a series of thermoplastic starch materials. The starch grades used included native potato starch and modified grades of native potato starch, high amylose potato starch, and amylopectin potato starch. The modification of the latter three grades involved hydroxypropylation and oxidation. The main focus of the study was on the stress-strain properties or the drawability of the thermoplastic starch melts at 120° or 140°C. At these temperatures, the ultimate strain of the starch materials was found to be significantly lower than that of a high-density polyethylene reference at 180°C. In general, the strain at break of the melts based on the native potato starch and the modified native potato starch tended to increase when increasing the glycerol content (and the corresponding amount of water) but decreased as the melt temperature was increased from 120° to 140°C. The chemical modification of the native potato starch appeared to promote the drawability of the melt.

Quaternary starch based blends: Influence of a fourth component addition to the starch/water/glycerol system

This paper deals with the effects of the addition of a fourth component to the starch glycerol/water/system used in thermoplastic starch materials on the basis of starch sorption site availability. These sites can sorbed both water and glycerol depending on the glycerol content and the chosen relative humidity. Starch sorption sites are saturated by specific glycerol+water concentrations, which defined the starch saturation point. The addition of a fourth component before, near or after this starch saturation point is a potentially interesting concept because of its effect on the mechanical properties of the whole system (quaternary system). This was illustrated with various types of fourth components introduced at low concentrations. The addition of maltose led to an efficient coplasticizing effect only after the saturation point. The addition of a polar polymer led to a strain increase (at break) before and at the saturation point, and to a strain decrease after the saturation point. The addition of fillers at the saturation point led to an unattempted plasticizing effect.

The role of plasticization in starch granule assembly.

There is a growing interest in the nonfood usage of starch-based products. This interest is predominantly motivated by the ability to produce thermoplastic materials, known as thermoplastic starch (TPS), which can be manufactured using technology already developed for the production of synthetic plastics yet which are fully biodegradable. With the strength and flexibility of TPS materials being highly dependent upon the presence of nonaqueous plasticizing solvents, the nature of the interaction between starch and plasticizer is of obvious interest. As well as interest in the industrial applications of starch, the general nature of plasticization and structure formation within native starch granules is of fundamental interest. This paper presents results from a small and wide angle scattering and calorimetric investigation of model starch-plasticizer systems. Issues relevant to TPS production are addressed, and a model of lamellar assembly within starch granules facilitated by the plasticizing effect of low molecular weight solvents is proposed.

Rheological Characterization of Thermoplastic Starch Materials

The rheological characterization of thermoplastic starches (TPS) by using a capillary rheometer includes the research of their flow properties depending on compounding parameters, on types and contents of incorporated additives, as well as on melt temperatures. Based on extensive experimental studies, the viscosity functions of glycerol de-structurized TPS types can be described analytically by the definition of a new combined shift factor, which considers the influence of both melt temperature and additive amount. Wall-slip effects due to specific TPS formulation; were quantified by the application of a modified Mooney procedure.

Structure and properties of compression-molded thermoplastic starch materials from normal and high-amylose maize starches

The structural and mechanical properties of compression-molded normal and high-amylose maize starches were studied as a function of processing water content and ageing time. Rubbery thermoplastic starches were produced by compression molding of four maize starches with differences in amylose content and amylopectin structure. Glycerol (30% on the basis of dry starch) and water (between 10 and 35% on the basis of total mass) were used as plasticizers. After processing, the amorphous thermoplastic starch materials crystallized during ageing. The semicrystalline materials contained both E-type and V-type, as well as B-type crystallinity. The properties of the thermoplastic starch materials are dependent on water content during processing, starch source, and ageing time. The normal maize starch materials are highly flexible with elongations between 56 and 104%. The elongations of the high-amylose maize starch materials were between 5–35%. The tensile stress and E-modulus of the normal maize starch materials were in the range of 3.9–6.7 and 27–131 MPa, respectively. The tensile stress and E-modulus of the high-amylose maize starch materials increased from approximately 0.5 to 23 and 5 to 700 MPa, respectively, with increasing water content during processing from 10 to 35%. The differences in mechanical properties of the normal and high-amylose materials were explained by differences in the structure of the amylose and amylopectin structure. It was concluded that both lead to differences in the starch network. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 631–644, 1997

The influence of starch molecular mass on the properties of extruded thermoplastic starch

The mechanical properties of a low and a high molecular mass thermoplastic starch (TPS) were monitored at water contents in the range of 5–30% (w/w). The granular starches were plasticized by extrusion processing with glycerol and water. The low molecular mass starch was prepared by partial acid hydrolysis of potato starch. The extruded TPS materials were stored at 60% relative humidity for 12 months to level out differences in starch structure due to retrogradation. The water content was then varied by an additional storage period at various humidities. The average molecular masses of the TPS materials, composed of native starch or of hydrolysed starch, were 37 000 and 1900 kg mol −1, respectively. The apparent amylose contents of the high and low molecular mass materials were 25% and 11%, respectively. Differences were observed in thermal properties and crystallinity between the two types of materials, as a function of water content but not as a function of molecular mass. The stress-strain properties of the materials were dependent on the water content. The materials showed a viscoelastic behaviour characteristic of a semicrystalline polymer. Materials containing less than 9% water were glassy with an elastic modulus between 400 and 1000 MPa. For the materials a transition from brittle to ductile behaviour occurred at a water content in the range of 9–10%, which is in accordance with the observed glass transition temperature at this water content. The rubbery materials, with a water content of 9–15%, were tough and an optimum in ultimate elongation was observed. Above a water content of 15% the materials became weak and soft and the strain at break decreased. No significant differences in brittle-to-ductile transition as a function of water content were observed between the low and high molecular mass TPS materials. In the rubbery state with 14% water, the elongations at break of the high and low molecular mass materials were 100–125% and 30–50%, respectively. The tearing energy of the materials showed a maximum at a water content of 9–10%. The energies at this maximum of the high and low molecular mass materials were 0.15 and 0.1 J mm −2, respectively. The lower strain and tearing energy of the low molecular mass materials in the rubbery state were attributed to the reduced amylose chain length as well as the molecular mass and the degree of branching of the amylopectin molecules. This resulted in a material with a less effective entangled starch matrix. The entanglements were described as a complex network of the linear amylose chains and the outer chains of the amylopectin molecules in which hydrogen bonding plays an important role.

Changes in the mechanical properties of thermoplastic potato starch in relation with changes in B-type crystallinity

The influence of crystallization on the stress-strain behaviour of thermoplastic potato starch has been monitored. Potato starch has been processed by extrusion with glycerol and water added as plasticizers. The thermoplastic starch consists of a molecular network of semicrystalline amylose and amylopectin with some granular fragments. A rapid increase in B-type crystallinity and a change in mechanical properties is observed within 2 weeks at 70 and 90% relative humidities. An increase in B-type crystallinity from 5 to 30% compared to native potato starch leads to an increased elastic modulus (from 10 to 70 MPa) and tensile stress (from 3 to 7 MPa) for thermoplastic starch materials with a water content of circa 15%. The elongation is decreased from 105 to 55%. For materials with more than 30% B-type crystallinity relative to native potato starch, a sharp decrease in elongation is observed and the materials form cracks. The effects are explained by an increase in physical cross-links by amylose and amylopectin intermolecular double helix formation and crystallization resulting in a reinforced network. A further intramolecular crystallization of the amorphous amylopectin reduces the intermolecular interactions of amylopectin and induces internal stress within the network of semicrystalline amylose and amylopectin. The increased internal stress at the highly crystalline amylopectin sites finally leads to cracking of the materials.