Thickening and Rheological Properties of Crystalline Polyester Used in Low Pressure Sheet Molding Compounds

Low pressure sheet molding compound （LPMC,1.0-3.0 MPa,95-103 ℃） is a new kind of thermosetting material with crystalline polyester as a physical thickenner.LPMC is different from conventional SMC using an earth oxide thickening agent （e.g.MgO） as chemical thickenner,it relies on the physical thickening of crystalline polyester.Crystalline polyester resin is the key material to mold LPMC parts.Currently there was no report about the thickening mechanism of crystalline polyester in LPMC.In this article,crystalline polyester resins,whose melting points were between 45 ℃ and 89 ℃,were synthesized by a two-step esterification.The melt points of crystalline polyesters are controlled by regulating the mol ratio of the two glycols and the two acids.And by means of varying the content of crystalline polyester resin,the thickening effect on resin paste is investigated.In addition,the thickening mechanism of crystalline polyester in LPMC was investigated by FTIR and DSC analysis.The effects of the diameters and viscosity of crystalline polyester on the rheological property and fiber distribution of LPMC sheets were studied,too.Results show that the thickening effect is excellent when the weight content of crystalline polyester resin is 3%.And there exists three kinds of functions acting in the process of thickening：swelling,hydrogen bonds and induction crystallization.During the preparing process of resin paste in LPMC,the temperature of resin paste must be kept at 90 ℃.In addition,crystalline polyester make LPMC have a perfect fluid property.When the viscosity of LPMC sheet is beyond 1 kPa s,the fiber orientation is not obvious.But when the viscosity of LPMC sheet is about 500 Pa s,the fiber shows a certain degree of orientation.Moreover the study of physical and chemical thickening mechanism of crystalline polyester and the rheological discipline of LPMC sheets in the hot mould will provide the researchers and enterprises with theory guidance.

Numerical Simulation of Phenolic Sheet Molding Compound in Compression Molding

Based on generalized Hele-Shaw (GHS) model, a numerical simulation of phenolic sheet molding compound (P-SMC) in compression molding is realized by finite element step-by-step computing method. Finite elemental computing and post analysis programs have been written. The compression mold filling process, time and pressure requirements of P-SMC in a closed mold are predicted, and a good agreement is shown when compared with experiments. It will be of theoretical significance for the mold design and the optimization of the technological parameters in the compression molding of sheet molding compound.

Effect of Atmospheric Pressure Plasma Treatment on the Lap-Shear Strength of Adhesive-Bonded Sheet Molding Compound Joints

Atmospheric pressure plasma treatment(APPT)technology was used herein to treat sheet molding compound(SMC)substrates to increase the lap-shear strength of adhesive-bondedSMCjoints.Further,the mechanisms behind the lap-shear strength improvements in APPT-treated adhesive-bonded SMC joints were explored.A maximum lap-shear strength about three times that of the as-received SMC joints was achieved when the APPT distance was set to 20 mm.The surface roughness,which exhibited little benefit to the lap-shear strength,was determined to not be the primary reason for the increase in lap-shear strength.Specifically,X-ray photoelectron spectra revealed that an increased amount of O-containing groups(i.e.,C–O–H,C–O–C,H–O–C=O or R–O–C=O)following APPT contributed to the improved lap-shear strength.In addition,the surface free energy increased significantly after APPT,which improved the lap-shear strength of the adhesive-bonded SMC joints.Compared to the change of surface morphology,the changes in both the surface chemical property and surface free energy played larger roles in increasing the lap-shear strength of APPT-treated SMC joints.