Injection Molded Articles Research Articles

Poly(lactic acid)/thermoplastic cassava starch blends filled with duckweed biomass

Duckweed (DW) is a highly small, free-floating aquatic plant. It grows and reproduces rapidly, comprises mainly protein and carbohydrate, and has substantial potential as a feedstock to produce bioplastics due to its renewability and having very little impact on the food chain. The aim of this work was to analyze the effect of DW biomass on the characteristics and properties of bio-based and biodegradable plastics based on a poly(lactic acid)/thermoplastic cassava starch (PLA/TPS) blend. Various amounts of DW biomass were compounded with PLA and TPS in a twin-screw extruder and then converted into dumbbell-shaped specimens using an injection molding machine. The obtained PLA/TPS blends filled with DW biomass exhibited a lower melt flow ability, higher moisture content, and increased surface hydrophilicity than the neat PLA/TPS blend. Incorporation of DW with low concentrations of 2.3 and 4.6 wt% increased the tensile strength, Young's modulus, and hardness of the PLA/TPS blend. Moisture and glycerol from DW and TPS played important roles in reducing the Tg, Tcc, Tm, and Td of PLA in the blends. The current work demonstrated that DW could be used as a biofiller for PLA/TPS blends, and the resulting PLA/TPS blends filled with DW biomass have potential in manufacturing injection-molded articles for sustainable, biodegradable, and short-term use.

Morphological characteristics and properties of TPS/PLA/cassava pulp biocomposites

The effect of cassava pulp (CP) on morphological, tensile, and thermal properties of a thermoplastic cassava starch (TPS)/poly (lactic acid) (PLA) blend was investigated. TPS/PLA/CP biocomposites were manufactured by melt extrusion and then converted into specimens using an injection molding. The weight fraction of PLA to TPS/CP was fixed at 40:60, whereas the final CP concentration in the composites was varied in the range of 4.4–22.1 wt%. CP could act as a reinforcement for TPS/PLA blend to enhance its tensile strength up to 354% and Young's modulus up to 722% when 22.1 wt% of CP was loaded and a nucleating agent for PLA as confirmed from the reduced Tcc. In addition, TPS/PLA/CP composites showed a discrete phase structure (i.e., droplets in matrix) when CP with lower concentration (i.e., 4.4 wt%, 8.8 wt%, and 13.3 wt%) was incorporated and a bicontinuous phase structure (i.e., co-continuous) when higher concentration of CP (i.e., 17.7 wt% and 22.1 wt%) was employed. The results suggest that TPS/PLA/CP biocomposites have potential to be used in the manufacturing of injection-molded articles, particularly when biodegradability and renewability of the material are required.

Injection-molded polyethylene/natural rubber blends

The present research aims to develop polyethylene/natural rubber (PE/NR) blends, with a weight proportion of PE:NR of 60:40, for injection-molded articles. Two types of PE, i.e. high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) were used. The blends were fabricated by melt processes and then converted into dumbbell-shaped specimens using an injection molding machine. The effect of NR on properties of PE was investigated. The blends showed lower melt flow ability than the corresponding PE. Although PE/NR blends exhibited lower tensile strength and Young’s modulus than PE, their elongation at break and impact strength tended to be higher. In addition, hardness and heat distortion temperature of PE decreased by blending with NR. The obtained PE/NR blends are thermoplastics, which can be further converted into product prototypes using injection molding process.

Enhancing mechanical performance of polylactide by tailoring crystal morphology and lamellae orientation with the aid of nucleating agent

The performance of semicrystalline polymers is significantly dependent on the crystal morphology and lamellae orientation. In this work, the crystal superstructure and mechanical properties of polylactide (PLA) with different amounts of nucleating agent (tetramethylene-dicarboxylic dibenzoyl-hydrazide, TMC-306) were investigated. It was found that TMC-306 can be dissolved in PLA melt and re-crystallize into fibrils upon cooling. These fibrils can serve as nucleation templates to induce the crystallization of PLA on their surface, resulting in a large enhancement in crystallization rate. More importantly, PLA lamellae can grow perpendicular to the long axis of TMC-306 fibrils, inducing the formation of shish-calabash, shish-kebab and needle-like structures, depending on the concentration of TMC-306 used. Taking advantage of shear flow experienced in injection molding, TMC-306 fibrils tend to align in PLA melt along the shear flow direction, inducing the formation of highly orientated PLA lamellae in injection-molded articles. In this way, a simultaneous improvement in impact toughness, tensile strength and elongation at break is achieved. This work provides a good example of using a fibrous nucleating agent as a template to tailor the crystal morphology and lamellae orientation, thus achieving greatly enhanced properties for PLA.

Role of Polymer in Weeding and Seeding Machinery in Agriculture Rice Mechanization

In agricultural farm machinery, polymers are widely used for many applications. In recent years many agricultural farm implements are adopting polymer based plastic parts like seed dill ferule roller, weeding equipment, star wheel of harvester, vegetable planter hopper, zero till drill flute, animal yoke, maize sheller, diary vessels etc as a step towards value engineering. By varying the synthetic blend component and its miscibility with starch, the morphology and hence the properties can be regulated easily and efficiently. Blends containing thermoplastic starch (non crystalline starch) may be blended or grafted with biodegradable polyesters, such as polycaprolactone, to increase flexibility and resistance to moisture. Blends mainly formed into films and sheets, that are used for foaming and injection molding. By mixing thermoplastic starch with cellulose derivatives, rigid and dimensionally stable injection molded articles result. Seeding and weeding in paddy is an essential component in paddy production. There are many models of seeders and single row cono weeders available in the market which are being used for mechanized seeding and weeding operation. These are basically made with Mild Steel which has certain disadvantages in terms of machinability, reproducibility, weight, life, appearance etc. An improved manually operated 8-row drum seeder (plastic moulded) for direct sowing of pre-germinated paddy for wetlands and plastic moulded cono weeder developed was evaluated for its performance in various farmers field. It was observed that the cost of production of plastic moulded eight row drum seeder and plastic moulded cones for cono weeder was almost on par to that of these equipment made with MS sheet. Field studies revealed that plastic moulded seeder and cono weeder recorded higher field capacity, seeding/ weeding index and performance index over implement made of MS, with lower working force and plant damage. The ergonomic study revealed that heart beat/min, VO2/min, ODR score, body part discomfort score, OCR as VO2 max, per cent of plastic moulded equipment was found better over metallic model of equipment. This clearly gave an indication that there is a scope for substitution of MS material by polymers in rice mechanization. This paper deals with production process and performances evaluation of plastic moulded cono weeder for wet land paddy production.

The Use of an In-Situ Measurement to Probe the Solidification Kinetics of Injection-Molded HDPE/PP Blends

The largest portion of an injection molding (IM) cycle is actually occupied by the melt cooling stage, which also significantly dictates many end-use properties of the final parts, especially for crystalline polymers which undergo both solidification and crystallization processes simultaneously. The solidification kinetics of HDPE/PP blends were investigated under injection molding conditions with the aid of an in-situ measurement of in-cavity temperature profiles throughout the IM process. The obtained experimental results were in good agreement with our previous theoretical predictions. The present study will be instructive to the optimization of processing variables, and supplies good insight into the formation of various crystalline structures in injection-molded articles.

Probing solidification kinetics of high-density polyethylene during injection molding using an in-situ measurement technique

The largest part of an injection molding cycle is occupied by melt cooling, which significantly influences the properties of the final parts, especially for crystalline polymers which undergo both solidification and crystallization processes simultaneously. Based on non-isothermal crystallization characterization, solidification kinetics of high density polyethylene was investigated via an in-situ measurement of in-cavity temperature profiles throughout the injection molding process. Existence of the turning point in the cooling curve of ln θ vs. ln t, which can be employed for estimation of the minimum cooling time, was for the first time validated experimentally. Good agreement was achieved through the comparison between experimental observations and theoretical predictions using the enthalpy transformation method (ETM). The present study will be instructive for the optimization of processing variables, and gives insight into the formation of various crystalline structures in injection molded articles, as well as forecast of cooling time of injection moldings of crystalline polymers.

Plant polymer biodegradation in relation to global carbon management

Natural polymers such as starch, protein, and algae are renewable and sustainable materials. They are used in many industrial applications such as polymeric blends for films, fibers, and injection molded articles. However, biodegradability of these materials in anaerobic sludge digestion is largely unreported. Extensive laboratory results were acquired to elucidate biodegradability and biodegradation kinetics of the selected materials according to ASTM D5210. There was no remarkable difference in biodegradability of wheat, native corn, and modified corn starches. For the protein samples, wheat gluten biodegraded to a great extent than soy protein isolate. For the algal samples, Spirulina biodegraded to a great extent than Nannochloropsis. A first order kinetic equation was used to fit all experimental data. A separate set of 14C data examined if the carbon source, which is a building-block for all plant polymers, was bio-based (recent carbon) or fossil-based. The former is a part of global carbon cycle, and the latter is believed to cause adverse greenhouse gas effects resulting in global warming.

The Surface Quality of Low-Pressure Injection Molded Articles Obtained by a Cavity/Core Mold Pair Given a Difference in Temperature and/or Surface Roughness

In injection molding, it is important to manage the surface related problems of molded articles. A trial has been reported on managing sinkmarks concentrated to the one-sided surface of moldings through giving a mold temperature difference. Our experiment here was conducted for clarifying how the uneven sinkmark development influenced the surface transfer, under the combined conditions of a low injection pressure with a given difference in temperature and roughness in the mold having mirror-cavity and rough-core surface. The evaluation was performed by glossmetry at the cavity side and by volumetry of sunk-space at the core side.

Numerical and experimental investigation of shrinkage behavior of precision injection molded articles. I. Development of lateral motion modeling

AbstractThe present study aims at improving the state of art physical modeling in the numerical simulation for a precision injection molding to take into account the shrinkage behavior observed by experimental measurements. In Part I, new lateral motion models have been developed to predict the birefringence, residual stress profiles, and effects of various processing conditions on the shrinkage altogether. In conventional models, the lateral motion is either allowed too early or totally prohibited in the cooling stage. With the new modeling, more general description of lateral motion has been achieved either by allowing the lateral motion if an averaged lateral residual stress reaches a certain value or by letting the lateral motion develop continuously when a shearing strength is equal to an estimated shear stress. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Numerical and experimental investigation of shrinkage behavior of precision injection molded articles. II. Results and discussion

AbstractIn the accompanying paper, Part I, presented are the physical modeling and numerical formulation of new lateral motion modelings. In Part II, new models developed in Part I are validated by the successful comparison of calculated residual stress profile with the literature data. The predicted results of the birefringence, residual stress distribution, and shrinkage from new lateral motion modeling are in better agreement with corresponding experimental data than those from the conventional ones. The new model prediction falls between those of two extreme cases corresponding to conventional models. As a result of extensive parametric study of processing conditions, the developed analysis system is found to be capable of successfully predicting the tendency of shrinkage behavior varying with most of processing conditions. In this regard, the new model enables better analysis based design and optimization of precision injection‐molded products. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Improving mechanical performance of injection molded PLA by controlling crystallinity

AbstractCurrently, use of poly(lactic acid) (PLA) for injection molded articles is limited for commercial applications because PLA has a slow crystallization rate when compared with many other thermoplastics as well as standard injection molding cycle times. The overall crystallization rate and final crystallinity of PLA were controlled by the addition of physical nucleating agents as well as optimization of injection molding processing conditions. Talc and ethylene bis‐stearamide (EBS) nucleating agents both showed dramatic increases in crystallization rate and final crystalline content as indicated by isothermal and nonisothermal crystallization measurements. Isothermal crystallization half‐times were found to decrease nearly 65‐fold by the addition of only 2% talc. Process changes also had a significant effect on the final crystallinity of molded neat PLA, which was shown to increase from 5 to 42%. The combination of nucleating agents and process optimization not only resulted in an increase in final injection molded crystallinity level, but also allowed for a decreased processing time. An increase of over 30°C in the heat distortion temperature and improved strength and modulus by upwards of 25% were achieved through these material and process changes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Morphology and Properties of Soy Protein and Polylactide Blends

Blends of soy protein (SP) and a semicrystalline polylactide (PLA) were prepared using a twin-screw extruder. The melt rheology, phase morphology, mechanical properties, water resistance, and thermal and dynamic mechanical properties were investigated on specimens prepared by injection molding of these blends. The melt flowability of soy-based plastics was improved through blending with PLA. Scanning electron microscopy revealed that a co-continuous phase structure existed in the blends with soy protein concentrate (SPC) to PLA ratios ranging from 30:70 to 70:30. SPC/PLA blends showed fine co-continuous phase structures, while soy protein isolate (SPI)/PLA blends presented severe phase coarsening. At the same SP to PLA ratios, SPC/PLA blends demonstrated a higher tensile strength than SPI/PLA blends. The water absorption of soy plastics was greatly reduced by blending with PLA. The compatibility was improved by adding 1-5 phr poly(2-ethyl-2-oxazoline) (PEOX) in the blends, and the resulting blends showed an obvious increase in tensile strength and a reduction in water absorption for SPI/PLA blends. The compatibility between SP and PLA was evaluated by mechanical testing, dynamic mechanical analysis (DMA), water absorption, and scanning electron microscopy (SEM) experiments. Differential scanning calorimetry (DSC) revealed that PLA in the blends was mostly amorphous in the injection molded articles, and SP accelerated the cold crystallization and could increase the final crystallinity of PLA in the blends.

Shear‐induced migration of conductive fillers in injection molding

AbstractThe effect of shear‐induced conductive filler migration on surface and volume conductivity of injection molded articles of polystyrene and polypropylene with carbon black was investigated. It was found that the loss of conductivity was most significant when the mean particle concentration was at or slightly above the percolation threshold. The compounds with mean particle concentration well above the percolation threshold showed no loss at all. The conductivity decreased with the increase of shear rate used in molding. The removal of surface layers by excimer laser led to restoration of the conductivity to the value of well‐mixed, compression‐molded specimens. The thickness of surface layer removed before conductivity was restored was found to be a strong function of the shear rate and the nature of polymer used. Polym. Eng. Sci. 44:2101–2109, 2004. © 2004 Society of Plastics Engineers.

Injection moldability and properties of compatibilized PA6/LDPE blends

AbstractAn ethylene‐acrylic acid copolymer (EAA), either alone or combined with a low molar mass bis‐oxazoline compound (PBO), has been used as a compatibilization promoter for blends of polyamide‐6 (PA6) with low‐density polyethylene (LDPE). The effect of compatibilization on blend processability in injection molding operations and on the properties of the molded specimens has been studied. In the absence of compatibilization, the injection molded articles were shown to have low‐quality surface appearance and poor mechanical properties. Both these characteristics were appreciably improved as a result of reactive compatibilization of the blends with EAA and, even more, with the EAA‐PBO couple. In fact, the finished articles prepared by injection molding of the quaternary blends were shown to possess good surface appearance, fine and stable morphology and satisfactory mechanical properties. The results confirm the conclusion of a previous study, i.e., that the PBO fourth component may promote the in situ formation of PA6‐g‐EAA copolymers, by reaction with both the functional groups of PA6 and the carboxyl groups of EAA. Polym. Eng. Sci. 44:1732–1737, 2004. © 2004 Society of Plastics Engineers.

Optimization of Cooling Systems in Injection Molds by an Easily Applicable Analytical Model

The production rate of injection-molded articles is determined by the cooling time of the polymer melt in the mold. By using state-of-the-art numerical software the mold design can be optimized in order to achieve fast cooling. However, the efforts required to apply this software do not always justify its use in dealing with the daily design problems. Taking the changing mold wall temperature into account a straightforward analytical procedure for optimizing the cooling channel lay-out for a thermoplastic resin has been developed. The equations in the model can be easily solved by means of a hand-held calculator, thus enabling quick estimates of the effect of relevant parameters on mold design. Results of numerous simulations and a worked-out example illustrate the application of the model which has led to good results in practice.

Physically based dynamic model for control of cavity pressure in injection moulding of amorphous plastics

Cavity pressure plays an important role in determining the quality of injection moulded articles. However, the non-linear and time varying behaviour of the process causes difficulties in implementing an efficient control system, since these generally employ linear time invariant design strategies. Conversely, advanced control methods such as self tuning control do not provide physical information about the process. A physically based model has been developed. This model is used to control cavity pressure during the filling and packing phases. Experimental results indicate that this control yields accurate results for the injection moulding of polystyrene. Different control algorithms with different tuning criteria were implemented on a microcomputer to control the cavity pressure. The results indicate that this method is superior to the classical empirical control approach.

Physically-Based Adaptive Control of Cavity Pressure in Injection Molding: Filling Phase

Abstract Cavity pressure plays an important role in determining the quality of injection molded articles. The non-linear and time-varying nature of the process causes difficulties in implementing efficient control systems, which usually employ linear, time-invariant design strategies. Conversely, advanced control methods, such as self-tuning control, do not provide physical information about the process. A physically-based adaptive controller has been developed for cavity pressure control during the filling phase. Different control algorithms, employing different tuning criteria, were implemented on a microcomputer to control the cavity pressure. Experimental results indicate that this control yields accurate results for the injection molding of polyethylene. The results also show that this method, using the IMC algorithm, is superior to the classical optimal controller tuning approach.

Injection Molding of LDPE/BaSO4 Blends

Abstract The injection mold filling behavior of a blend of low density polyethylene (LDPE) and barium sulphate (BaSO4) was studied experimentally and compared with that of pure LDPE. The method of short shots was used to analyze the mold filling behavior. An experimental study using a full factorial design was implemented with the following factors: mold temperature, injection speed and injection time. Experimental results and computer simulation predictions of the mold filling stage were found to be in acceptable agreement. The produced short shots with the LDPE/BaSO4 blend have significantly lower percentages of volume filled than those of the corresponding short shots with the pure LDPE. The increase in the melt viscosity and density of the polymer resin with the addition of BaSO4 cannot be neglected when producing injection molded articles with LDPE/BaSO4 blends. To study the deviations between the experimental results and the computer simulation predictions, a factorial numerical study was completed. The results show that the simulation predictions are significantly affected by the accuracy of the polymer material properties.

Nucleating agent effects on selected properties of polypropylene

AbstractA study of nucleating agent effects on the selected optical and mechanical properties of a semicrystalline homoisotactic polypropylene is presented. The results showed that the type and concentration of the nucleating agents to be added, and the screw speed during the compounding process, were of vital importance. It was also noticed that the improvement in optical clarity due to the addition of the additive might not necessarily benefit the mechanical properties of injection molded articles.