Published · 5 min read
Machine direction (MD) and transverse direction (TD) need not produce the same PE-film values. For Poşetsan Date, a useful specification defines load direction, elongation and service conditions as well as micron. Poşetsan and Date Plastik therefore read film data alongside the actual bag application.
Why MD and TD can behave differently
Extrusion, drawing and winding can influence polymer structure in the processing direction. Strips cut from one roll may consequently show different tensile force, elongation or stiffness by orientation. ASTM D882 is a method for tensile properties of thin plastic film and sheeting; direction and test conditions are part of the result.
A high result in one direction does not prove suitability in the other. A sack carried along its long side and a bag stressed transversely by a product corner do not see the same load. Acceptance criteria should follow the real load path.
Build the test plan correctly
Preserve specimen orientation
Mark MD and TD on every strip cut from the roll. Record lot, thickness, cut position, conditioning and test speed before comparing results. Taking enough specimens from separate roll positions makes variation visible instead of hiding it in one number.
Do not read breaking force alone
The tensile curve provides elongation and, where needed, modulus alongside breaking force. A very stiff film may not accommodate sudden product movement, while an overly extensible structure may affect bag shape or machine settings. The decision is a balance, not the largest single value.
Transfer the data to bag design
Map the load source onto the bag: carrying point, long edge, seal line and sharp product corner each change the direction. Repeating failure across TD cannot be cleared by MD data alone. A failure close to a seal should also be assessed separately from tensile behaviour in the film body.
Label the roll MD arrow and cutting position.
Prepare separate specimen sets for MD and TD.
Record thickness near each specimen.
Note whether failure occurs in the grip or gauge length.
Confirm laboratory findings with filled-pack and transport trials.
Make results comparable
Different methods, specimen geometry or conditions do not create a sound purchasing comparison. A report should keep direction, average, variation and observed failure mode together. ASTM D882 is a tool for seeing directional behaviour; it does not represent every packaging performance by itself.
Product mass, sharpness, filling speed, seal design and storage temperature also affect the application. Specimen tests and trials with the packed product therefore complement one another.
PE bags and sacks · PE bag production capabilities · micron selection guide
Uygulama notu / Application note
Extrusion, drawing and winding can influence polymer structure in the processing direction. Strips cut from one roll may consequently show different tensile force, elongation or stiffness by orientation. ASTM D882 is a method for tensile properties of thin plastic film and sheeting; direction and test conditions are part of the result. Mark MD and TD on every strip cut from the roll. Record lot, thickness, cut position, conditioning and test speed before comparing results. Taking enough specimens from separate roll positions makes variation visible instead of hiding it in one number.
The tensile curve provides elongation and, where needed, modulus alongside breaking force. A very stiff film may not accommodate sudden product movement, while an overly extensible structure may affect bag shape or machine settings. The decision is a balance, not the largest single value. Map the load source onto the bag: carrying point, long edge, seal line and sharp product corner each change the direction. Repeating failure across TD cannot be cleared by MD data alone. A failure close to a seal should also be assessed separately from tensile behaviour in the film body.
Different methods, specimen geometry or conditions do not create a sound purchasing comparison. A report should keep direction, average, variation and observed failure mode together. ASTM D882 is a tool for seeing directional behaviour; it does not represent every packaging performance by itself.
When discussing an application with Poşetsan Date, share the load direction, product geometry and failed samples. That gives Poşetsan and Date Plastik a repeatable starting point for the test plan.
Kontrol ve karar / Control and decision
When setting an acceptance limit, first state which property is critical in the process. A bag exposed to a brief high load in handling may need elongation reserve, while a sustained hanging load may make stiffness more relevant. The same nominal thickness does not guarantee the same directional behaviour across formulations or process settings. A purchase specification should therefore state measured directions, conditions and the intended application, not thickness alone.
When setting an acceptance limit, first state which property is critical in the process. A bag exposed to a brief high load in handling may need elongation reserve, while a sustained hanging load may make stiffness more relevant. The same nominal thickness does not guarantee the same directional behaviour across formulations or process settings. A purchase specification should therefore state measured directions, conditions and the intended application, not thickness alone.