Specific Weight

A material data sheet (technical data sheet, TDS) is the document a resin supplier publishes for a specific grade, listing its tested properties and the conditions used to measure them. It is the starting reference for choosing a material and for setting up a molding process — not a guarantee for every part. ## What it contains - Rheological / processing: melt flow rate (MFR/MFI), recommended melt and barrel temperature, mold temperature, drying time/temperature and target moisture content, injection speed/pressure guidance. - Mechanical: tensile strength and modulus, elongation, flexural and impact (Izod/Charpy) values. - Thermal: heat deflection temperature (HDT), melting or softening point, continuous use temperature. - Physical: density / specific weight, mold contraction (shrinkage) — often different along and across flow, water absorption, flammability (UL94). ## How to read it Each value comes with a test standard (ISO or ASTM) and conditions; numbers are only comparable when the standards match. Most data is measured on dried virgin resin on standardized specimens, so real parts with regrind, fillers, weld lines or thin walls can differ. Use the sheet for drying and start-up settings, then confirm with your own process and parts. ## Related terms - See also: resin, moisture content, specific weight, contraction, regrind ## What is a material data sheet? A supplier document for a specific resin grade listing its tested mechanical, thermal, physical and processing properties, together with the test standards and conditions used to measure them. ## What information is on a material data sheet? Melt flow rate, recommended melt/mold temperatures, drying conditions and moisture target, density/shrinkage, plus tensile, flexural, impact and heat-deflection values — each tied to an ISO or ASTM test method. ## Why are data sheet values different from my real parts? Because the sheet is measured on dried virgin resin using standardized specimens; regrind, fillers, moisture, weld lines, wall thickness and your actual process all shift the real-world results.

A plastic is a synthetic or semi-synthetic material whose backbone is a polymer — long chains of repeating molecular units — usually combined with additives that tune color, stability, flow and strength. The word "plastic" refers to its plasticity: when heated it can be shaped and then set into a solid part, which is exactly what injection molding exploits. ## Plastic vs polymer vs resin - polymer: the pure long-chain molecule (e.g. polyethylene). - Plastic: the usable material = polymer + additives, the everyday term for the finished compound. - resin: in a molding shop, the pelletized plastic fed into the machine. In practice molders use "resin," "plastic" and "material" almost interchangeably. ## The two families that matter for molding - thermoplastic: softens when heated and re-solidifies when cooled, reversibly — so it can be melted, molded, reground and re-melted. Virtually all injection molding uses thermoplastics. - thermoset: cures into a permanent crosslinked network and cannot be re-melted (e.g. epoxy, phenolic). Molded by different processes. ## Structure that drives behavior Thermoplastics are either amorphous (random chains — PC, ABS, PS: gradual softening, lower shrink, often clear) or semi-crystalline (ordered regions — PP, PA, POM: sharp melting, higher shrink, chemical resistance). This structure sets melt behavior, viscosity, shrinkage and where the molding process window lives. ## Related terms - See also: polymer, thermoplastic, thermoset, resin, additive ## What is plastic made of? A base polymer — long repeating molecular chains, usually from petrochemicals or increasingly bio/recycled sources — blended with additives such as stabilizers, colorants, lubricants and reinforcements to reach usable properties. ## What is the difference between a plastic and a polymer? A polymer is the pure long-chain molecule; a plastic is the usable material made from that polymer plus additives. In molding, the pelletized plastic fed to the machine is usually called resin. ## What kinds of plastic are used in injection molding? Almost always thermoplastics, which melt and re-solidify reversibly — split into amorphous grades (PC, ABS, PS) and semi-crystalline grades (PP, PA, POM); thermosets cure permanently and use other processes.

Resin is the polymer raw material that injection molding turns into parts — the base plastic, usually compounded with additives and supplied as pellets. In the molding world "resin", "polymer" and "material" are used almost interchangeably for what goes into the hopper. ## Families of molding resin - Commodity: high volume, low cost — PP, PE, PS, PVC. - Engineering: better mechanical/thermal performance — ABS, PA (nylon), PC, POM, PBT. - High-performance: extreme heat/chemical resistance — PEEK, PEI/ULTEM, PPS, LCP. A resin can be thermoplastic (re-meltable, the norm for injection molding) or thermoset (cures permanently). Grades are often filled (glass fibre, mineral) to boost stiffness and reduce shrinkage. ## How resin behaves in molding Each grade has a material data sheet giving melt temperature, mold temperature, drying conditions and shrinkage. Key practical points: - Drying: hygroscopic resins (PA, PC, PET) must be dried or moisture causes splay and weak parts. - melt window: too cold and it won't fill; too hot and it degrades. - Regrind: clean scrap can return as regrind mixed with virgin resin, within limits. ## Related terms - See also: pellet, thermoplastic, virgin resin, regrind, material data sheet ## What is resin in injection molding? It is the plastic raw material — a polymer plus additives, supplied as pellets — that is melted and injected to form parts. ## What is the difference between resin and plastic? In practice they are used interchangeably; "resin" emphasises the raw polymer feedstock, while "plastic" often refers to the finished material or part. ## What types of resin are used in injection molding? Commodity (PP, PE, PS), engineering (ABS, PA, PC, POM) and high-performance (PEEK, PPS) thermoplastics, often available glass-filled.

Viscosity is a fluid's resistance to flow. For a polymer melt it governs how easily the resin fills the mold: high viscosity means stiff flow that needs more pressure, low viscosity flows easily but can flash. ## Polymer melts are shear-thinning Unlike water, a thermoplastic melt is pseudoplastic (shear-thinning): its viscosity drops as the shear rate rises. Faster injection speed shears the melt more and thins it, which is why fast fill can need less pressure than slow fill. Viscosity also drops as temperature rises (barrel temperature). ## What changes viscosity - Temperature: higher melt temperature → lower viscosity. - Shear rate: higher injection speed → lower viscosity. - Molecular weight / grade: higher MW (lower melt-flow index) → higher viscosity. - Moisture and degradation: can lower or raise it unpredictably. ## Why it matters Viscosity sets the fill pressure, the process window and gate/runner sizing. In scientific molding a viscosity curve (relative viscosity vs fill speed) finds the speed where the melt is least sensitive to small changes, for a more robust process. (Note: lab relative viscosity is a different, dimensionless ratio used to grade resins like PA.) ## Related terms - See also: melt, injection speed, barrel temperature, injection pressure, relative viscosity ## What is viscosity in injection molding? It is the melt's resistance to flow; it drops with higher temperature and higher shear (injection speed) and sets how much pressure is needed to fill the mold. ## Why does melt viscosity drop at high injection speed? Polymer melts are shear-thinning: more shear untangles and aligns the molecules, lowering viscosity — so a faster fill can need less pressure. ## What affects melt viscosity? Melt temperature, shear rate (injection speed), the resin's molecular weight / melt-flow index, and moisture or thermal degradation.