The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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The Assessment of Uncertainty in Spectrophotometry
Ideally, manufacturer specifications provide performance characteristics and specifications that can be used to evaluate the suitability of colorimeter and spectrometer measuring and test equipment for a given application. However, understanding specifications and using them to compare equipment from different manufacturers, the quality of products, and its adherence to specifications can be a perplexing task. This primarily results from inconsistent terminology, units, and methods used to develop and report equipment performance specifications. This paper discusses how to determine if manufacturer specifications are adequate for the intended purpose, and how to interpret and assess colorimeter and spectrometer performance and reliability. Recommended practices are presented and an illustrative example is given for combining components values into a specification.
Gas Chromatography Applications in Food Flexible Packaging Covering Food Safety, Process Control, Polymer Additive Analysis and Analysis of New Generation Packaging with a Compendium of Illustrations
Gas Chromatography (GC) is used extensively in Food Flexible Packaging for quick and accurate analysis of solvents retained from solvent based liquid printing inks, adhesives and coatings. This paper covers recent a recent development in Head Space technology, the Dynamic Head Space with Purge & Trap, which ensures complete extraction of high boiling points solvents such as ethyl cellosolve, propyl cellosolve, toluene and methyl iso butyl ketone in addition to low boiling point solvents such as ethyl alcohol, ethyl acetate and methyl ethyl ketone. Identifying all solvents in full measure is critical for food safety. The paper mentions the fast GC concept, with suitable spilt injection ratio, a special shorter length capillary column and Flame Ionization Detector (FID) with high sampling frequency and data acquisition capability which can help in quick analysis for control of speed, drying hood air flow and dryer temperature station wise in printing, lamination and coating. Analysis of the levels of slip and anti-block additives after production of the sealant layer film, after lamination, after curing and post storage needs to be measured for validation and standardization of processes and sourcing of raw materials.GC analysis is relatively fast and simple. Nano-technology is being increasingly used in food packaging for performance improvement. SiOx coating on Bi-axially Oriented Polyester (BOPET) Films improves barrier to levels matching aluminium foil and thereby facilitates see-through packaging. The paper describes a method for analysis of performance of such coatings. The aim of the paper is to help the food flexible packaging industry to fully exploit the capabilities of advanced Gas Chromatography to ensure food safety, optimize processes and enhance shelf performance.
Synthesis and Characterization of Antimicrobial Polyvinyl Pyrrolidone Hydrogel as Wound Dressing Hints
A novel antimicrobial hydrogel (PVP-GP) was prepared by covalently bonding polyvinyl pyrrolidone (PVP) with poly(hexamethylenediamine guanidine hydrochloride). The products were characterized by 1H NMR, FTIR, SEM, and their performances for wound dressing applications were also evaluated. Swelling study showed that the water absorptivity of PVP-GP hydrogels decreased as the crosslinking density increased either in water or in physiological saline solution. The water vapor transmission rates (WVTR) of PVP and PVP-GP hydrogels were in the range of 1727 ~ 2320 g/m2/day, indicating that the prepared hydrogels were suitable for wound dressings without dehydrating the wound surface or accumulating exudates. Kirby-Bauer inhibition zone tests and microbe penetration assay proved that the PVP-GP hydrogels had high antimicrobial activity.
Superior Processability and Economics of Single Site LLDPE vs. Conventional Metallocene LLDPE Blown Films
Over the past 15 years, the polyethylene industry has increasingly focused on metallocene and single-site catalyzed LLDPE as the route to higher performance. Unfortunately, the improvement in physical properties over conventional Ziegler-Natta (Z/N) LLPDE is counterbalanced by a dramatic decrease in output rates which directly impacts the economics of these film structures. To compensate, blown film producers add 10%-20% of LDPE into these resins to the detriment of the film physical properties. A unique class of single-site catalyzed LLDPEs (sLLDPE) has been developed which overcomes the processability issues encountered with the traditional metallocene LLDPE (mLLDPE) resins thus reducing the demand for LDPE and maintaining the enhanced physical property performance. This paper focuses on: The comparison of bubble stability and maximum output of sLLDPE vs. mLLDPE resins. The economic cost associated with mLLDPE vs. sLLDPE in a commercial film structure via a case study.
An Investigation of the Effects of Bound Selection on the Numerical Formulation of Kinetic Parameters
Kinetic modeling is used to predict the rate of conversion of a partially cured thermosetting plastic subjected to catalytic conditions of temperature and pressure. Parameters for these models can be determined from experimental data obtained through differential scanning calorimetry (DSC). In the present study, kinetic parameters are determined from dynamic DSC scans of the Pro-Set 117LV/229 resin system. The primary contribution of this paper is an evaluation of the sensitivity of empirical kinetic parameters to the selection of reaction bounds. This study is performed using a finite difference approach to obtain parameter sensitivity. The results suggest that the kinetic parameters are insensitive to bound selection for this particular resin system. Additionally, the kinetic parameters obtained from dynamic scans are applied to isothermal DSC results, which indicates the importance of the accurate determination of kinetic parameters at low degrees of conversion and the evaluation of diffusion control. The effects of gelation and vitrification are also considered.
Manufacturing Induced Curvature of Carbon Fiber Laminates: Experimental Observation and Model Validation
The use of carbon fiber reinforced composites is becoming increasingly implemented throughout the entire aerospace, automotive and many niche industries, in large part due to their high strength to weight ratios. Unfortunately, effective design of the fabrication process and the final part performance poses increased engineering difficulties over alternative manufacturing approaches. This work focuses on the residual strains that occur within the processed laminate as induced during manufacture. These residual strains are due to a combination of the curing kinetics of the thermoset and the induced thermal strains caused by a coefficient of thermal expansion mismatch for the resin and carbon fiber. In the present paper, we present results for a cross-ply (un-balanced) laminate. We use micromechanical theories to predict the stiffness and the coefficient of thermal expansion of an individual lamina from the constitutive properties for the fiber and the matrix, and couple the lamina results with a finite element structural and coupled thermal-structural analysis to predict the observed macroscopic deformation and curvature of an unloaded processed laminate. The finite element results are compared with the measured results and show exceptional qualitative agreement with experimental observations. Suggestions for improvements on the method are introduced along with a discussion of the need for the quantification of the relevant constitutive material properties for future modeling and experimental studies.
Prediction of Fiber Orientation Tensor in Glass Fiber Reinforced Polymer
Application of chopped glass fiber reinforced polymer components from injection and compression molding process are rapidly increasing in automotive industry due to the light-weight and their mechanical properties. Material properties of such components strongly depend on fiber orientation. Therefore it is very important to estimate the fiber orientation distribution in such materials. In this paper we are presenting a practical method to estimate the fiber orientation from CT scan image. A 3D image of fibers is created and 2nd order orientation tensors are calculated using the coordinates of the end of fibers. The approach is demonstrated on a 3-D box shaped structure. The measured orientation tensors are compared with the predicted values from the mold-fill simulation. Key challenges in measuring the orientation tensor for the long fibers is also discussed.
Insert Injection Molding Simulations for Lens Encapsulation of Liquid Crystal Displays
An insert injection-compression molding process was used to encapsulate cholesteric liquid crystal displays with flexible and rigid lens. For this purpose, a complex hot runner mold was designed and constructed. Thermoplastic polyurethanes (TPU) were found to be the best candidates for this application after a vigorous search on desired physical properties for lenses including transparency, low melt viscosity and melting temperature and mechanical properties. Three different hardness grades of TPUs were selected to demonstrate the range of encapsulation from soft to hard. In this process, the encapsulation was accomplished in two steps: first, injecting the TPU on the front of the display from an edge pin gate and subsequently the back side of the display is encapsulated. A flow simulation is completed on Autodesk Moldflow Insight to help pre-visualize the changing process parameters effect on part quality and to compare with experimental results. The quality of encapsulation and shrinkage related problems and their elimination are discussed in this study.
Using the Flexural Modulus to Evaluate the Accuracy of Existing Fiber Interaction Models for Predicting the Fiber Orientation in Injection Molded Thermoplastics
Advances in modeling the mold filling process have led to better designs and manufacturing efficiencies of short?fiber fiber reinforced thermoset plastics. The flow characteristics during processing dictate the spatial varying fiber orientation, and thus the spatially varying mechanical properties. Knowledge of the fiber orientation allows for part optimization of both the mold design and the processing parameters. The classical fiber?fiber interaction model Folgar?Tucker (1984) for calculating the fiber orientation for fiber filled thermoplastics has seen extensive use within the industry for nearly 30 years. Recent modifications of the classical model include the reduced strain closure (Wang et al., 2008) and the anisotropic rotary diffusion model (Phelps and Tucker, 2009). Each of these models yield quite different characteristics in the resulting predicted fiber orientation. In this paper we suggest that the predicted flexural modulus from these different fiber interaction models may be quite different and may be an effective macroscopic structural test to identify acceptable diffusion models and possibly to quantify the appropriate empirical parameter ranges for acceptable interaction models. In this work, the velocity gradients are computed along streamlines of a complex domain of an injection?molded ASTM flex bar. The fiber orientation is then obtained along each streamline from the velocity gradients and then from an in?house code the local stiffness tensor is obtained as a function of position within the entire part. Lastly, the nodal stiffness values are imported back into the finite element software to perform structural bending tests as a function of length along the part. The results show a structural response that is significantly different between the different fiber interaction models, and thus lends credence to the possibility that flex tests may be a useful experimental technique to compare fiber interaction models.
Poly(butylene succinate)/fumed silica nanocomposite: functionality and rheology
Plastics Engineering Department, University of Massachusetts Lowell Nanocomposites based on biodegradable poly(butylene succinate) (PBS) and silica fillers were prepared by a melt-blending process. Two types of unmodified fumed silica and octadecyltrichlorosilane (OTS) functionalized silica were used as fillers. Rheology was used to study relaxation dynamics and viscoelastic properties of these nanocomposites in the melt state. The effects of polymer-particle and particle-particle interactions on viscoelastic properties of nanocomposite materials were investigated. Linear viscoelastic data indicate a transition to a solid-like response at low oscillation frequencies for particle weight fractions as low as 5%. The long-time response upon a step shear strain demonstrates that liquid-like behavior persists in the nanocomposites below 5 wt% loading, which is related to the relaxation of the temporal polymer-particle network. Dynamic viscoelastic and dynamic mechanical thermal analysis (DMTA) measurements of the PBS/silica nanocomposite reveal that fumed silica with the smallest primary particle size has the largest dynamic moduli over the testing temperature range. The hydrophobic functionalization of silica filler does not appreciably change the thermal transition temperatures in the nanocomposites.
Flowability Software for Powder Produced By Raleigh Disturbances for SLS
Powders for additive manufacturing processes such as Selective Laser Sintering (SLS) are currently produced by costly cryogenic milling or precipitation processes for a limited selection of resins. A nowel technique allows production of pellets in the micrometer-scale by extruding a polymer melt through a capillary and perturbing it with a hot air stream which can be used for the SLS processes. Due to the fact that this micropelletization process is used to produce powder particles from different materials, the developed software is very helpful to predict the flowability of these different particle shapes and different materials and its usage for the SLS process. This software will determine the flowability characteristics of different grain shapes and will be evaluated by comparison of results provided by both, software and experimentation. In a second step, different micropelletized materials surface smoothnesses will be compared and evaluated towards their competitiveness. This validation will show a comparison of quality and performance between the different powder production processes. The goal of this work is, to produce more cost effective but competitive powders out of different micropelletized materials.
Process Parameters Effects on Microstructure and Properties of Porous PP/TiO2 Nanocomposite Films
Nanocomposites porous film based on polypropylene (PP) and titanium dioxide (TiO2) nanoparticles were prepared by the uniaxial stretching method. Effects of drawing temperature, extension rate, stretching ratio and composition of the base films on final properties and microstructure of the stretched films were studied. Water vapor permeability results showed significant decrease in permeability of the films stretched at temperatures higher than 60°C. Water vapor permeation in the porous nanocomposite films had a direct relation with nanoparticle content, extension rate and stretching ratio. Study on morphology of stretched films, using SEM, revealed that the pores form due to PP/TiO2 interfacial debonding at lower stretching ratio while higher stretching ratios cause an enlargement of the pores and formation of PP fibril structure parallel to the stretching axis. Apparent porosity values, BET surface area measurement and quantification of dye absorption on pores showed smaller dependency on process parameters.
Multi-objective Optimization of Heating System for Rapid Thermocycling Blow Mold Using Genetic Algorithm and Artificial Neural Network
A rapid thermocycling blow mold with electric heating was used to produce automobile spoiler in the present work. In order to achieve high heating efficiency as well as uniform temperature distribution on mold cavity surface, a multi-objective optimization model was proposed and a hybrid method consisting of design of experiment (DOE), artificial neural network (ANN) and multi-objective genetic algorithm (GA) was developed to optimize the heating system of the mold. The results showed that the method can effectively give the optimal values of design variables. Further, the temperature distribution uniformity on the mold cavity surface was largely improved and the heating efficiency was also guaranteed by using optimal design results.
Determining Which In-Mold Sensors Should Be Used for V/P Transfer During Injection Molding for Three Different Injection Strategies
The use of in-mold pressure and surface temperature sensors was investigated to determine whether they reduced variation in part weight when variation in material viscosity and check ring leakage were introduced to the process. Velocity to pressure transfer when the part was not quite full (2-stage, pack with second stage), after the part was packed with a fast velocity (2-stage, pack with first stage), and after the part was packed with a slow velocity (3-stage) were the injection strategies evaluated. It was found that surface temperature sensors toward the end of fill were the most beneficial in all cases studied.
Crosslinkable Polyolefin for Rotational Molding with Improved Processibility
Crosslinked plastic parts demonstrate prominent performance advantages over the non-crosslinked articles for a wide array of applications. New crosslinkable polyethylene compositions were recently developed which showed outstanding processibility and excellent thermal and mechanical properties, such as increased impact strength, high modulus, and enhanced environmental stress cracking resistance (ESCR). The advancement in balance of melt processibility and solid properties is ideally suited for the rotational molding process, opening opportunities to produce high-performance end-use products, including sporting boat, large agricultural and chemical containers, all-plastic cars, and other outdoor products.
Impact Of Crystallization On Performance Properties And Biodegradability Of Poly(Lactic Acid)
Polylactic Acid (PLA) is the most widely available, renewable and compostable polymer with several unique features. However, PLA is poor in its ability to withstand elevated use temperatures above 55 °C. As such it is common practice to either compound PLA with additives that improve its heat deflection temperature or increase its crystallinity in mold or in an extra annealing step for use in injection molded applications. The objective of this research was to study the crystallization of three PLA grades and its effect on thermal properties including compostability. Crystallization was studied using DSC and Talc was used as a nucleating agent. Crystallinity was found to vary from 25% to 60% for the various grades. The PLA was converted into test bars and cutlery and its heat distortion temperature was tested before and after annealing. Additionally, the crystallized cutlery was sent to a local composting facility and was found to disintegrate within 4 weeks, which is much sooner than the requirements of the ASTM D6400 standard of 12 weeks.
Quantifying the Friction Behavior of Amorphous and Bi-axially Stretched Polyethylene Terephthalate
Friction behavior of polyethylene terephthalate (PET) in either its amorphous or semi-crystalline form can depend on several factors. Surface microstructure and the resulting forces (Van der Waals), residual stress, the molecular weight distribution (MWD), and contaminants can influence polymer friction. A semi-crystalline polymer, PET exhibits an interesting microstructure sensitive to processing. PET is used for a range of applications with different forms. In some cases it is essential to determine the friction coefficients on molded parts. The current work presents a unique fixture built for measuring the friction of amorphous PET in the form of bottle preforms and stretched PET in the form of empty bottles, collected from high speed injection stretch blow molding (ISBM) equipment. The test frame was developed to accommodate samples with a range of contact areas, contact force, and time. The friction behavior of polymers is known to be dependent on the time and speed of the test. In the current work, dynamic friction between the molded parts were measured at a fixed rotation speed (13 RPM) and averaged over multiple samples. Data has been collected across several variables including change in chemistry, MWD, and processing changes related to cooling time. Friction on amorphous parts was higher than semi-crystalline ones. Time dependent friction behavior was observed irrespective of the microstructure. This suggests the presence of transitory micro surface features, at least on pristine surfaces.
Microcellular Injection Molding with Gas-Laden Pellets Using Nitrogen (N2) and Carbon Dioxide (CO2) as Co-Blowing Agents
A novel combination approach to producing quality foamed injection molded parts has been investigated. By combining extruded, gas-laden pellets with microcellular injection molding, the processing benefits and material characteristics of using both nitrogen (N2) and carbon dioxide (CO2) as co-blowing agents can be realized, thus yielding features superior to that of using either N2 or CO2 alone. Using an optimal content ratio for the blowing agents, as well as the proper sequence of introducing the gases, foamed parts with a much better morphology can be produced. In particular, extruding N2 gas-laden pellets, followed by microcellular injection molding with higher amounts of CO2, produces a cellular structure that is very fine and dense. In this paper, the theoretical background is discussed and experimental results show that this combined approach leads to significant improvements in foam cell morphology for low density polyethylene (LDPE), polypropylene (PP), and high impact polystyrene (HIPS) using two different mold geometries.
During the demolding process, high ejection forces can cause a local damage of the plastic part. The plastic part design as well as the design of the demolding system can be verified according to occurring stresses in the part by applying an integrative simulation already in early stage of the product development. This approach consists of a coupling of injection molding simulation and structural simulation. That way it is possible to take account of the process influence on the residual stresses in the plastic part, which may increase the contact pressure between part and mold core. For high ejection speed, it is possible to model a strain rate dependent mechanical material model to get a higher accuracy of the stress results. The validation of the simulation results in real injection molding trials show a good accordance concerning the measured and simulated demolding force.
D-LFT Molding Simulation – Verification of a new model for Fiber Orientation Prediction
The numerical simulation of fiber orientation during compression molding (CM) is a crucial and valuable tool for predicting the mechanical reliability of the final part. Considering LFT, advanced models are necessary to obtain accurate results for fiber orientation. The objective of our research is to verify new models which consider reduced strain closure (RSC) and anisotropic rotary diffusion (ARD). Since the initial fiber orientation in the charge will be considered, the first step of this project is to measure it. Using micro computerized tomography (?CT) and Volume Graphics’ (VG) VGStudio MAX image processing software for CT data analysis, the initial fiber orientation of the charge will be obtained. With the help of interpolation functions such as radial basis functions (RBF) the initial fiber orientation can be evaluated at each node of the charge mesh in the CM simulation. Model parameters are fitted by matching the experimental fiber orientation results.
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