TESTING services
Laboratory Testing
Although standardized testing methods and practices commonly do an adequate job of characterizing physical material properties, often times subtle differences in observed processing and/or product performance behaviors fall just outside the probing window of routine testing protocols. In such circumstances, materials with similar ASTM or ISO property specifications can exhibit very different processing and/or performance characteristics as a result of subtle material variations. This is where PCG usually steps in to assist its clients in recognizing and distinguishing which material properties measured in the laboratory relate to the processing & performance behaviors observed in practice. If you are seeking expert help in testing and measuring subtle differences in the physical properties of your materials, let PCG be your partner in physical material characterization. Whether you need a small quantity of materials tested for qualification purposes or you're looking to outsource some of your physical testing workload, PCG is here to help. With over a decade of experience as a scientific consulting services provider to some of the largest industrial clients in the world, PCG provides expert scientific acumen and laboratory testing services for materials spanning a broad spectrum of physical states from fluids to semicrystalline solids. Below are just some of the laboratory testing services that we provide:
extensional rheology
Extensional flow, or deformation that involves the stretching of a viscoelastic material, is the dominant type of deformation in diverging, converging and squeezing flows that occur in typical polymer processing operations such as extrusion, blow molding and injection molding. Consequently, many of the flow instabilities, irregularities and distortions that limit these melt processing operations are attributable to the extensional flow behavior of the polymer being processed. Hence, extensional rheology can often be used as a tool for fingerprinting the fundamental processing behavior of polymer melts.
In addition to elucidating fundamental melt processing behavior, extensional flow measurements are particularly useful in polymer characterization because they are very sensitive to the molecular structure of the polymeric system being tested due to the fact that flows in extension generate a much higher degree of molecular orientation and stretching than flows in simple shear. As a consequence, uniaxial elongational flows are very sensitive to crystallinity and macrostructural effects such as long-chain branching (LCB), and as such can be far more descriptive with regard to polymer characterization than other types of bulk rheological measurement.
With years of experience in developing and pioneering innovations in the field of extensional rheology (PCG President and Chief Consultant Dr. Martin Sentmanat is the inventor and pioneer of SER dual windup drum extensional rheometer technology), Polymer Consulting Group is the world's preeminent laboratory testing service provider in the field of polymer melt extensional rheology characterization and analysis. Having characterized hundreds of different types of polymeric materials and compounds over the years, PCG has pretty much covered the full spectrum of material extensional behavior and its critical role in polymer processing behavior. The following are just some of the typical extensional rheology measurements that are routinely performed for customers:
- TRANSIENT EXTENSIONAL VISCOSITY (START-UP OF STEADY EXTENSION)
- CESSATION OF STEADY EXTENSION (STRESS RELAXATION AFTER STEADY EXTENSION)
- INTERRUPTED STEADY EXTENSION
- STEP EXTENSION (TENSILE RELAXATION MODULUS)
shear rheology
Shear flow, or deformation that involves a displacement gradient within the bulk of a viscous or viscoelastic material, is the dominant type of deformation in processing operations involving screw extruders and viscous flows through channels and dies. When it comes to the rheological characterization of viscous and viscoelastic materials, shear flow deformations are commonly used because they are the easiest to generate in the laboratory. Shear rheological characterizations have been very useful in gaining insight into fundamental viscous and viscoelastic material flow behavior and in establishing fundamental material structure-property relationships for modeling material flow behavior. Shear rheology experiments are typically performed on a torsional rotational rheometer that is capable of steady rotation as well as oscillatory rotation in either a rate-controlled mode of operation or in a stress-controlled mode of operation. The PCG laboratory is equipped with research grade torsional rotational rheometers configured with environmental chambers capable of temperatures in excess of 600°C.
With decades of experience in characterizing the rheological behavior of polymeric materials in shear, from gels, to pastes, to asphalts, to polymer melts, Polymer Consulting Group is uniquely qualified to provide rheological testing services regardless of material complexity. The following are just some of the typical shear rheology measurements that are routinely performed for customers:
- DYNAMIC FREQUENCY SWEEP (STORAGE [G'] AND LOSS [G''] MODULUS)
- DYNAMIC TEMPERATURE SWEEP (GLASS TRANSITION)
- SHEAR CREEP COMPLIANCE & RECOVERY
- STEP SHEAR (SHEAR RELAXATION MODULUS)
- STEADY SHEAR VISCOSITY
- TRANSIENT SHEAR VISCOSITY (SHEAR STRESS GROWTH/START-UP OF STEADY SHEAR)
TENSILE/COMPRESSION TESTING
Tensile testing is used to characterize the strength, ductility, and physical behavior of plastic, rubber and polymer composite materials in uniaxial extension. It is commonly used to assess the mechanical performance and physical behavior of a final product as a function of aging and exposure to various chemicals and/or environmental conditions. Conventional tensile testing experiments are performed on a universal testing machine where the size of the applied deformation typically does not exceed 1000% linear elongation and the rate of the applied deformation typically does not exceed 50 mm/s (2 in/min). Most of the tensile testing measurements performed within this regime of strains and rates are often conducted according to prescribed ASTM and ISO testing standards. The following are just some of the conventional tensile testing protocols that are routinely performed for customers:
- ASTM D412: Vulcanized Rubber and Thermoplastic Elastomers
- ASTM D638: Tensile Properties of Plastics
- ASTM D882: Tensile Properties of Thin Plastic Sheeting
- ISO 37: Tensile Stress-Strain Properties of Rubber, Vulcanized and Thermoplastic Materials
PCG is also uniquely qualified to provide tensile testing services beyond the conventional ASTM and ISO standards. When working with thin films, the SER Universal Testing Platform can be used to perform miniature tensile testing on elastic solids and semi-solids over a very broad range of strain rates and at deformation speeds hundreds of times faster than can be achieved with conventional tensile testing equipment. The tensile properties of complex polymeric materials can also be characterized over a wide range of temperatures from the solid state to the softened and melt states on miniature samples weighing just a few milligrams. The SER is also capable of fluid immersion tensile testing for characterizing the tensile behavior of thin biopolymers and/or biological soft tissues within a simulated body fluid environment.
Compression testing is used to determine the physical behavior of materials under compressive or squeezing loads. The material specimen is compressed and deformation at various loads is recorded. Compression testing conducted as a function of time and temperature is often used to determine a sealant's stress relaxation behavior after being squeezed in between rigid substrates. The compression set of a material is the permanent deformation remaining when a force (that was applied to it) is removed. The term is normally applied to soft materials such as elastomers. The following are just some of the conventional compression testing protocols that are routinely performed for customers:
- ASTM D395: Standard Test Methods for Rubber Property - Compression Set
- ASTM D695: Compression Testing of Rigid Plastics and Composites
- ASTM D1621: Compressive Properties Rigid Cellular Plastics
- ISO 604: Compressive Properties of Plastics
- ISO 844: Rigid Cellular Plastics Compression Properties
Dynamic mechanical analysis (dma) TESTING
Dynamic Mechanical Analysis (DMA) testing is used to characterize the rigidity, stiffness and viscoelasticity of plastic, rubber and polymer composite materials in dynamic oscillation. It is commonly used to assess changes in the modulus of a material as a function of aging and exposure to various chemicals and/or environmental conditions. Unlike tensile testing, DMA testing involves a non-destructive evaluation of the specimen being characterized, and as a consequence it is the preferred method of mechanical evaluation when test material is limited in quantity and/or size or when the geometery of the specimen does not lend itself to tensile elongation. It is also useful in determining a material's softening point or glass transition temperature when a temperature sweep is superimposed with a fixed frequency DMA oscillation.
DMA testing experiments are typically performed on a torsional rotational rheometer often configured with an oven chamber for controlled temperature testing. Although DMA specimens are typicallay thin, flat and rectangular in geometry, the PCG laboratory is equipped with custom DMA fixturing capable of gripping specimens of circular and irregularly shaped cross-sections. The following are just some of the conventional tensile testing protocols that are routinely performed for customers:
- ASTM D4065: Dynamic Mechanical Properties of Plastics
- ASTM D5279: Dynamic Mechanical Properties of Plastics in Torsion
- ISO 6721: Dynamical Mechanical Properties of Rigid Thermoplastic Materials
PEEL/tack/adhesion TESTING
Peel/tack/adhesion testing is used to characterize the bond strength of an interface, typically defined by an adhesive layer versus a solid substrate. It is commonly used to evaluate the bonding strength of pressure sensitive adhesive (PSA) tapes, melt adhesives, uncured elastomers and other types of flexible bonding agents. Typical peel tests involve peeling two flexible substrates bonded together by an adhesive layer, or peeling a flexible substrate adhesively bonded to a rigid substrate. Peel tests are usually conducted at a constant rate and at a fixed peel angle (most commonly 180° or 90°) where the peel strength is measured in terms of a peel force per unit width of contact. Similar to peel tests, tack tests are used to determine the stickiness or tackiness of a surface. One type of quality control tack test employs a rolling ball method in which a steel ball is rolled down a well-defined incline onto a flat adhesive layer and the tack is measured in terms of the distance that the ball travels. Most commonly, however, tack is measured by either loop tack in which a PSA-coated film loop of pre-determined dimension is placed in contact with a surface or a probe method in which a small flat control surface is placed in contact with an adhesive surface and the tack is measured in terms of the peak force required to separate the surfaces. Conventional peel and tack tests are usually performed on a universal testing machine and conducted according to prescribed ASTM and ISO testing standards. The following are just some of the peel and tack testing protocols that are routinely performed for customers:
- ASTM D903: Peel Strength of Adhesive Bonds
- ASTM D1876: 180° T-Peel Resistance of Adhesives
- ASTM D2979: Pressure-Sensitive Tack of Adhesives Using an Inverted Probe Machine
- ASTM D3121: Tack of Pressure-Sensitive Adhesives by Rolling Ball
- ASTM D6195: Loop Tack
- ASTM D6252: Peel Adhesion of Pressure-Sensitive Label Stocks at a 90° Angle
- ASTM D6862: 90° Peel Resistance of Adhesives
- EN 1719: Tack Measurement for Pressure-Sensitive Adhesives - Loop Tack
- ISO 8510: Peel Test for Flexible-Bonded-to-Rigid Test Specimen
- IS0 11339: T-Peel Test for Flexible-to-Flexible Bonded Assemblies
PCG is also uniquely qualified to provide adhesive peel testing services beyond the conventional ASTM and ISO standards. The SER Technology that was developed by Dr. Sentmanat can be used to perform peel testing experiments on miniature flexible adherends and adhesive films over a very broad range of temperatures with peel rates up to 1+ m/s which is orders of magnitude faster than can be achieved with conventional peel testing apparatus. In addition, peel tests with the SER can also be performed in a peel creep mode of operation (controlled peel force as opposed to an applied peel rate) which is often more relevant to the type of adhesive failures that actually occur in real life. The SER is also capable of fluid immersion peel testing for characterizing the adhesive behavior of interfaces under fluid saturation environments.
FRICTION TESTING
Friction testing is used to characterize the ease with which two surfaces in contact are able to slide past one another. Friction results are typically reported in terms of Coefficient of Friction (COF) values, a dimensionless parameter defined by the frictional force divided by the normal force at the friction interface. There are two different values associated with the Coefficient of Friction: Static and Kinetic. Static friction applies to the force necessary to initialize motion between the two surfaces and Kinetic friction is the resistance to sliding once the surfaces are in relative motion. Friction is often measured using a sled type of method in which a flat block, or sled, of well-defined geometry is made to slide over a flat plane in which the sample to be tested is attached to either the sled or the flat plane and the associated friction force is measured. The friction force of films and thin gage webs can also be measured over cylindrical surfaces in which the web is made to slide over a portion of the round surface and the normal force is controlled by a dead weight attached to the free end of the web. Conventional friction tests are usually performed on a universal testing machine and conducted according to prescribed ASTM and ISO testing standards. The following are just some of the friction testing protocols that are routinely performed for customers:
- ASTM D1894: Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting
- ASTM G143: Measurement of Web/Roller Friction Characteristics
- ISO 8295: Plastics Film and Sheeting, Coefficient of Friction
PCG is also uniquely qualified to provide friction testing services beyond the conventional ASTM and ISO standards. PCG has developed custom friction fixtures that can be used to perform friction testing experiments on miniature friction samples over a very broad range of temperatures with sliding rates up to 1+ m/s which is orders of magnitude faster than can be achieved with conventional friction testing apparatus. In addition, friction tests can also be performed in a controlled friction force mode of operation (controlled sliding force as opposed to an applied sliding rate) which is often relevant to measuring critical slip conditions at interfaces. Fluid immersion friction measurements for characterizing the slip/traction behavior of interfaces under fluid saturation environments can also be performed.
SHRINKAGE / TENSILE CREEP & RECOVERY
Polymer shrinkage is manifested by a reduction in size of one or more part dimensions typically as a result of either thermal contraction or a material relaxation process. During polymer processing, the material shaping operations often result in residual stresses remaining in the material once it has frozen and solidified. Depending on the material temperature and molecular mobility characteristics of the polymer chains comprising the material, these residual stresses will tend to relax, and as a consequence, the initial dimensions of the frozen part will distort, contract or change over time as the polymer chains attempt to recoil. This relaxation and recoil process is usually facilitated with increasing temperature and is often more pronounced in thin-gauge components and products such as thin-walled packaging and containers. Conventional shrinkage tests are usually performed on molded or extracted specimens and conducted according to prescribed ASTM testing standards:
- ASTM D955: Measuring Shrinkage from Mold Dimensions of Thermoplastics
- ASTM D1204: Linear Dimensional Changes of Nonrigid Thermoplastic Sheeting or Film
- ASTM D2732: Unrestrained Linear Thermal Shrinkage of Plastic Film and Sheeting
- ASTM D5104: Shrinkage of Textile Fibers (Single-Fiber Test)
- ASTM D6289: Measuring Shrinkage from Mold Dimensions of Molded Thermosetting Plastics
PCG is also uniquely qualified to provide shrinkage testing services beyond conventional testing standards. Unlike conventional shrinkage testing protocols that typically only measure ultimate shrinkage, PCG has developed custom testing protocols that can be used to measure thermal expansion and shrinkage in real time as a function of programmable temperature history profiles. Material specimens can also be subjected to an applied stress duration in tensile creep mode followed by tensile relaxation/recovery/recoil in order to match the specific processing conditions of actual industrial manufacturing operations such as in shaping operations involving elastomers as well as heat shrink or shape-memory polymers.